CD40 is a cell surface receptor that belongs to the tumor necrosis factor-R (TNF-R) family, and that was first identified and functionally characterized on B lymphocytes. Its critical role in T cell-dependent humoral immune responses was demonstrated by patients with the hyper-IgM syndrome, as well as by gene targeting in mice. However, in recent years it has become clear that CD40 is expressed much more broadly, including expression on monocytes, dendritic cells, endothelial cells, and epithelial cells. In addition, the CD40-ligand (CD40-L/CD154), a member of the TNF family, is also expressed more widely than activated CD4+ T cells only. Therefore it is now thought that CD40-CD40-L interactions play a more general role in immune regulation. Collectively these studies have culminated in pre-clinical and clinical studies that are in progress. This article reviews recent developments in this field of research, with main emphasis on (1) structure and expression of CD40 and its ligand; (2) CD40 signal transduction; (3) in vitro function of CD40 on different cell types; and (4) in vivo functions of CD40/CD40-L interactions.

https://jlb.onlinelibrary.wiley.com/doi/pdf/10.1002/jlb.67.1.2

CD40-CD40 ligand.

Clinical spectrum of X-linked hyper-IgM syndrome

Cryptosporidium spp. are a major cause of diarrheal disease in both immunocompetent and immunodeficient individuals. They also cause waterborne disease in both the United States and United Kingdom. Studies on the mechanisms of immunity to cryptosporidiosis indicate the importance of the T-cell response. The spectrum and severity of disease in immunocompromised individuals with cryptosporidiosis reflect this importance since the most severe disease is seen in individuals with defects in the T-cell response. The most commonly studied group is that of patients with AIDS. These patients suffer from more severe and prolonged gastrointestinal disease that can be fatal; in addition, body systems other than the gastrointestinal tract may be affected. The widespread use of antiretroviral therapy does appear to be having a beneficial effect on recovery from cryptosporidiosis and on the frequency of infection in human immunodeficiency virus-positive patients. Other diseases that are associated with increased risk of severe cryptosporidiosis, such as primary immunodeficiencies, most notably severe combined immunodeficiency syndrome, are also predominantly associated with T-cell defects. Of the remaining groups, children with acute leukemia seem to be most at risk from cryptosporidiosis. There is less evidence of severe complications in patients with other malignant diseases or in those receiving immunosuppressive chemotherapy.

Epidemiology and Clinical Features of Cryptosporidium Infection in Immunocompromised Patients

The X-linked hyper-IgM syndrome: clinical and immunologic features of 79 patients.

Cryptosporidium is a protozoan parasite of medical and veterinary importance that causes gastroenteritis in a variety of vertebrate hosts. Several studies have reported different degrees of pathogenicity and virulence among Cryptosporidium species and isolates of the same species as well as evidence of variation in host susceptibility to infection. The identification and validation of Cryptosporidium virulence factors have been hindered by the renowned difficulties pertaining to the in vitro culture and genetic manipulation of this parasite. Nevertheless, substantial progress has been made in identifying putative virulence factors for Cryptosporidium. This progress has been accelerated since the publication of the Cryptosporidium parvum and C. hominis genomes, with the characterization of over 25 putative virulence factors identified by using a variety of immunological and molecular techniques and which are proposed to be involved in aspects of host-pathogen interactions from adhesion and locomotion to invasion and proliferation. Progress has also been made in the contribution of host factors that are associated with variations in both the severity and risk of infection. Here we provide a review comprised of the current state of knowledge on Cryptosporidium infectivity, pathogenesis, and transmissibility in light of our contemporary understanding of microbial virulence.

/pdf/cryptosporidium-pathogenicity-and-virulence-chfsignank.pdf

Cryptosporidium Pathogenicity and Virulence

We report an association between X-linked immunodeficiency with hyper-IgM (XHIM) and carcinomas affecting the liver, pancreas, biliary tree, and associated neuroectodermal endocrine cells. The tumors were fatal in eight of nine cases and in most instances were preceded by chronic cholangiopathy and/or cirrhosis. An additional group of subjects with XHIM had chronic inflammation of the liver or bile ducts but no malignancy. Many patients with XHIM were infected with cryptosporidia. CD40 is normally expressed on regenerating or inflammed bile duct epithelium. A CD40+ hepatocellular carcinoma cell line, HepG2, susceptible to cryptosporidia and CMV infection became resistant when cell surface CD40 was cross-linked by a CD40 ligand fusion protein. Apoptosis was triggered in HepG2 cells if protein synthesis was blocked by cycloheximide or if the cells were infected by cryptosporidia. Ligation of CD40 on biliary epithelium may contribute to defense against infection by intracellular pathogens. We propose that the CD40 ligand mutations that cause XHIM deprive the biliary epithelium of one line of defense against intracellular pathogens and that malignant transformation in the biliary tree follows chronic infection or inflammation. The resulting tumors may then progress without check by an effective immune response. Patients with XHIM who have abnormal liver function tests should be considered at increased risk for cholangiopathy or malignancy.

Cholangiopathy and tumors of the pancreas, liver, and biliary tree in boys with X-linked immunodeficiency with hyper-IgM.

