D. Sean Riminton

B cell-intrinsic signaling through IL-21 receptor and STAT3 is required for establishing long-lived antibody responses in humans.

Engagement of cytokine receptors by specific ligands activate Janus kinase–signal transducer and activator of transcription (STAT) signaling pathways. The exact roles of STATs in human lymphocyte behavior remain incompletely defined. Interleukin (IL)-21 activates STAT1 and STAT3 and has emerged as a potent regulator of B cell differentiation. We have studied patients with inactivating mutations in STAT1 or STAT3 to dissect their contribution to B cell function in vivo and in response to IL-21 in vitro. STAT3 mutations dramatically reduced the number of functional, antigen (Ag)-specific memory B cells and abolished the ability of IL-21 to induce naive B cells to differentiate into plasma cells (PCs). This resulted from impaired activation of the molecular machinery required for PC generation. In contrast, STAT1 deficiency had no effect on memory B cell formation in vivo or IL-21–induced immunoglobulin secretion in vitro. Thus, STAT3 plays a critical role in generating effector B cells from naive precursors in humans. STAT3-activating cytokines such as IL-21 thus underpin Ag-specific humoral immune responses and provide a mechanism for the functional antibody deficit in STAT3-deficient patients.

Tumor necrosis factor: a master-regulator of leukocyte movement.

Abstract Tumor necrosis factor (TNF)-mediated activities are potentially numerous, although in TNF-deficient ( −/− ) mice, altered spatial orientation of leukocytes within tissues is the predominant phenotype. Here, we propose that TNF plays a fundamental role in the control of leukocyte movement by virtue of a pivotal role in regulation of chemokine expression.

Molecular Pathogenesis of EBV Susceptibility in XLP as Revealed by Analysis of Female Carriers with Heterozygous Expression of SAP

Analysis of females carriers of the X-linked lymphoproliferative (XLP) trait reveals the mechanism underlying exquisite sensitivity of XLP patients to often-fatal infection with the normally innocuous Epstein-Barr virus.

Membrane lymphotoxin contributes to anti-leishmanial immunity by controlling structural integrity of lymphoid organs

Lymphotoxin (LT)α in combination with LTβ forms membrane‐bound heterotrimeric complexes with a crucial function in lymph node (LN) organogenesis and correct morphogenesis of secondary lymphoid tissue. To study the role of membrane LT (mLT) in lymphoid tissue organogenesis we generated an LTβ‐deficient mouse strain on a pure genetic C57BL/6 background (B6.LTβ–/–) and compared it to a unique series of LTα‐, TNF‐ and TNF/LTα‐gene‐targeted mice on an identical genetic background (B6.LTα–/–, B6.TNF–/– and B6 TNF/LTα–/–). B6.LTβ–/– mice lacked peripheral LN with the exception of mesenteric LN, and displayed a disturbed micro‐architecture of the spleen, although less profoundly than LTα‐ or TNF/LTα‐deficient mice. Radiation bone marrow chimeras (B6.WT→B6.LTβ–/–) developed Peyers patch (PP)‐like lymphoid aggregates in the intestinal wall indicating a possible role for soluble LTα3 in the formation of the PP anlage. After infection with Leishmania major, B6.LTβ–/– mice developed a fatal disseminating leishmaniasis resulting in death after 8 to 14 weeks, despite the natural resistance of the C57BL/6 genetic background (B6.WT) mice to the parasite. Both, the cellular and the humoral anti‐L. major immune responses were delayed and ineffective. However, the expression pattern of the key cytokines IFN‐γ and IL‐12 were comparable in B6.WT and B6.LTβ–/– mice. Infection of radiation bone marrow chimeras showed that it is the LTβ‐dependent presence of lymphoid tissue and not the expression of mLT itself that renders mice resistant to leishmaniasis.

