Showing papers on "Immune tolerance published in 1995"

Fas Ligand-Induced Apoptosis as a Mechanism of Immune Privilege

Abstract: The eye is a privileged site that cannot tolerate destructive inflammatory responses. Inflammatory cells entering the anterior chamber of the eye in response to viral infection underwent apoptosis that was dependent on Fas (CD95)-Fas ligand (FasL) and produced no tissue damage. In contrast, viral infection in gld mice, which lack functional FasL, resulted in an inflammation and invasion of ocular tissue without apoptosis. Fas-positive but not Fas-negative tumor cells were killed by apoptosis when placed within isolated anterior segments of the eyes of normal but not FasL-negative mice. FasL messenger RNA and protein were detectable in the eye. Thus, Fas-FasL interactions appear to be an important mechanism for the maintenance of immune privilege.

Peripheral deletion of antigen-reactive T cells in oral tolerance.

Abstract: ORAL administration of antigen is used to induce antigen-specific peripheral immune tolerance1,2. As well as preventing systemic immune responses to ingested proteins3, oral tolerance to autoanti-gens has also been used to suppress autoimmune diseases in animals4-10and humans11,12. Both active suppression and clonal anergy are suggested to be mechanisms of oral tolerance, depending on the dose of antigen fed13,14. Here we report that oral antigen can delete antigen-reactive T cells in Peyer's patches, in mice transgenic for the ovalbumin-specific T-cell receptor genes. The deletion was mediated by apoptosis, and was dependent on dosage and frequency of feeding. At lower doses deletion was not observed; instead there was induction of antigen-specific cells that produced transforming growth factor (TGF)-β and interleukin (IL)-4 and IL-10 cytokines. At higher doses, both Thl and Th2 cells were deleted following their initial activation, whereas cells which secrete TGF-β were resistant to deletion. These findings demonstrate that orally administered antigen can induce tolerance not only by active suppression and clonal anergy but by extrathymic deletion of antigen-reactive Th1 and Th2 cells.

T Cell Awareness of Paternal Alloantigens During Pregnancy

Abstract: During pregnancy a semiallogeneic fetus survives despite the presence of maternal T cells specific for paternally inherited histocompatibility antigens. A mouse transgenic for a T cell receptor recognizing the major histocompatibility (MHC) antigen H-2Kb was used to follow the fate of T cells reactive to paternal alloantigens. In contrast to syngeneic and third-party allogeneic pregnancies, mice bearing a Kb-positive conceptus had reduced numbers of Kb-reactive T cells and accepted Kb-positive tumor grafts. T cell phenotype and responsiveness were restored after delivery. Thus, during pregnancy maternal T cells acquire a transient state of tolerance specific for paternal alloantigens.

CD28-B7 blockade after alloantigenic challenge in vivo inhibits Th1 cytokines but spares Th2.

Abstract: Blocking the CD28-B7 T cell costimulatory pathway with the fusion protein CTLA4Ig inhibits alloimmune responses in vitro and in vivo and induces tolerance to cardiac allografts in mice and rats, but the mechanisms mediating the tolerant state in vivo are unknown. Here, we report the effects and potential mechanisms of CTLA4Ig in the rat renal allograft model. LEW rats were nephrectomized and received renal allografts from major histocompatibility complex-incompatible WF rats. While all untreated and control immunoglobulin (Ig)-treated animals acutely rejected their allografts and died, 86% of rats that received a single injection of CTLA4Ig on day 2 after transplantation had prolonged survival (> 60-100 days) with preserved renal function. By contrast, only 29% of animals that received CTLA4Ig on the day of engraftment had prolonged survival. Long-term survivors (> 100 days) exhibited donor-specific tolerance, accepting donor-matched WF but acutely rejecting third-party BN cardiac allografts. Immunohistological analysis of grafts sampled at 1 week after transplantation showed that both control and CTLA4Ig-treated animals had mononuclear cell infiltrates, with a higher percentage of CD4+ cells in the CTLA4Ig-treated group. However, while this was associated with vasculitis and tubulitis in control grafts, there was no evidence of tissue injury in CTLA4Ig-treated animals. The immune response leading to graft rejection in control animals was characterized by expression of the T helper (Th) type 1 cytokines interleukin (IL)-2 and interferon-gamma. In contrast, the persistent CD4+ infiltrate without graft rejection in CTLA4Ig-treated animals was associated with increased staining for the Th2-related cytokines IL-4 and IL-10. Furthermore, grafts from CTLA4Ig-treated animals had marked upregulation of intragraft staining for IgG1, but not IgG2a or IgG2b. Administration of rIL-2 to CTLA4Ig-treated animals restored allograft rejection in 50% of animals tested. These results confirm that blockade of the CD28-B7 pathway after alloantigenic challenge induces donor-specific acceptance of vascularized organ allografts, and indicates in this model that CTLA4Ig inhibits Th1 but spares Th2 cytokines in vivo.

