The ontogeny of B lymphocytes IV. Induction signals mediating phenotypic conversion of PC.1⁻ to PC.1⁺B cells

Abstract

Abstract The present study presents evidence that spleen and lymph node cell populations contain a distinct subpopulation of B lymphocytes amounting to < 1 % of the total, which are committed and poised to the expression of the PC. 1 alloantigen, and which can be triggered in vitro to express PC.1. The pheno‐type of the PC.l‐inducible cells has been determined as Ig + Ia + complement receptor (CR) + PC.l − which characteristically is associated with mature lymphocytes. Since the PC.l alloantigen identifies plasmacytes, the induction experiments imply that the latter cells are in principle descendents of CR + B lymphocytes. The induction signal mediating PC.l − to PC.1 + conversion is different from that mediating early pro‐B cell induction. Inducing agents of PC.l − ←PC.1 + include carbamylcholine, thymopoietin, prostaglandin F 2α and 8‐bromo cyclic GMP, all of which have previously been shown to inhibit early pro‐B cell induction. Conversely, most agents inducing phenotype conversion in early pro‐B cells ( e.g. lipopolysaccharide, tumor‐necrotizing serum, isoproterenol, prostaglandin E 1 and dibutyryl cyclic AMP) are strong inhibitors of PC. 1 induction. The results suggest that inducible B lymphocytes are under dual control of agents imparting opposing signals to them, but that the mode in which they respond is reversed when they have matured to the CR + state. Since PC. 1 expression coincides largely with differentiation to antibody‐forming cells, the reversal of responses to regulatory signals may be of significance as a safeguard against spurious activation of B lymphocytes.