THE CYTOPLASMIC DOMAIN OF CD8-BETA REGULATES LCK KINASE ACTIVATION AND CD8 T-CELL DEVELOPMENT

Previous studies have shown that CD8 beta plays a role in both enhanci ng CD8 alpha-associated Lck kinase activity and promoting the developm ent of CDS-lineage T cells. To examine the role of this enhancement in the maturation of CD8-lineage cells, we assessed CD8 alpha-associated Lck kinase activity in both T cell hybridomas and thymocytes of mice expressing CD8 beta mutations known to impair CD8 T cell development. Lack of CD8 beta expression or expression of a cytoplasmic domain-dele ted CD8 beta resulted in a severalfold reduction in CD8 alpha-associat ed Lck kinase activity compared with that observed with cells expressi ng wild-type CD8 beta chain. This analysis indicated a critical role f or the cytoplasmic domain of CD8 beta in the regulation of CD8 alpha-a ssociated Lck activity, Decreased CD8 alpha-associated Lck activity ob served with the various CD8 beta mutations also correlated with dimini shed in vivo cellular tyrosine phosphorylation. In addition, analysis of CD8 beta mutant mice (CD8 beta(-/-) or cytoplasmic domain-deleted C D8 beta transgenic) indicated that the degree of reduction in CD8 alph a-associated Lck activity associated with each mutation correlated wit h the severity of developmental impairment. These results support the importance of CD8 beta-mediated enhancement of CD8 beta-associated Lck kinase activity in the differentiation of CD8 single-positive thymocy tes.