DIFFERENTIAL REQUIREMENTS OF CD45 FOR LYMPHOCYTE DEVELOPMENT AND FUNCTION

CD45 exon 6-deficient mice show a profound block of thymocyte developm ent at a transitional differentiation step from immature CD4(+) CD8(+) to mature single-positive cells. Only a few T lymphocytes are observe d in the periphery of such animals: but B cell development is not affe cted. We investigated whether mature B lymphocytes in CD45 exon B-defi cient mice have normal functions in the absence of CD45 expression and show here that CD45-defective B lymphocytes from CD45 exon 6-deficien t mice have intact B lymphocyte functions, including T-dependent and T -independent antigen-specific antibody production and class switching in vivo if normal CD4(+) T lymphocytes were adoptively transferred int o the mutant mice. From these results, we conclude that CD45 expressio n on B lymphocytes is not essential for B cell responses following ant igen stimulation in vivo. However, CD4(+) T helper function was severe ly diminished in CD45 exon 6-deficient mice, suggesting that the requi rements of CD45 molecules in antigen-specific response and development are different between T and B lymphocytes.