Elevated expression of Pgp-1 (Ly-24) by murine peritoneal B lymphocytes.

B cell expression of the surface glycoprotein, Pgp-1 (Ly-24), was evaluated using flow cytometric analysis. Pgp-1 expression on naive, conventional (splenic) B cells was low but could be increased by mitogenic stimulation. Pgp-1 expression on naive peritoneal B cells was higher than expression by unmanipulated conventional B cells, suggesting the possibility that peritoneal B cells have been activated in vivo. However, the elevated expression of Pgp-1 by peritoneal B cells was not accompanied by increased expression of surface Ia but was correlated with Ly-1 status. Further, Pgp-1 expression by B cells from germ-free mice did not differ from that of normal animals. The elevated expression of Pgp-1 by peritoneal B cells is superficially similar to that provoked by mitogenic stimulation of conventional B cells; however, several characteristics suggest that the elevated expression of Pgp-1 by peritoneal B cells does not reflect prior activation of these cells.