Switch in the protein tyrosine phosphatase associated with human CD100 semaphorin at terminal B-cell differentiation stage

Human CD100, the first semaphorin identified in the immune system, is a tra nsmembrane protein involved in T-cell activation. In the present study, we showed that activation of peripheral blood or tonsillar B lymphocytes induc ed the expression of CD100 in CD38(+)CD138(-) cell populations, including i n CD148(+) subpopulations, thus expressing a memory B-cell-like phenotype, Using an in vitro enzymatic assay, we found that protein tyrosine phosphata se (PTP) activities were immunoprecipitated with CD100 in these cell popula tions, which were isolated by cell sorting, as well as in most B-cell lines representing various stages of B-cell differentiation. Immunodepletion and Western blotting experiments demonstrated that CD45 was the PTP associated with CD100 in cell lines displaying pre-B, activated B, and pre plasma cel l phenotypes. CD45 also accounted for PTP activity immunoprecipitated with CD100 in CD38(+)CD138(-) cells sorted after activation of peripheral blood or tonsillar B lymphocytes. In contrast, no CD100-CD45 association was obse rved in plasma cell lines corresponding to the terminal B-cell differentiat ion stage, CD148, the other transmembrane PTP known to be implicated in lym phocyte signaling pathways, was either only partly involved in the CD100-as sociated PTP activity or not expressed in plasma cell fines, indicating the association of CD100 with another main PTP, Our data show that CD100 is di fferentially expressed and can functionally associate with distinct PTPs in B cells depending on their activation and maturation state. They also prov ide evidence for a switch in the CD100-associated PTP at terminal stage of B-cell differentiation. (C) 2000 by The American Society of Hematology.