Expansion of somatically reverted memory CD8+ T cells in patients with X-linked lymphoproliferative disease caused by selective pressure from Epstein-Barr virus

In patients with XLP, a primary immunodeficiency caused by mutations in SH2D1A, EBV infection can lead to somatic reversion of the disease-causing mutation selectively in effector memory CD8 T cells; reverted CD8 cells are better able to respond to and kill EBV-infected cells.

Increased Thymic B Cells but Maintenance of ThymicStructure, T Cell Differentiation and Negative Selectionin Lymphotoxin-α and TNF Gene-Targeted Mice

TNF, lymphotoxin (LT) and their receptors are expressed constitutively in the thymus. It remains unclear whether these cytokines play a role in normal thymic structure or function. We have investigated thymocyte differentiation, selection and thymic organogenesis in gene targeted mice lacking LTalpha, TNF, or both (TNF/LTalpha-/-). The thymus was normal in TNF/LTalpha-/- mice with regard to cell yields and stromal architecture. Detailed analysis of alphabeta and gammadelta T cell-lineage thymocyte subsets revealed no abnormalities, implying that neither TNF nor LT play an essential role in T cell differentiation or positive selection. The number and distribution of thymic CD11c+ dendritic cells was also normal in the absence of both TNF and LTalpha. A three-fold increase in B cell numbers was observed consistently in the TNF/LTalpha-/- thymus. This phenotype was due entirely to the LTalpha deficiency and associated with changes in the hemopoietic compartment, rather than the thymic stromal compartment of LTalpha-/- mice. Finally, specific Vbeta8+ T cell deletion within the thymus following intrathymic injection of staphylococcal enterotoxin B (SEB) was TNF/LT independent. Thus, despite the presence of these cytokines and their receptors in the normal thymus, there appears no essential role for either TNF or LT in development of organ structure or for those processes associated with T cell repertoire selection.

Dermal Enhancement: Bacterial Products On Intact Skin Induce And Augment Organ-Specific Autoimmune Disease.

The skin is both an essential barrier for host defense and an important organ of immunity. In this study, we show that the application of cholera toxin to intact mouse skin induces and enhances autoimmune diseases affecting organs at distant anatomic sites, whereas its administration by the mucosal route has been reported to have the opposite effect. First, the CNS autoantigen myelin oligodendrocyte glycoprotein 35–55, when applied repeatedly with cholera toxin to the intact skin of healthy C57BL/6 mice, induced relapsing paralysis with demyelinating immunopathologic features similar to multiple sclerosis. Second, the application of cholera toxin in the absence of autoantigen exacerbated the severity of conventional experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein in CFA. Third, the application of cholera toxin to the intact skin of NOD/Lt mice, with or without insulin B peptide 9–23, exacerbated insulitis and T lymphocyte-derived IFN-γ and IL-4 production in the islets of Langerhans, resulting in an increased incidence and rate of onset of autoimmune diabetes. The data presented in this study highlight the different outcomes of adjuvant administration by different routes. Because dermal application of cholera toxin, and other bacterial products with similar adjuvant activities, is being developed as a clinical vaccination strategy, these data raise the possibility that it could precipitate autoimmune disease in genetically susceptible humans.

Autoimmunity in primary antibody deficiency is associated with protein tyrosine phosphatase nonreceptor type 22 (PTPN22)

