32 research outputs found
Increased Thymic B Cells but Maintenance of Thymic Structure, T Cell Differentiation and Negative Selection in 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 LTα, TNF, or both (TNF/LTα-/-). The thymus was normal in
TNF/LTα-/- mice with regard to cell yields and stromal architecture. Detailed analysis of αβ
and γδ 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
LTα. A three-fold increase in B cell numbers was observed consistently in the TNF/LTα-/-
thymus. This phenotype was due entirely to the LTα deficiency and associated with changes
in the hemopoietic compartment, rather than the thymic stromal compartment of LTα-/- mice.
Finally, specific Vβ8+ 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
Critical Points of Tumor Necrosis Factor Action in Central Nervous System Autoimmune Inflammation Defined by Gene Targeting
Tumor necrosis factor (TNF)–dependent sites of action in the generation of autoimmune inflammation have been defined by targeted disruption of TNF in the C57BL/6 mouse strain. C57BL/6 mice are susceptible to an inflammatory, demyelinating form of experimental autoimmune encephalomyelitis (EAE) induced by the 35–55 peptide of myelin oligodendrocyte glycoprotein. Direct targeting of a strain in which EAE was inducible was necessary, as the location of the TNF gene renders segregation of the mutated allele from the original major histocompatibility complex by backcrossing virtually impossible. In this way a single gene effect was studied. We show here that TNF is obligatory for normal initiation of the neurological deficit, as demonstrated by a significant (6 d) delay in disease in its absence relative to wild-type (WT) mice. During this delay, comparable numbers of leukocytes were isolated from the perfused central nervous system (CNS) of WT and TNF−/− mice. However, in the TNF−/− mice, immunohistological analysis of CNS tissue indicated that leukocytes failed to form the typical mature perivascular cuffs observed in WT mice at this same time point. Severe EAE, including paralysis and widespread CNS perivascular inflammation, eventually developed without TNF. TNF−/− and WT mice recovered from the acute illness at the same time, such that the overall disease course in TNF−/− mice was only 60% of the course in control mice. Primary demyelination occurred in both WT and TNF−/− mice, although it was of variable magnitude. These results are consistent with the TNF dependence of processes controlling initial leukocyte movement within the CNS. Nevertheless, potent alternative mechanisms exist to mediate all other phases of EAE
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
Molecular Pathogenesis of EBV Susceptibility in XLP as Revealed by Analysis of Female Carriers with Heterozygous Expression of SAP
X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency caused by mutations in SH2D1A which encodes SAP. SAP functions in signalling pathways elicited by the SLAM family of leukocyte receptors. A defining feature of XLP is exquisite sensitivity to infection with EBV, a B-lymphotropic virus, but not other viruses. Although previous studies have identified defects in lymphocytes from XLP patients, the unique role of SAP in controlling EBV infection remains unresolved. We describe a novel approach to this question using female XLP carriers who, due to random X-inactivation, contain both SAP+ and SAP− cells. This represents the human equivalent of a mixed bone marrow chimera in mice. While memory CD8+ T cells specific for CMV and influenza were distributed across SAP+ and SAP− populations, EBV-specific cells were exclusively SAP+. The preferential recruitment of SAP+ cells by EBV reflected the tropism of EBV for B cells, and the requirement for SAP expression in CD8+ T cells for them to respond to Ag-presentation by B cells, but not other cell types. The inability of SAP− clones to respond to Ag-presenting B cells was overcome by blocking the SLAM receptors NTB-A and 2B4, while ectopic expression of NTB-A on fibroblasts inhibited cytotoxicity of SAP− CD8+ T cells, thereby demonstrating that SLAM receptors acquire inhibitory function in the absence of SAP. The innovative XLP carrier model allowed us to unravel the mechanisms underlying the unique susceptibility of XLP patients to EBV infection in the absence of a relevant animal model. We found that this reflected the nature of the Ag-presenting cell, rather than EBV itself. Our data also identified a pathological signalling pathway that could be targeted to treat patients with severe EBV infection. This system may allow the study of other human diseases where heterozygous gene expression from random X-chromosome inactivation can be exploited
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-gamma 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
Dermal Enhancement: Bacterial Products on Intact Skin Induce and Augment Organ-Specific Autoimmune Disease
Adenovirus-induced liver pathology is mediated through TNF receptors I and II but is independent of TNF or lymphotoxin
Mice infected with an adenovirus mutant in which the E3 region is deleted, including TNF-resistance genes, develop fatal liver pathology within 3-4 days after infection. At least 10-fold more wild-type virus was needed to cause comparable pathology. These results indicate that the E3 region is critically involved in modulating the pathogenesis of adenovirus infection and that TNF may play a role in liver damage. To explore the latter possibility, the course of disease was examined in infected mice lacking TNFR-I and/or TNFRII, TNF only, or both TNF and lymphotoxin-α. Only mice lacking both TNFRI and TNFRII were protected from the lethal affects of the mutant adenovirus. Mice deficient in TNF or TNF and lymphotoxin-α displayed the fatal pathology. This outcome is consistent with the existence of another related ligand that binds TNFRI/II to mediate liver damage during infection with this mutant
Membrane lymphotoxin contributes to antileishmanial immunity by controlling structural integrity of lymphoid organs
Lymphotoxin (LT)alpha in combination with LTbeta 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 LTbeta-deficient mouse strain on a pure genetic C57BL/6 background (B6.LTbeta-/-) and compared it to a unique series of LTalpha-, TNF- and TNF/LTalpha-gene-targeted mice on an identical genetic background (B6.LTalpha-/-, B6.TNF-/- and B6 TNF/LTalpha-/-). B6.LTbeta-/- mice lacked peripheral LN with the exception of mesenteric LN, and displayed a disturbed micro-architecture of the spleen, although less profoundly than LTalpha- or TNF/LTalpha-deficient mice. Radiation bone marrow chimeras (B6.WT-->B6.LTbeta-/- developed Peyer's patch (PP)-like lymphoid aggregates in the intestinal wall indicating a possible role for soluble LTalpha(3) in the formation of the PP anlage. After infection with Leishmania major, B6.LTbeta-/- 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-gamma and IL-12 were comparable in B6.WT and B6.LTbeta-/- mice. Infection of radiation bone marrow chimeras showed that it is the LTbeta-dependent presence of lymphoid tissue and not the expression of mLT itself that renders mice resistant to leishmaniasis