B lymphocytes from hyporesponsive SJL mice contain aberrant nucleoside binding sites

Abstract

C8-substituted guanine ribonucleosides activate B cells by a novel pathway that apparently is independent of GTP-binding proteins and protein kinase C. B lymphocytes from SJL mice are hyporesponsive to antigen-independent inductive signals transmitted by these nucleosides. In the current studies, the basis for this observation was explored. Responses of normal murine strains to these agents have been dissociated into antigen-independent (inductive) and antigen-dependent (differentiative) types by use of the 7,8-disubstituted guanine ribonucleosides. Dose-response profiles for inductive responses appear to correlate with apparent K d values for low-affinity nucleoside binding sites; dose-response curves for antigen-dependent differentiative responses correlate with apparent K d values for high-affinity binding sites. It was found that the SJL low-affinity site exhibits an apparent K d that is approximately 10- to 20-fold lower in affinity for 8BrGuo than that of normal CBA mice. Although the low-affinity site in normal murine strains displays nearly equivalent affinity toward C8-substituted and 7,8-disubstituted nucleosides, the low-affinity site of SJL mice binds 7,8-disubstituted compounds with approximately 5-fold higher affinity than it does monosubstituted compounds. The dissociation constant for high-affinity nucleoside binding sites of SJL mice was only slightly different from that of CBA mice, consistent with the observation of essentially normal antigen-dependent nucleoside-mediated activity in SJL mice. The current observations support (a) a role for low-affinity binding sites in antigen-independent inductive events, (b) a role for high-affinity binding sites in antigen-dependent differentiative events mediated by substituted guanine nucleosides, and (c) the existence of aberrant low-affinity binding sites in B cells from SJL mice.