Unraveling Immune Privilege

Abstract: J. W. Streilein discusses the concept of immune privilege, which protects from rejection tissues grafted to certain sites in the body. The differences between immune-privileged sites and immune-privileged tissues are illustrated by two recent papers implicating the cell surface protein FasL in immune privilege in the eye ( Science , [p. 1189][1] of this issue) and in the testis [D. Bellgrau et al ., Nature 377 , 630 (1995)]. [1]: /lookup/doi/10.1126/science.270.5239.1189

Virus-induced immunosuppression: immune system-mediated destruction of virus-infected dendritic cells results in generalized immune suppression.

Abstract: Despite the clinical importance of virus-induced immunosuppression, how virus infection may lead to a generalized suppression of the host immune response is poorly understood. To elucidate the principles involved, we analyzed the mechanism by which a lymphocytic choriomeningitis virus (LCMV) variant produces a generalized immune suppression in its natural host, the mouse. Whereas adult mice inoculated intravenously with LCMV Armstrong rapidly clear the infection and remain immunocompetent, inoculation with the Armstrong-derived LCMV variant clone 13, which differs from its parent virus at only two amino acid positions, by contrast results in persistent infection and a generalized deficit in responsiveness to subsequent immune challenge. Here we show that the immune suppression induced by LCMV clone 13 is associated with a CD8-dependent loss of interdigitating dendritic cells from periarteriolar lymphoid sheaths in the spleen and, functionally, with a deficit in the ability of splenocytes from infected mice to stimulate the proliferation of naive T cells in a primary mixed lymphocyte reaction. Dendritic cells are not depleted in immunocompetent Armstrong-infected mice. LCMV Armstrong and clone 13 exhibit differences in their tropism within the spleen, with clone 13 causing a higher level of infection of antigen-presenting cells in the white pulp, including periarterial interdigitating dendritic cells, than Armstrong, thereby rendering these cells targets for destruction by the antiviral CD8+ cytotoxic T-lymphocyte response which is induced at early times following infection with either virus. Our findings illustrate the key role that virus tropism may play in determining pathogenicity and, further, document a mechanism for virus-induced immunosuppression which may contribute to the clinically important immune suppression associated with many virus infections, including human immunodeficiency virus type 1.

Mechanisms of immune suppression in patients with head and neck cancer: presence of CD34(+) cells which suppress immune functions within cancers that secrete granulocyte-macrophage colony-stimulating factor.

Abstract: Production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by murine tumors has been shown to induce immune suppressive cells having homology with GM progenitor cells. The purpose of this study was to determine if human head and neck cancers secrete GM-CSF, if this is associated with an intratumoral presence of similar cells expressing the hematopoietic progenitor cell antigen CD34, and if such CD34(+) cells suppress functions of intratumoral T cells. This was evaluated with fresh head and neck cancers, and in some instances regional lymph nodes and control tissue. Ten of the 14 squamous cell carcinomas (SCCs) studied secreted greater than 5 ng GM-CSF/g tissue. GM-CSF was not secreted in significant levels by either the other cancer types or by control normal muscle. Each of the high GM-CSF-secreting SCCs, but none of the cancers that did not secrete GM-CSF, contained cells expressing the hematopoietic progenitor cell antigen CD34 that had the capacity to grow into colonies in soft agar. Available regional lymph nodes from patients with high GM-CSF-producing cancers also contained CD34(+) cells. Depletion of CD34(+) cells from dissociated cancers increased interleukin 2 secretion by the intratumoral lymphocytes while addition of the CD34(+) cells to dissociated cancers reduced interleukin 2 production, indicating that the presence of CD34(+) cells within GM-CSF-producing head and neck SCCs results in suppressed functional competence of lymphocytes within the SCCs. These results show that GM-CSF-secreting SCCs contain cells expressing the hematopoietic antigen CD34 which are inhibitory to the capacity of lymphocytes within the SCCs to secrete interleukin 2.

T cell priming versus T cell tolerance induced by synthetic peptides

Abstract: It is well known that synthetic peptides are able to both induce and tolerize T cells. We have examined the parameters leading either to priming or tolerance of CD8+ cytotoxic T lymphocytes (CTL) in vivo with a major histocompatibility complex class I (H-2 Db) binding peptide derived from the glycoprotein (GP aa33-41) of lymphocytic choriomeningitis virus (LCMV). By varying dose, route, and frequency of LCMV GP peptide application, we found that a single local subcutaneous injection of 50-500 micrograms peptide emulsified in incomplete Freund's adjuvant protected mice against LCMV infection, whereas repetitive and systemic intraperitoneal application of the same dose caused tolerance of LCMV-specific CTL. The peptide-induced tolerance was transient in euthymic mice but permanent in thymectomized mice. These findings are relevant for a selective use of peptides as a therapeutic approach: peptide-induced priming of T cells for vaccination and peptide-mediated T cell tolerance for intervention in immunopathologies and autoimmune diseases.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats.

