Showing papers by "Francis R. Carbone published in 2006"

The dominant role of CD8+ dendritic cells in cross-presentation is not dictated by antigen capture

Abstract: Mouse spleens contain three populations of conventional (CD11chigh) dendritic cells (DCs) that play distinct functions. The CD8+ DC are unique in that they can present exogenous antigens on their MHC class I molecules, a process known as cross-presentation. It is unclear whether this special ability is because only the CD8+ DC can capture the antigens used in cross-presentation assays, or because this is the only DC population that possesses specialized machinery for cross-presentation. To solve this important question we examined the splenic DC subsets for their ability to both present via MHC class II molecules and cross-present via MHC class I using four different forms of the model antigen ovalbumin (OVA). These forms include a cell-associated form, a soluble form, OVA expressed in bacteria, or OVA bound to latex beads. With the exception of bacterial antigen, which was poorly cross-presented by all DC, all antigenic forms were cross-presented much more efficiently by the CD8+ DC. This pattern could not be attributed simply to a difference in antigen capture because all DC subsets presented the antigen via MHC class II. Indeed, direct assessments of endocytosis showed that CD8+ and CD8− DC captured comparable amounts of soluble and bead-associated antigen, yet only the CD8+ DC cross-presented these antigenic forms. Our results indicate that cross-presentation requires specialized machinery that is expressed by CD8+ DC but largely absent from CD8− DC. This conclusion has important implications for the design of vaccination strategies based on antigen targeting to DC.

Systemic activation of dendritic cells by Toll-like receptor ligands or malaria infection impairs cross-presentation and antiviral immunity

Abstract: The mechanisms responsible for the immunosuppression associated with sepsis or some chronic blood infections remain poorly understood. Here we show that infection with a malaria parasite (Plasmodium berghei) or simple systemic exposure to bacterial or viral Toll-like receptor ligands inhibited cross-priming. Reduced cross-priming was a consequence of downregulation of cross-presentation by activated dendritic cells due to systemic activation that did not otherwise globally inhibit T cell proliferation. Although activated dendritic cells retained their capacity to present viral antigens via the endogenous major histocompatibility complex class I processing pathway, antiviral responses were greatly impaired in mice exposed to Toll-like receptor ligands. This is consistent with a key function for cross-presentation in antiviral immunity and helps explain the immunosuppressive effects of systemic infection. Moreover, inhibition of cross-presentation was overcome by injection of dendritic cells bearing antigen, which provides a new strategy for generating immunity during immunosuppressive blood infections.

Bone marrow-derived cells expand memory CD8+ T cells in response to viral infections of the lung and skin

Abstract: While naive CD8(+) T cells have been shown to require bone marrow-derived dendritic cells (DC) to initiate immunity, such a requirement for memory CD8(+) T cells has had limited assessment. By generating bone marrow chimeras that express the appropriate antigen-presenting molecules on either radiation-sensitive bone marrow-derived or radiation-resistant non-bone marrow-derived compartments, we showed that both primary and secondary immune responses to influenza virus infection of the lung were initiated in the draining LN. This required cells of bone marrow origin, most likely DC, for optimal expansion within the secondary lymphoid compartment. This was similarly the case with HSV-1 infection of the skin. As Langerhans cells are radioresistant, unlike other DC populations, these studies also demonstrate that the radiosensitive DC responsible for secondary expansion of HSV-specific memory are not Langerhans cells.

NKT cells are not critical for HSV-1 disease resolution

Abstract: NKT cells are a minor subset of T cells that have important roles in controlling immune responses in disease states including cancer, autoimmunity and pathogenic infections. In contrast to conventional T cells, NKT cells express an invariant TCR and respond to glycolipids presented by CD1d. In this study, we sought to investigate the role of NKT cells in regulating the response to infection with HSV-1, and the mechanism involved, in well-established mouse models. Previous studies of HSV-1 disease in mice have shown clear roles for CD4+ and CD8+ T cells. The role of NKT cells in the resolution of HSV-1 (KOS strain) infection was investigated through flank zosteriform or footpad infection in wild-type versus CD1d-deficient mice, by measurement of viral plaque-forming units at different sites after infection, lesion severity and HSV-1-specific T-cell responses. In contrast to a previous study using a more virulent strain of HSV-1 (SC16 strain), no differences were observed in disease magnitude or resolution, and furthermore, the T-cell response to HSV-1 (KOS strain) was unaltered in the absence of NKT cells. In conclusion, this study shows that NKT cells do not play a general role in controlling the resolution or severity of HSV-1 infection. Instead, the resolution or severity of the infection may depend on the HSV-1 strain under investigation.

CD4+ T Cells Can Protect APC from CTL-Mediated Elimination

Abstract: Professional APC play a central role in generating antiviral CD8 + CTL immunity. However, the fate of such APC following interaction with these same CTL remains poorly understood. We have shown previously that prolonged Ag presentation persists in the presence of a strong CTL response following HSV infection. In this study, we examined the mechanism of survival of APC in vivo when presenting an immunodominant determinant from HSV. We show that transferred peptide-labeled dendritic cells were eliminated from draining lymph nodes in the presence of HSV-specific CTL. Maturation of dendritic cells with LPS or anti-CD40 before injection protected against CTL lysis in vivo. Furthermore, endogenous APC could be eliminated from draining lymph nodes early after HSV infection by adoptive transfer of HSV-specific CTL, yet the cotransfer of significant virus-specific CD4 + T cell help promoted prolonged Ag presentation. This suggests that Th cells may assist in prolonging class I-restricted Ag presentation, potentially enhancing CTL recruitment and allowing more efficient T cell priming.

CTL response compensation for the loss of an immunodominant class I-restricted HSV-1 determinant

Abstract: The T-cell response to even complex pathogens is often focused on only a handful of immunodominant determinants. Such narrow responses provoke a selective pressure that can drive the emergence of CTL escape variants, raising the question of whether a broader response, targeting multiple non-dominant peptides may be more beneficial. To examine the ability of the T-cell repertoire to respond to non-dominant determinants, we have investigated how mutating the dominant peptide in HSV affects the magnitude of the CD8 + T-cell response. We found that the CTL response to HSV lacking the dominant peptide was only modestly reduced compared with the wild-type virus and, surprisingly, this compensation occurred without any enhancement in the response to an established minor epitope. These findings are supportive of a malleable T-cell repertoire that can elicit strong responses to alternate, unknown determinants in the absence of the dominant response.

Cutting edge: central memory T cells do not show accelerated proliferation or tissue infiltration in response to localized herpes simplex virus-1 infection.

Abstract: Memory T cells mount an enhanced response to secondary infections. Such an enhancement has been attributed in part to the ability of memory cells to more rapidly respond to cognate stimulation. In this study we have examined the rapidity with which murine CD8 + memory T cells respond to a localized infection with HSV. Although central memory T cells (TcM), but not the effector memory T cells, mounted a strong recall response to secondary infection, the kinetics of TcM proliferation, the magnitude of their expansion, and their infiltration into infected nonlymphoid tissues were not advanced compared with that observed for naive T cells. These findings imply that it is the lack of accelerated proliferation kinetics and the subsequent delayed dissemination into the periphery that limits the ability of TcM to rapidly control localized virus replication.