RP105 IS ASSOCIATED WITH MD-1 AND TRANSMITS AN ACTIVATION SIGNAL IN HUMAN B-CELLS

RP105 was originally discovered as a mouse B-cell surface molecule tha t transmits an activation signal. The signal leads to resistance again st irradiation-induced apoptosis and massive B-cell proliferation. Rec ently, we found that mouse RP105 is associated with another molecule, MD-1. We have isolated here the human MD-1 cDNA. We show that human MD -1 is also associated with human RP105 and has an important role in ce ll surface expression of RP105, We also describe a monoclonal antibody (MoAb) that recognizes human RP105, Expression of RP105 is restricted to CD19(+) B cells. Histological studies showed that RP105 is express ed mainly on mature B cells in mantle zones. Germinal center cells are either dull or negative. RP105 is thus a novel human B-cell marker th at is preferentially expressed on mature B cells. Moreover, the anti-R P105 MoAb activates B cells, leading to increases in cell size, expres sion of a costimulatory molecule CD80, and DNA synthesis. The B-cell a ctivation pathway using RP105 is conserved in humans. (C) 1998 by The American Society of Hematology.