ANTIGEN RECEPTOR-INITIATED GROWTH-INHIBITION IS BLOCKED IN CD45-LOSS VARIANTS OF A MATURE B LYMPHOMA, WITH LIMITED EFFECTS ON APOPTOSIS

Role of CD45 in B cell antigen receptor (BcR)-mediated signaling events in mature B cells was examined using BAL-17 and its CD45-negative clones. In the CD45-negative clones, BcR stimulation induced tyrosine phosphorylation almost identical to the parental cells, with a few exceptions of reduced phosphorylation, especially of a protein of about 60 kDa. BcR-induced calcium responses were reduced in the CD45-negative clones, but the kinetics were similar to the parent. BcR stimulation led to growth inhibition in the parental cells, but signals for growth inhibition were completely blocked in the CD45-negative clones. Interestingly, the same stimulation induced low but significant levels of apoptosis both in the parent and in the CD45-negative clones. Thus, in mature BAL-17 cells, CD45 subtly mediates early signaling events (tyrosine phosphorylation and Ca2+ mobilization), and is absolutely required for the signaling pathway leading to growth regulation, but has limited effects on apoptosis.