Heterogeneity of the BALB/c antiphosphorylcholine antibody response at the precursor cell level

Immune responsiveness to phosphorylcholine (PC) in BALB/c mice was characterized by combining (a) usage of highly sensitive radioimmunoassays for quantitation of antibody, heavy chain class, and idiotype on a weight basis; (b) isolation of PC specific B cells in fragment cultures; and (c) stimulation in a carrier primed environment with the PC hapten coupled to carrier through a tripeptide spacer in order to maximize carrier recognition. The specificity and accuracy of the radioimmunoassays were verified by specific inhibition, lack of nonspecific binding, and excellent concordance of values for monoclonal antibody concentration obtained independently for Fab and idiotype content. The latter evidence also serves as strong confirmation of the monoclonality of in vitro monofocal responses as well as the preservation of the idiotype on antibodies of differing immunoglobulin classes. The results indicate that while B cells expressing the TEPC 15 plasmacytoma idiotype predominate, other idiotypes may be represented by 2-50% of PC specific precursors, and monoclonal antibodies even of the TEPC 15 idiotype are produced in both the IgM and IgG1 immunoglobulin classes. These findings are confirmed by the analysis of serum antibodies produced in carrier primed mice immunized with hapten coupled through a tripeptide spacer, thus reemphasizing the enhancement of primary responsiveness, particularly IgG1 production, by maximizing carrier recognition. The finding of idiotype diversity in the PC response, as well as diversity of expression in terms of quantity and immunoglobulin class of antibody synthesized by the clonal progeny of B cells within the TEPC 15 clonotype emphasize the heterogeneity of the B cell population both in terms of the specificity repertoire and the physiological state of cells even within a single clonotype.