%0 Journal Article %J J Immunol %D 2000 %T The role of B7 costimulation in CD4/CD8 T cell homeostasis. %A Yu, X %A Fournier, S %A Allison, J P %A Sharpe, A. H. %A Hodes, R J %K Animals %K Antigens, CD %K Antigens, CD28 %K Antigens, CD80 %K Antigens, CD86 %K Antigens, Differentiation %K CD4-CD8 Ratio %K CD4-Positive T-Lymphocytes %K CD8-Positive T-Lymphocytes %K CTLA-4 Antigen %K Down-Regulation %K Homeostasis %K Hyperplasia %K Immunoconjugates %K Lymphocyte Activation %K Lymphoid Tissue %K Membrane Glycoproteins %K Mice %K Mice, Congenic %K Mice, Inbred BALB C %K Mice, Inbred C57BL %K Mice, Mutant Strains %K Mice, Transgenic %K Phenotype %K Receptors, Antigen, T-Cell %K Receptors, Antigen, T-Cell, alpha-beta %K T-Lymphocyte Subsets %X The effect of B7-mediated costimulation on T cell homeostasis was examined in studies of B7-1 (CD80) and B7-2 (CD86) transgenic as well as B7-deficient mice. B7 overexpression in transgenic mice resulted in marked polyclonal peripheral T cell hyperplasia accompanied by skewing toward an increased proportion of CD8 single-positive cells and a decreased proportion of CD4 single-positive cells in thymus and more markedly in peripheral T cells. B7-induced T cell expansion was dependent on both CD28 and TCR expression. Transgenic overexpression of B7-1 or B7-2 resulted in down-regulation of cell surface CD28 on thymocytes and peripheral T cells through a mechanism mediated by intercellular interaction. Mice deficient in B7-1 and B7-2 exhibited changes that were the reciprocal of those observed in B7-overexpressing transgenics: a marked increase in the CD4/CD8 ratio in peripheral T cells and an increase in cell surface CD28 in thymus and peripheral T cells. These reciprocal effects of genetically engineered increase or decrease in B7 expression indicate that B7 costimulation plays a physiological role in the regulation of CD4+ and CD8+ T cell homeostasis. %B J Immunol %V 164 %P 3543-53 %8 2000 Apr 1 %G eng %N 7 %1 http://www.ncbi.nlm.nih.gov/pubmed/10725709?dopt=Abstract