BACKGROUND The 1858T allele of protein tyrosine phosphatase nonreceptor type 22 (PTPN22; R620W) exhibits one of the strongest and most consistent associations with sporadic autoimmune disease. Although autoimmunity is common in patients with primary antibody deficiency (PAD), it remains unknown whether its pathogenesis is similar when it arises in this context compared with in immunocompetent patients. OBJECTIVE We set out to determine whether the 1858T allele of PTPN22 was associated with PAD or with autoimmunity in the context of PAD. METHODS We genotyped rs2476601 (g.1858C>T), a single nucleotide polymorphism encoding substitution of arginine for tryptophan in PTPN22 (R620W), in 193 patients with PAD and 148 control subjects from an Australian cohort. We also performed a subgroup analysis according to the presence of autoimmunity and B-cell phenotypes. RESULTS C/T and T/T PTPN22 genotypes were more common in patients with PAD than in the matched control subjects (C/T, 18.1% vs 9.5%; T/T, 1.04% vs 0.6%). The T allele was associated with an increased risk of PAD relative to control subjects (odds ratio, 2.10; 95% CI, 1.11-4.00). The distribution of genotypes in control subjects was similar to those reported previously and did not deviate significantly from Hardy-Weinberg equilibrium. We found a strong association between the 1858T allele and PAD with coexistent autoimmune diseases. In patients with PAD and autoimmunity, 16 (43.2%) of 37 had at least one T allele of PTPN22 compared with 27 (17.3%) of 156 with the C/C genotype (P=.0014; odds ratio, 3.64; 95% CI, 1.68-7.88). We found no evidence that this effect was mediated by enrichment of CD21low B cells. CONCLUSION The 1858T PTPN22 allele is strongly associated with autoimmunity in patients with PAD.

TNFRSF13B Variants in SLE and Immunodeficiency

Background: The co-existence of autoimmunity and primary antibody deficiency in some individiuals is intriguing. The transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) gene (TNFRSF13B) has been implicated in both autoimmunity and primary antibody deficiency to varying extents in mice and humans. However, the phenotype described in mice with TNFRSF13B polymorphisms has not been entirely consistent with patients with similar orthologous polymorphisms.Objective: To further understand the relationship between TNFRSF13B variants and PAD and autoimmunity, we set out to determine the association of the two most common TNFRSF13B polymorphisms with autoimmunity and immunodeficiency, in patients with primary antibody deficiency and SLE.Method: We genotyped the C104R and A181E polymorphisms of TNFRSF13B in193 individuals and 144 controls from the Australian and New Zealand Antibody Deficiency Allele (ANZADA) Study, 107 patients from the Australian Point Mutation in Systemic Lupus Erythematosus (APOSLE) study, 169 patients with SLE from a European population, and 263 European controls. We were also able to determine TNFRSF13B genotypes for family members for nine of twelve pedigrees with primary antibody deficiency identified with TNFRSF13B variants.Results: The total number of TNFRSF13B variants in the primary antibody deficiency cohort was significantly higher than in the control group (p=0.0089; OR 9.481 [95% CI 1.218−73.81]). Similar results were obtained when patients with systemic lupus erythematosus were analysed. TNFRSF13B variants were strongly associated with SLE (p=0.0161, OR 3.316 [95% CI 1.245-8.836]). Familial analysis revealed incomplete penetrance of the TNFRSF13B variants.Conclusion: Taken together, the two most common TNFRSF13B variants are associated with primary antibody deficiency and systemic lupus erythematosus.

Sap is necessary for mediating antigen-specific effector functions of CD4+ AND CD8+ T cells

X-linked lymphoproliferative disease (XLP) is a rare immunodeficiency caused by mutations in SH2D1A which encodes SAP (SLAM-associated protein). SAP functions as an adaptor protein downstream of the SLAM family of cell surface receptors, thereby contributing to lymphocyte activation. The major defects in patients with XLP are exquisite sensitivity to infection with Epstein–Barr virus (EBV) due to dysfunctional CD8 + T cells and NK cells, and impaired antibody responses due to an inability of CD4 + T cells to provide ‘help’ to B cells for their differentiation into antibody secreting plasma cells. We have been investigating the molecular basis underlying these defects in XLP using a combination of approaches: by studying the viral specificity of CD8 + T cells from XLP patients as well as female carriers of XLP, and by studying the breakdown in CD4 + T cell help to B cells in an animal model of XLP (i.e., sap -deficient mice). Results from these studies highlight a critical role for interactions between SAP-associating receptors on T cells and appropriate antigen-presenting cells for the generation of effector CD4 + and CD8 + T cells and that this process is severely compromised in the presence of loss-of-function mutations in SH2D1A .