Abstract: The persistence of microchimerism in human whole organ recipients years or decades after transplantation (1, 2) reflects the migration long before of bone marrow-derived donor leukocytes from the allografts (3, 4). We have postulated that these immunocompetent donor cells represent one limb of initially antagonistic but ultimately attenuated or abrogated host-versus-graft (HVG,* rejection) and graft-versus-host (GVH) reactions (1-5) (Fig. 1). We describe here a study in rats of the HVG and GVH components of this two-way immunologic paradigm. The clinical and histopathologic expression of the two arms with and without immunosuppression was correlated with the quantity and quality of recipient tissue chimerism and with the development of donor-specific tolerance following transplantation from Lewis (LEW) donors to Brown Norway (BN) recipients of different organs (intestine, liver, heart, kidney) and of different free leukocyte suspensions (bone marrow, lymph nodes, spleen, thymus, and blood). Figure 1 Dualistic immune reactions of host-versus-graft (HVG) and graft-versus-host (GVH) in the two-way paradigm of transplantation immunology. Following the acute reaction, the evolution of tolerance of each leukocyte population to the other is seen as a low-grade ... Although the results leave numerous questions unanswered about basic mechanisms, they cast light on 4 issues that are relevant to planning of clinical tolerance induction protocols: (1) The relative risk of producing clinical GVHD with the tranplantation of different organs and with infusion of a standardized dose of leukocytes obtained from various lymphoid organs, (2) the relative tolerogenicity of the parenchymal organs and the leukocyte suspensions, (3) correlation of 1 and 2 with the density and lineage profile of the chimerism in recipient tissues and, (4) the relation to the quantity and lineage composition of chimerism to chronic rejection.

Granulocyte/macrophage colony-stimulating factor-stimulated hepatic dendritic cell progenitors prolong pancreatic islet allograft survival

Abstract: Hepatic allografts are accepted without immunosuppressive therapy when transplanted between many MHC-incompatible mouse strains and certain rat strains (1, 2). Moreover, transplants of the liver protect other organ grafts of the same donor or donor strain from rejection (3–7). It has been postulated that this inherent tolerogenicity of the liver—a comparatively leukocyte-rich organ compared with the kidney or heart—is a consequence of donor-recipient leukocyte interaction leading to long-lasting, mutual, immunologic unresponsiveness (8, 9). A corollary of this hypothesis is that failure to establish and maintain donor cell chimerism results in imbalanced donor-recipient cell interaction, which may lead to graft rejection. Possible effector mechanisms of this two-way paradigm have been suggested (10). However, a cellular and molecular basis for interactions that may predispose to the development of mutual, donor-recipient immunologic nonreactivity has not been elucidated. In the multilineage cell chimerism that has been described in recipient tissues following transplantation of the liver or other organs, donor-derived dendritic cells (DC*) known to migrate to secondary lymphoid tissue (11) have been featured prominently (1, 9, 12). Although the DC resident in normal lymphoid tissue are potent antigen-presenting cells (13), freshly-isolated DC from commonly transplanted non-lymphoid tissues, such as the liver, kidney, or heart, are functionally “immature” (13, 14). Their maturation is thought to reflect the up-regulation by cytokines of both MHC gene product and costimulatory molecule expression (15). It has been suggested (8, 16) that these costimulatory molecule-deficient DC may constitute potentially tolerogenic precursors of the chimeric leukocytes seen in organ graft recipients. The magnitude, tissue-specific site dependency, replicative capacity, or maturational stage of chimeric DC that might be necessary to mediate postulated tolerizing effects has not been established. Recently, we have succeeded in propagating DC progenitors from normal mouse liver in response to granulocyte/macrophage colony stimulating factor (GM-CSF) (17). Following local or systemic injection, these cells migrate to T-dependent areas of allogeneic host lymphoid tissue, and express cell surface donor MHC class II. They persist indefinitely, although in diminished numbers (18). Furthermore, in spontaneously tolerant liver transplant recipients (but not in animals rejecting donor strain hearts), donor-derived DC can be propagated from host bone marrow and spleen using GM-CSF (19). These observations have raised questions about the functional significance of GM-CSF-stimulated, donor-derived DC progenitors in allograft recipients, and their possible relation to liver tolerogenicity. The potential of exploiting these putative tolerogenic cells for the therapy of graft rejection has also been suggested (16, 17). In this study, we have examined whether systemic injection of GM-CSF-stimulated, liver-derived DC progenitors can affect the survival of subsequent (pancreatic islet) allografts from the same donor strain. The results show that the liver-derived cells, but not “mature” GM-CSF-stimulated spleen-derived DC, significantly prolong islet transplant survival. They suggest a possible role of donor-derived, GM-CSF-responsive DC progenitors in allograft acceptance that may be related to the inherent tolerogenicity of the liver.

