Calyculin A inhibits expression of CD8 alpha but not CD4 in human peripheral blood T cells

The CD8 glycoprotein serves as a coreceptor for T cell receptor (TCR)-media ted recognition of peptides associated to MHC class I. In CD8 alpha deficie ncy, MHC class-I restricted cytotoxic T lymphocytes (CTL) are absent and li neage commitment to CD8 cells is impaired. We described a pharmacological a pproach to reduce the amount of CD8 surface glycoproteins on human peripher al blood T cells. Using calyculin A, a potent inhibitor of protein phosphat ases, we were able to down regulate both CD8 alpha protein and mRNA. Reduct ion of CD8 alpha surface expression was dose- and time-dependent. The effec t was specific to CD8 alpha in that CD4 expression was not affected and spe cific for calyculin A. Okadaic acid, another phosphatase inhibitor did not show any influence on the expression of CD4 or CD8.