RESUMO
The homeostasis of the immune response requires tight regulation of the proliferation and apoptosis of activated lymphocytes. In humans, defects in immune homeostasis result in lymphoproliferation disorders including autoimmunity, haemophagocytic lymphohystiocytosis and lymphomas. The X-linked lymphoproliferative syndrome (XLP) is a rare, inherited immunodeficiency that is characterized by lymphohystiocytosis, hypogammaglobulinaemia and lymphomas, and that usually develops in response to infection with Epstein-Barr virus (EBV). Mutations in the signalling lymphocyte activation molecule (SLAM)-associated protein SAP, a signalling adaptor molecule, underlie 60% of cases of familial XLP. Here, we identify mutations in the gene that encodes the X-linked inhibitor-of-apoptosis XIAP (also termed BIRC4) in patients with XLP from three families without mutations in SAP. These mutations lead to defective expression of XIAP. We show that apoptosis of lymphocytes from XIAP-deficient patients is enhanced in response to various stimuli including the T-cell antigen receptor (TCR)-CD3 complex, the death receptor CD95 (also termed Fas or Apo-1) and the TNF-associated apoptosis-inducing ligand receptor (TRAIL-R). We also found that XIAP-deficient patients, like SAP-deficient patients, have low numbers of natural killer T-lymphocytes (NKT cells), indicating that XIAP is required for the survival and/or differentiation of NKT cells. The observation that XIAP-deficiency and SAP-deficiency are both associated with a defect in NKT cells strengthens the hypothesis that NKT cells have a key role in the immune response to EBV. Furthermore, by identifying an XLP immunodeficiency that is caused by mutations in XIAP, we show that XIAP is a potent regulator of lymphocyte homeostasis in vivo.
Assuntos
Transtornos Linfoproliferativos/genética , Transtornos Linfoproliferativos/patologia , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/deficiência , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/genética , Adulto , Apoptose , Sequência de Bases , Criança , Pré-Escolar , Feminino , Homeostase , Humanos , Lactente , Transtornos Linfoproliferativos/imunologia , Masculino , Mutação/genética , Linhagem , Linfócitos T Reguladores/imunologia , Linfócitos T Reguladores/patologiaRESUMO
It is well established that autoreactive B cells undergo negative selection. This stands in paradox with the high frequency of so-called natural autoreactive B cells producing low affinity polyreactive autoantibodies with recurrent specificities, suggesting that these B cells are selected on the basis of their autoreactivity. We previously described two transgenic mouse lines (with and without IgD) producing a human natural autoantibody (nAAb) that binds ssDNA and human Fcgamma. In the absence of human IgG, nAAb-transgenic B cells develop normally. By crossing these mice with animals expressing knockin chimeric IgG with the human Fcgamma, we now show that the constitutive expression of chimeric IgG promotes the increase of nAAb-expressing B cells. This positive selection is critically dependent on the presence of IgD, occurs in the spleen, and concerns all mature B cell subsets, with a relative preferential enrichment of marginal zone B cells. These data support the view that soluble self-Ags can result in positive clonal selection.
Assuntos
Autoantígenos/imunologia , Subpopulações de Linfócitos B/citologia , Subpopulações de Linfócitos B/imunologia , Animais , Autoanticorpos/biossíntese , Autoanticorpos/genética , Autoantígenos/biossíntese , Subpopulações de Linfócitos B/metabolismo , Diferenciação Celular/genética , Diferenciação Celular/imunologia , Células Cultivadas , Anergia Clonal/genética , Epitopos de Linfócito B/fisiologia , Humanos , Imunidade Inata/genética , Imunoglobulina D/biossíntese , Imunoglobulina D/genética , Imunoglobulina G/genética , Imunoglobulina G/fisiologia , Imunoglobulina M/biossíntese , Imunoglobulina M/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Receptores de Antígenos de Linfócitos B/fisiologia , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/fisiologia , Solubilidade , Baço/citologia , Baço/imunologia , Baço/metabolismoRESUMO
Under non-autoimmune conditions, rheumatoid factor (RF) B cells coexist peacefully with their antigen (IgG), or can be transiently activated during secondary immune responses because they can present xenoantigens to specific T cells captured in immune complex form. Such a situation should lead to affinity maturation of RF B cells and potentially dangerous production of high-affinity RF. We used two lines of transgenic mice expressing a somatically mutated pathological human RF in presence (IgM and IgD) or in absence (IgM only) of surface IgD, and confirm that RF B cell tolerance can result from an antigen-induced specific, but incomplete, deletion of naive RF B cells after antigen encounter. This deletion mainly concerns immature, transitional B cells. On the contrary, mature, IgM- and IgD-expressing RF B cells are resistant to such a deletion. These IgM and IgD RF B cells are functional and activable through both B cell receptor dependent (anti-IgM) and independent (LPS) pathways, but they are not fully responsive to human IgG either in vivo or in vitro. Taken together, these results suggest that another mechanism could be involved in the silencing of mature naive IgM and IgD RF B cells.