Intra- and intermolecular spreading of autoimmunity involving the nuclear self-antigens la (ss-b) and ro(ss-a)

Abstract: We have tested the extent of immune self-tolerance to the ubiquitously expressed nuclear/cytoplasmic autoantigens La (SS-B) and Ro (SS-A) in healthy, nonautoimmune mice. Immunization of mice with recombinant mouse La resulted in a specific, isotype-switched autoantibody response, which was initially directed toward the La C subfragment (aa 111-242) but rapidly spread to involve the La A (aa 1-107) and La F (aa 243-345) regions of the La antigen. Intramolecular spreading of the anti-La antibody response was further demonstrated by the appearance of autoantibodies to multiple, nonoverlapping antigenic regions of La, after immunization of mice with the 107-aa La A subfragment. Moreover, immunization of mice with recombinant mouse or human La also elicited specific anti-60-kDa Ro IgG antibodies in all strains tested. Mice immunized with 60-kDa Ro produced a high titer anti-Ro antibody response, which was also associated with intermolecular spreading, resulting in the specific appearance of anti-La autoantibodies. These findings show that the development of autoantibodies to multiple components of the La/Ro ribonucleoprotein complex may follow initiation of immunity to a single component. In addition, the data reveal the incomplete nature of immune tolerance to La and Ro despite their endogenous expression in all nucleated cells. These observations are likely to account for the coexistence of anti-La/Ro antibodies in autoimmune disease and suggest a general explanation for the appearance of mixed autoantibody patterns in systemic autoimmune disorders.

Ex vivo coating of islet cell allografts with murine CTLA4/Fc promotes graft tolerance.

Abstract: To test the hypothesis that blockade of B7-triggered costimulation by donor cells could preclude allograft rejection, we coated crude islet allograft preparations in vitro for 1 h with a murine CTLA4/Fc fusion protein. Murine CTLA4/Fc blocks the proliferative response in primary mixed lymphocyte cultures (MLC) and Con A-stimulated murine spleen cell cultures by 85 to 95%. Responder cells from a primary MLC containing mCTLA4/Fc were hyporesponsive upon restimulation to the same stimulator cells in a secondary MLC lacking mCTLA4/Fc. Because of mutations in the Fc gamma RI and C'1q binding sites of the Fc portion of the murine CTLA4/Fc fusion protein, the molecule binds to, but does not target, cells for Ab-dependent cellular cytotoxicity or complement-directed cytolysis. Although systemic immunosuppression was not applied, 42% (10 of 24) of B6AF1 recipients of islet allografts pretreated with CTLA4/Fc were permanently engrafted. Further, 50% of hosts bearing functioning islet allografts more than 150 days post-transplant were formally proved to be tolerant to donor tissues. A persistent CD4+ and CD8+ T cell infiltrate surrounding, but not invading, islet grafts in tolerant hosts was discerned. In control experiments, 89% (8 of 9) of islet allografts coated with mIgG3, and 100% (n = 10) pretreated with media alone were rejected. Thus, we conclude that 1) B7-triggered costimulation by donor APCs is an important element of rejection, and 2) blockade of the B7 pathway by in vitro allograft manipulation is able to induce tolerance.

Microchimerism, Dendritic Cell Progenitors and Transplantation Tolerance

Abstract: The recent discovery of multilineage donor leukocyte microchimerism in allograft recipients up to three decades after organ transplantation implies the migration and survival of donor stem cells within the host. It has been postulated that in chimeric graft recipients, reciprocal modulation of immune responsiveness between donor and recipient leukocytes may lead, eventually, to the induction of mutual immunologic nonreactivity (tolerance). A prominent donor leukocyte, both in human organ transplant recipients and in animals, has invariably been the bone marrow-derived dendritic cell (DC). These cells have been classically perceived as the most potent antigen-presenting cells but evidence also exists for their tolerogenicity. The liver, despite its comparatively heavy leukocyte content, is the whole organ that is most capable of inducing tolerance. We have observed that DC progenitors propagated from normal mouse liver in response to GM-CSF express only low levels of major histocompatibility complex (MHC) class II antigen and little or no cell surface B7 family T cell costimulatory molecules. They fail to activate resting naive allogeneic T cells. When injected into normal allogeneic recipients, these DC progenitors migrate to T-dependent areas of host lymphoid tissue, where some at least upregulate cell surface MHC class II. These donor-derived cells persist indefinitely, recapitulating the behavior pattern of donor leukocytes after the successful transplantation of all whole organs, but most dramatically after the orthotopic (replacement) engraftment of the liver. A key finding is that in mice, progeny of these donor-derived DC progenitors can be propagated ex vivo from the bone marrow and other lymphoid tissues of nonimmunosuppressed spontaneously tolerant liver allograft recipients. In humans, donor DC can also be grown from the blood of organ allograft recipients whose organ-source chimerism is augmented with donor bone marrow infusion. DC progenitors cannot, however, be propagated from the lymphoid tissue of nonimmunosuppressed cardiac-allografted mice that reject their grafts. These findings are congruent with the possibility that bidirectional leukocyte migration and donor cell chimerism play key roles in acquired transplantation tolerance. Although the cell interactions are undoubtedly complex, a discrete role can be identified for DC under well-defined experimental conditions. Bone marrow-derived DC progenitors (MHC class II+, B7-1dim, B7-2-) induce alloantigen-specific hyporesponsiveness (anergy) in naive T cells in vitro. Moreover, costimulatory molecule-deficient DC progenitors administered systemically prolong the survival of mouse heart or pancreatic islet allografts. How the regulation of donor DC phenotype and function relates to the balance between the immunogenicity and tolerogenicity of organ allografts remains to be determined.