Mice with disrupted genes for CD40 and CD40 ligand (CD40L) are unable to clear infection with Cryptosporidium parvum and develop cholangitis. Parasites are present in the gut, gall bladder, and biliary tree, and biliary epithelial cells express CD40 on the cell surface. SCID mice infected with C. parvum for >1 month can clear the infection after reconstitution with spleen cells from CD40, but not CD40L, knockout mice. In an in vitro model, C. parvum-infected HepG2 cells were triggered to apoptosis when incubated with a CD40L-CD8 fusion protein. The requirement for CD40-CD40L interactions for immunity to C. parvum indicated by our results may entail the triggering of apoptosis in infected cells, in addition to the known role of CD40L-CD40 interactions in stimulating cytokine production and promoting T-cell responses.

https://iai.asm.org/content/iai/66/2/603.full.pdf

Requirement for CD40-CD40 Ligand Interaction for Elimination of Cryptosporidium parvum from Mice

Although CD4 T cells are required for recovery from cryptosporidial infection, mice with severe combined immunodeficiency (SCID) remain infected for long periods without ill effect. In contrast, mice whose ability to use interferon(IFN)‐g is impaired, by neutralization or gene knockout, experience heavy cryptosporidial infection that may lead to death. To determine whether the innate immunity of SCID mice to Cryptosporidium parvum (CP) requires IFNg, doubly immunodeficient C57BL/6 SCID‐IFN-g knockout mice were bred. These mice experienced heavy CP infections of the gut; a significantly greater number became moribund or died, compared with mice carrying the SCID mutation alone or carrying disrupted IFNg genes alone. Mice with gene disruptions of inducible nitric oxide synthetase or Fas/Fas ligand recovered normally from CP infection. The results indicate that mice unable to produce specific immune responses because of the SCID mutation require IFN-g to avoid death after infection with CP. Cryptosporidium parvum (CP) is an apicomplexan parasite that infects epithelial cells in the intestine and the biliary tree. CP has attracted attention recently because it is difficult to eradicate from water supplies and can cause large outbreaks of infection. CP causes only transient diarrhea in healthy individuals, but it is responsible for severe enteritis and cholangitis in immunodeficient individuals, including individuals infected with AIDS. Experience in humans indicates that CD4 cells and an intact CD40‐CD154 pathway [1] are required for recovery from CP infections. These conclusions are confirmed in mice, where cytokine neutralization studies have identified interleukin (IL)‐12 and interferon (IFN)‐g as important or essential cytokines [2‐4]. Roles of these potentially separate effector mechanisms have been explored, in part, by infecting gene-knockout mice with CP. B6 mice with disrupted IFN-g genes have been

Interferon-γ Is Required for Innate Immunity to Cryptosporidium parvum in Mice

To clear a Cryptosporidium parvum infection, mice need CD4+ T cells, major histocompatibility complex class II, and an intact CD40-CD154 signaling pathway. CD40 is constitutively expressed on marrow-derived cells such as dendritic cells and B lymphocytes and is induced by gamma interferon (IFN-γ) on most somatic cells. To determine whether the CD40 needed to clear a C. parvum infection has to be on marrow-derived mononuclear cells or on the epithelial cells that normally harbor the parasite, we transplanted CD40−/− mice with CD40+/− bone marrow and then infected them with C. parvum. These chimeras cleared the C. parvum infection, while CD40+/− controls transplanted with CD40−/− marrow cells remained infected. CD40 expression on marrow-derived cells therefore suffices for a C. parvum infection to be cleared, while CD40 expression on intestinal epithelial cells is not sufficient. There was no difference between the acquisition of CD69 and CD154 by mesenteric lymph node T cells of C. parvum-infected animals with intact or disrupted CD40-CD154 pathways. CD4 T cells entered the intestinal laminae propriae of C. parvum-infected animals whether or not the CD40 genes of these recipients were intact. These results suggest that, for a C. parvum infection to be cleared, CD40 is not necessary for T-cell activation but may instead contribute to an effector pathway of marrow-derived cells.

Marrow-Derived CD40-Positive Cells Are Required for Mice To Clear Cryptosporidium parvum Infection

Staphylococcal enterotoxins are potentially valuable tools for investigating the development of T-cell responses because in experimental animals they can elicit either T-cell activation and proliferation or tolerance. Previous studies indicate that human T cells bearing the CD45RA phenotype (which account for the majority of newborn T cells) respond poorly to stimulation by staphylococcal enterotoxin B (SEB) compared with mature T cells from adult blood. The present studies show that the mean frequency of newborn T cells that proliferated in limiting dilution cultures stimulated by SEB was 1:3135, with a 1SD range of 3153-4191 compared with a mean of 1:493 and range of 120-1737 for adult T cells. Neither indomethacin nor the nitric oxide synthesis inhibitor, n-arginine methyl ester, increased SEB responses by newborn cells, arguing against down-regulation of the newborn response by prostaglandin or nitric oxide. Naive (CD45RA+) T cells from adult blood had a responder cell frequency to SEB similar to that of the newborn cells. IL-2 production by newborn cells was delayed compared with adult cells but was equivalent after 3 d of culture. Production of gamma-interferon and IL-4 was greater by adult than newborn cells. Our results indicate that a subset of CD45RA+ cells that is activated by SEB can mature to make IL-4 or gamma-interferon after 3-5 d. The limiting dilution assay results provide a quantitative basis for proliferation by naive T cells against which responses by T cells from healthy and premature newborns can be compared.

/pdf/proliferative-and-cytokine-responses-by-human-newborn-t-49nwn2ze80.pdf

Mary Cosyns

Papers

Cholangiopathy and tumors of the pancreas, liver, and biliary tree in boys with X-linked immunodeficiency with hyper-IgM.

Requirement for CD40-CD40 Ligand Interaction for Elimination of Cryptosporidium parvum from Mice

Interferon-γ Is Required for Innate Immunity to Cryptosporidium parvum in Mice

Marrow-Derived CD40-Positive Cells Are Required for Mice To Clear Cryptosporidium parvum Infection

Proliferative and cytokine responses by human newborn T cells stimulated with staphylococcal enterotoxin B.