RESUMO
Expression of the CTLA-4 gene is absolutely required for immune homeostasis, but aspects of its molecular nature remain undefined. In particular, the characterization of the soluble CTLA-4 (sCTLA-4) protein isoform generated by an alternatively spliced mRNA of CTLA4 lacking transmembrane-encoding exon 3 has been hindered by the difficulty in distinguishing it from the transmembrane isoform of CTLA-4, Tm-CTLA-4. In the current study, sCTLA-4 has been analyzed using novel mAbs and polyclonal Abs specific for its unique C-terminal amino acid sequence. We demonstrate that the sCTLA-4 protein is secreted at low levels following the activation of primary human CD4(+) T cells and is increased only rarely in the serum of autoimmune patients. Unexpectedly, during our studies aimed to define the kinetics of sCTLA-4 produced by activated human CD4(+) T cells, we discovered that Tm-CTLA-4 is associated with microvesicles produced by the activated cells. The functional roles of sCTLA-4 and microvesicle-associated Tm-CTLA-4 warrant further investigation, especially as they relate to the multiple mechanisms of action described for the more commonly studied cell-associated Tm-CTLA-4.
Assuntos
Linfócitos T CD4-Positivos/metabolismo , Antígeno CTLA-4/metabolismo , Vesículas Citoplasmáticas/metabolismo , Glicoproteínas de Membrana/metabolismo , Adulto , Animais , Anticorpos Monoclonais/imunologia , Especificidade de Anticorpos/imunologia , Western Blotting , Antígeno CTLA-4/sangue , Antígeno CTLA-4/genética , Células Cultivadas , Vesículas Citoplasmáticas/ultraestrutura , Diabetes Mellitus Tipo 1/sangue , Feminino , Doença de Graves/sangue , Células HeLa , Humanos , Imunoensaio , Masculino , Glicoproteínas de Membrana/sangue , Glicoproteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Microscopia Imunoeletrônica , Pessoa de Meia-Idade , Isoformas de Proteínas/genética , Isoformas de Proteínas/imunologia , Isoformas de Proteínas/metabolismo , Solubilidade , Adulto JovemRESUMO
Numerous reports have demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) from individuals with a range of human autoimmune diseases, including type 1 diabetes, are deficient in their ability to control autologous proinflammatory responses when compared with nondiseased, control individuals. Treg dysfunction could be a primary, causal event or may result from perturbations in the immune system during disease development. Polymorphisms in genes associated with Treg function, such as IL2RA, confer a higher risk of autoimmune disease. Although this suggests a primary role for defective Tregs in autoimmunity, a link between IL2RA gene polymorphisms and Treg function has not been examined. We addressed this by examining the impact of an IL2RA haplotype associated with type 1 diabetes on Treg fitness and suppressive function. Studies were conducted using healthy human subjects to avoid any confounding effects of disease. We demonstrated that the presence of an autoimmune disease-associated IL2RA haplotype correlates with diminished IL-2 responsiveness in Ag-experienced CD4(+) T cells, as measured by phosphorylation of STAT5a, and is associated with lower levels of FOXP3 expression by Tregs and a reduction in their ability to suppress proliferation of autologous effector T cells. These data offer a rationale that contributes to the molecular and cellular mechanisms through which polymorphisms in the IL-2RA gene affect immune regulation, and consequently upon susceptibility to autoimmune and inflammatory diseases.