Interleukin‐2 Deficient Mice: A New Model to Study Autoimmunity and Self‐Tolerance

Abstract: Previous work revealed IL-2 as a key cytokine regulating the growth, differentiation and function of lymphocytes (for review see Smith 1988. Paul 1989). It is a glycoprotein of about 15 kD (Gillis et al. 1978) which mediates cell communications via a complex receptor system composed of three subunits. apy (for review see Taniguchi & Minami 1993. Kishimoto et al. 1994). Only the a-chain is specific for IL-2. the p-subunit is used also by IL-15 (Giri et al. 1994. Burton et al. 1994) and the y-subunit is used by IL-2, IL-4. IL-7. lL-9 and IL-15 (Noguchi et al. 1993, Russell et al. 1993. Kondo et al. 1993). Since IL-2 is considered as an indispensable factor for cytotoxic responses, it is used as an immunotherapeutic agent for the treatment of patients with disseminated cancers and with infectious diseases (Rosenberg 1988, Kaplan et al. 1991, Fauci 1993). However, the exact role of IL-2 in vivo is far from being understood. Its elucidation was hampered by a lack of suitable experimental systems that would allow to evaluate the pleiotropic activities of this interleukin in the context of the whole immune system. The technology of targeted mutagenesis in mouse germline developed in the laboratories of Capecchi and Smithies (Thomas & Capecchi 1989,

CD4+ but not CD8+ T cells are required for the induction of oral tolerance.

Abstract: It has been suggested that oral tolerance is mediated by CD8+ T lymphocytes, but the functional properties of these cells are unclear. Here we show that the induction of tolerance by feeding mice ovalbumin (OVA) does not prime antigen-specific class I MHC-restricted cytotoxic T cells in vivo. Indeed, such responses are markedly suppressed in mice fed OVA, and the induction of oral tolerance is abolished by depletion in vivo of CD4+ but not CD8+ T cells. These results indicate that CD8+ lymphocytes are unlikely to play a major role in the induction of oral tolerance and are the first demonstration that specific cytotoxic responses to an exogenous antigen can be suppressed by feeding antigen.

Fas (CD95) participates in peripheral T cell deletion and associated apoptosis in vivo

Abstract: Following exposure to some types of antigen (superantigens), responsive T cells expand and then decline in numbers, a phenomenon that has been called 'peripheral deletion'. This process may play a role in limiting autoimmune reactions and in the maintenance of immune homeostasis. Here we describe experiments on peripheral deletion in mice carrying the lpr/lpr defect, which has been shown to be due to defective production of the CD95/Fas molecule. Young lpr/lpr mice with no apparent immunologic abnormalities display a defect in bacterial superantigen-induced peripheral deletion. Apoptotic death of the expanded T cell population associated with such peripheral deletion. Apoptotic death of the expanded T cell population associated with such peripheral deletion in normal animals is dramatically reduced in the mutant mice. Further, the levels of Fas on responding cells in normal mice increases and decreases together with increases and decreases in cell numbers, suggesting that cells with the highest levels of Fas are preferentially deleted. These observations are consistent with the known ability of CD95 to transduce a signal leading to apoptosis, and they implicate this signal transduction pathway in peripheral deletion. In contrast, bacterial superantigen-induced deletion of thymocytes appears to be fully functional in these mice, and thus Fas/APO-1 does not appear to be required for this process. Further, antibody ligation of the TCR on activated T cells from normal or young lpr/lpr mice can induce apoptosis and therefore under some circumstances this phenomenon is not dependent upon CD95/Fas. Thus, to avoid autoreactivity and ensure immune homeostasis, several different apoptotic mechanisms exist in peripheral T lymphocytes, only some of which involve Fas.(ABSTRACT TRUNCATED AT 250 WORDS)

IL-12 as mediator and adjuvant for the induction of contact sensitivity in vivo.

