INTRINSIC DIFFERENCES IN L-SELECTIN EXPRESSION LEVELS AFFECT T-LYMPHOCYTE AND B-LYMPHOCYTE SUBSET-SPECIFIC RECIRCULATION PATHWAYS

Lymphocyte migration into lymphoid organs is regulated by tissue-speci fic adhesion molecules such as L-selectin and the alpha(4) beta(7) int egrin, Whether L-selectin also regulates lymphocyte subset-specific mi gration into specific lymphoid tissues was examined in this study by c omparing the migration of CD4(+) T cells, CD8(+) T cells, and B cells from L-selectin-deficient and wild-type mice. T cells were the predomi nant lymphocyte subset entering PLN, MLN, Peyer's patches, and spleen during short term (l-h) migration assays. However, both B cell and CD4 (+) and CD8(+) T cell entries into PLN, MLN, and Peyer's patches were dramatically impaired (73-98%) by loss of L-selectin, Lymphocyte expre ssion of alpha(4) beta(7) integrin did not compensate for the loss of L-selectin, since both B and T cells predominantly migrated into the s pleen in the absence of L-selectin, The more efficient migration of T cells into peripheral lymphoid tissues relative to that of B cells was partly explained by the finding that T cells expressed L-selectin at 50 to 100% higher levels than B cells, In addition, a 50% reduction in L-selectin expression by lymphocytes from hemizygous L-selectin(+/-) mice resulted in a 50 to 70% decrease in short term lymphocyte migrati on into peripheral lymphoid tissues relative to that of wild-type lymp hocytes. Thus, the differential-migration of T and B lymphocyte subset s to lymphoid tissues is regulated in part by subset-specific differen ces in L-selectin expression levels.