HUMAN CD100, A NOVEL LEUKOCYTE SEMAPHORIN THAT PROMOTES B-CELL AGGREGATION AND DIFFERENTIATION

Herein we describe the molecular characterization of the human leukocy te activation antigen CD100 and identify it as the first semaphorin, t o our knowledge, in the immune system. Semaphorins have recently been described as neuronal chemorepellants that direct pioneering neurons d uring nervous system development. In this study we demonstrate that CD 100 induces B cells to aggregate and improves their viability in vitro . We show that CD100 modifies CD40-CD40L B-cell signaling by augmentin g B-cell aggregation and survival and down-regulating CD23 expression. Thus, these results suggest that semaphorins as exemplified by CD100 also play a functional role in the immune system.