Abstract: To determine whether IL-12 serves as a regulator of contact sensitivity reactions, mice were painted with either 1.0% trinitrochlorobenzene or 0.5% dinitrofluorobenzene on abdominal skin. At various time points thereafter, regional lymph nodes or spleens were prepared for RNA extraction, and the signals for IL-12 p35 and p40 chain were sought by quantitative reverse transcriptase-PCR. Time course analysis showed a constitutive expression of p35 chain mRNA signals throughout the experiment (0 to 72 h), whereas the signal for the p40 chain was transiently induced in lymph node and spleen cells after 12 to 14 h. Cellular depletion experiments and double label in situ hybridization studies showed that dendritic cells were sources for a major part of the p40 chain message. The presence of functional IL-12 in culture supernatants was indirectly assessed by addition of anti-IL-12 antiserum and analysis of IFN-gamma production. Significant amounts of IFN-gamma could only be detected in supernatants of allergen-treated animals. Addition of anti-IL-12 antiserum inhibited IFN-gamma production by about 55%. In a further attempt to assess the role of IL-12 in contact sensitivity, anti-IL-12 antiserum was injected i.p. into mice, and ear swelling responses were assessed following challenge. Injection of anti-IL-12 antiserum significantly reduced ear swelling responses by 85%. Thus anti-IL-12 treatment almost completely prevented sensitization. To assess whether IL-12 would be able to overcome in vivo tolerance, UV-tolerized animals were treated with i.p. IL-12 in a contact allergy system. Treatment of mice with IL-12 not only prevented tolerance induction, but was able to reverse UV-induced tolerance. In aggregate, our data point to an important role for IL-12 as a mediator and adjuvant for the induction of contact sensitivity in vivo.

Immunosuppressive mechanisms in semen: implications for contraception

Abstract: The immunosuppressive effects of human seminal plasma are mediated by several factors. The prostaglandins (PG) of the E series (PGE and 19-hydroxy PGE) predominate and raise intracellular cAMP in leukocytes. By this mechanism they suppress lymphocyte proliferation, natural killer (NK) cell activity and are likely to modify cytokine release from antigen presenting cells (APC). In this way, acquired and innate responses (including immune surveillance) in the reproductive tract will be curtailed, at least temporarily, after intercourse. Semen contains several inhibitors of complement and a unique reservoirs of CD59, a major complement inhibitor, is found on the prostasomes which are sub-micron organelles with lipid membranes. The prostasomes also inhibit lymphocyte proliferation and the activity of phagocytic cells. Other suppressive agents are also present in semen and may exert specific effects, for example, transforming growth factor-beta which may inhibit primed responses to antigen, and receptors for Fc fraction of gamma-globulin which might bind inflammatory agents. A thesis is proposed that the balance between maximum chances of survival for spermatozoa and minimum chances for micro-organisms has been disturbed by an increased use of non-barrier contraception, an increase in population mobility and sexual contact and the arrival of new diseases such as AIDS. A further major concern is that following infection of cells of the cervix with virus, repeated exposure to human seminal plasma may accelerate the progression of disease.

The role of epidermal cytokines in the generation of cutaneous immune reactions and ultraviolet radiation-induced immune suppression.

Abstract: For most of the past century scientists and physicians have recognized that UV rays present in sunlight have the potential to affect human health and well being adversely. Ultraviolet radiation is the primary cause of non-melanoma skin cancer. Exposure to UV induces sunburn and erythema, promotes premature aging of the skin and causes ocular damage, including cataract formation. In addition, exposure to UV radiation impairs the function of the immune system. In a pioneering set of experiments carried out by Kripke in the mid1970s, the association between the immunosuppressive effects of UV radiation and its carcinogenic potential was first recognized. Unlike the vast majority of murine tumors, a large proportion of skin tumors induced by UV exposure failed to grow progressively when transplanted to normal syngeneic immune-competent hosts. These “regressor” tumors would only grow progressively upon transfer to immune-compromised individuals. The explanation for this observation is that the UV-induced tumors are highly antigenic, they are recognized as foreign by the immune system of the host animal and are rejected. Thus, one observes tumor rejection when transplanted into immune-competent animals but progressive tumor growth in mice whose immune system is suppressed. How then did these regressor tumors grow progressively in the primary UV-irradiated host? In addition to inducing skin cancer, UV is also immune suppressive. Exposure to subcarcinogenic doses of UV suppresses the immune system of the autochthonous host, thus allowing the antigenic tumors to grow progressively. Subsequent studies by Kripke and coworkers and Daynes and colleagues demonstrated that exposure to subcarcinogenic doses of UV radiation suppressed the generation of cell-mediated immune reactions, in part by the induction of antigenic-specific suppressor T cells. These cells control both the development of the primary tumor in the UV-irradiated host and can transfer the tumor-susceptible state from UV-irradiated mice to normal age-matched syngeneic controls. Thus, these early studies in experimental animals established a link between the ability of UV to suppress the immune response and induce skin cancer.’J More recently a similar conclusion has been arrived at from studies with human volunteers. Ultraviolet exposure suppresses the induction of a contact hypersensitivity (CHS)* reaction in a proportion (40-50%) of normal human volunteer^^,^; however, in almost 100% of biopsyproven skin cancer patients, UV exposure suppresses the induction of an immune r e a ~ t i o n . ~ This finding suggests that the immune suppression generated by UV exposure is a major risk factor for skin cancer induction in both experimental animals and skin cancer patients. This observation has fueled the efforts of many to understand the mechanisms involved in the immune suppression induced by exposure to UV radiation. The focus of this report will be to review some of the more recent findings in the field, concentrating on the role of epidermal cytokines in both the enhancement and suppression of cutaneous immune reactions.

