T cells overexpressing interferon-gamma and interleukin-10 are found in both the thymus and secondary lymphoid tissues of feline immunodeficiency virus-infected cats

Similar to human immunodeficiency virus type 1, feline immunodeficiency vir us (FIV) replicates in the thymus of infected animals, causing marked alter ation in thymic lymphocyte subpopulations. The immune phenotype and cytokin e patterns in the thymus and secondary lymphoid tissues of FIV-infected cat s were investigated. FIV infection caused an acute-stage transient reductio n in CD4CD8 double-positive thymocytes, a marked increase in CD8 single-pos itive thymocytes, and formation of thymic B cell lymphoid follicles. Interf eron (IFN)-gamma and interleukin (IL)-10 mRNA were up-regulated in both the thymus and lymph nodes of FN-infected cats. Analysis of purified CD4 and C D8 cells revealed that CD4 cells produced most of the IL-10, whereas IFN-ga mma was produced by both subsets. Quantitative-competitive reverse-transcri ption polymerase chain reaction analysis revealed that thymocytes, especial ly CD4CD8 thymocytes, had much greater levels of gag mRNA than did lymph no de T cells. Thus, overexpression of IFN-gamma and IL-10 is a feature of the thymus and secondary lymphoid tissues of FIV-infected cats.