Adrenergic blockade ameliorates cellular immune responses to mental stress in humans.

Abstract: This study evaluated the sympathoadrenal modulation of behaviorally evoked immune responses by administration of a nonselective adrenoceptor antagonist (labetalol) to subjects exposed to mental stress. In a 2 x 2 factorial design, subjects were assigned to a labetalol or saline condition and, within each condition, were exposed either to acute laboratory stress or no stress (control). Lymphocyte subsets, natural killer (NK) cell cytotoxicity, and T cell proliferation to phytohemagglutinin and concanavalin A were assessed pre-experimentally, at baseline after infusion and after 18 minutes of mental stress (or rest). By comparison with the other three conditions, the saline-stress group showed a greater peripheral NK cell number and cytotoxicity, lower mitogenic response to phytohemagglutinin and concanavalin A, and diminished ratio of CD4:CD8 cells after the stressor. As predicted, immune responses did not differ among the remaining groups (labetalol-stress, saline-rest, labetalol-rest). Group differences in NK cell cytotoxicity were not significant after controlling for differences in NK cell numbers. These findings demonstrate that the occurrence of certain immunologic responses to acute psychological stress are dependent on concomitant activation of the sympathetic nervous system.

Mechanisms of acquired thymic tolerance in experimental autoimmune encephalomyelitis: thymic dendritic-enriched cells induce specific peripheral T cell unresponsiveness in vivo.

Abstract: Experimental autoimmune encephalomyelitis (EAE), an experimental model for the study of multiple sclerosis, is an autoimmune disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP). MBP-reactive CD4+ T cells, predominantly expressing the V beta 8.2 T cell receptor (TCR), migrate from the peripheral lymphoid organs and initiate the inflammatory response in the brain. We have previously shown that a single intrathymic injection of MBP or its major encephalitogenic peptide (p71-90), but not a nonencephalitogenic peptide (p21-40), induces antigen-specific systemic tolerance and inhibits the induction of EAE in Lewis rats. In this study, we investigated the mechanisms of induction and maintenance of acquired thymic tolerance in this model. First, we investigated which thymic cell is responsible for "induction" of systemic tolerance. Thymic dendritic-enriched cells, isolated by plastic adherence, when incubated in vitro with p71-90 and injected intravenously into Lewis rats, were capable of preventing the development of EAE, but his protection was lost in thymectomized recipients. In addition, intravenous injection of thymic dendritic cells isolated from animals that had been previously injected intrathymically with p71-90 but not p21-40 also prevented the development of EAE. Second, to determine the "effector" mechanisms involved in acquired thymic tolerance, we compared TCR expression in the brains of animals with actively induced EAE with TCR expression in animals that received intrathymic injection of p71-90 or p21-40. Using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) technique, we found increased expression of CD4 and V beta 8.2 message in brains of immunized animals compared with those of naive animals. In animals intrathymically injected with p71-90 but not p21-40, CD4 and V beta 8.2 transcript levels were significantly reduced compared with immunized controls. Immunohistologic studies of brain tissue and spleens with specific V beta 8.2 and control V beta 10 monoclonal antibodies confirmed these observations in vivo. These findings, taken together with recent data demonstrating that activated T cells circulate through the thymus, suggest that interaction of thymic dendritic cells with specific TCR of activated peripheral T cells can lead to inactivation of these antigen-specific cells and confirm the role of V beta 8.2-expressing T cells in EAE.

Comparison of the suppressive effects of interleukin-10 and interleukin-4 on synovial fluid macrophages and blood monocytes from patients with inflammatory arthritis.

Abstract: This study determined the potential capacity of interleukin-10 (IL-10), compared with IL-4, to control the production of tumour necrosis factor-alpha (TNF-alpha), IL-1 beta and IL-1 receptor antagonist (IL-1ra) and the expression of major histocompatibility complex (MHC) class II antigens by monocytes/macrophages isolated from synovial fluid of patients with rheumatoid or other forms of chronic inflammatory arthritis Mononuclear cells were isolated from synovial fluid and peripheral blood and incubated with or without lipopolysaccharide (LPS), and with or without IL-10 (100 U/ml, 10 ng/ml) or IL-4 (10 ng/ml) for 22 hr TNF-alpha, IL-1 beta and IL-1ra levels were measured by enzyme-linked immunosorbent assay (ELISA) in the culture supernatants, and MHC class II expression was examined on the monocytes/macrophages by flow cytometry IL-10, unlike IL-4, decreased TNF-alpha production by LPS-stimulated synovial fluid cells to the same extent as by LPS-stimulated peripheral blood cells from the same patients IL-10 and IL-4 suppressed equally IL-1 beta production by the same cells However, only IL-4 significantly increased IL-1ra production by synovial fluid mononuclear cells Synovial fluid cells expressed increased levels of MHC class II antigen, and these levels were not as efficiently suppressed by IL-10 as they were for peripheral blood cells Because IL-10 and IL-4 differentially regulate TNF-alpha and IL-1ra production by synovial fluid mononuclear cells, selective use of either IL-10 or IL-4 in the treatment of chronic inflammatory conditions will depend on whether TNF-alpha or IL-1, respectively, is established as primarily responsible for the maintenance of the chronic inflammatory condition

Lymphocytes selected in allogeneic thymic epithelium mediate dominant tolerance toward tissue grafts of the thymic epithelium haplotype

Abstract: Athymic mice grafted at birth with allogeneic thymic epithelium (TE) from day 10 embryos before hematopoietic cell colonization reconstitute normal numbers of T cells and exhibit full life-long tolerance to skin grafts of the TE haplotype. Intravenous transfers of splenic cells, from these animals to adult syngeneic athymic recipients, reconstitute T-cell compartments and the ability to reject third-party skin grafts. The transfer of specific tolerance to skin grafts of the TE donor strain, however, is not observed in all reconstituted recipients, and the fraction of nontolerant recipients increases with decreasing numbers of cells transferred. Furthermore, transfers of high numbers of total or CD4+ T cells from TE chimeras to T-cell receptor-anti-H-Y antigen transgenic immunocompetent syngeneic hosts specifically hinder the rejection of skin grafts of the TE haplotype that normally occurs in such recipients. These observations demonstrate (i) that mice tolerized by allogeneic TE and bearing healthy skin grafts harbor peripheral immunocompetent T cells capable of rejecting this very same graft; and (ii) that TE selects for regulatory T cells that can inhibit effector activities of graft-reactive cells.

Breakdown of B cell tolerance in a mouse model of systemic lupus erythematosus.

Abstract: Anti-DNA antibodies, specifically those that stain nuclei in a homogenous nuclear (HN) fashion, are diagnostic of systemic lupus erythematosus (SLE) and the MRL-lpr/lpr SLE murine model. We have used a heavy chain transgene that increases the frequency of anti-HN antibodies to address whether their production in SLE is the consequence of a defect in B cell tolerance. Anti-HN B cells were undetectable in nonautoimmune-prone transgenic mice, but in MRL-lpr/lpr transgenic mice their Ig was evident in the sera and they were readily retrievable as hybridomas. We conclude that nonautoimmune animals actively delete anti-HN-specific B cells, and that MRL-lpr/lpr mice are defective in this process possibly because of the lpr defect in the fas gene.

Resistance to herpes stromal keratitis conferred by an IgG2a-derived peptide.

Abstract: Not all peripheral tissue antigens enter the thymus and it is unclear how the immune system remains tolerant to this class of self antigen. As tolerance to self peptides can generate gaps in the T-cell repertoire for cross-reactive foreign antigens, we investigated whether this mechanism might also diminish autoimmune reactions to similar peptides expressed by peripheral tissues. Herpes stromal keratitis (HSK) is a virally induced autoimmune reaction against corneal tissues mediated by T cells, and is a leading cause of human blindness. Resistance to HSK in mice is associated with allotypic variation in immunoglobulin genes, possibly because circulating immunoglobin-derived peptides can cross-tolerize T cells specific for corneal tissue autoantigens. Here we show that HSK is mediated by T-cell clones specific for corneal self antigens which also recognize an allotype-bearing peptide derived from IgG2a, and that exposure of HSK-susceptible mice to a soluble form of this peptide confers resistance to HSK. Shared expression of peptide subsequences between sequestered tissue proteins and circulating proteins may be important for maintenance of self-tolerance and prevention of autoimmunity.