Antigenic selection of IgG precursor subpopulations.

The temporal increase in the antigen-binding characteristic of the IgG antibody synthesized after primary immunization is thought to result from antigen preferentially selecting those precursors of the antibody-forming cells with higher affinity receptors. We have investigated this regulatory role of antigen on the selection and expression of IgG precursor subpopulations in rabbit lymph node populations undergoing the secondary anti-bovine serum albumin (BSA) response in vitro. The data indicate that although immunologic memory increased between 1 and 4 months after immunization there was not an increase in antigen sensitivity. We also determined the avidity of the IgG antibody secreted by PFC elicited in the cell cultures. Although the avidity of antibody secreted by PFC elicited with low concentrations of antigen was 2-fold greater than when high concentrations of antigen were employed, analyses of the avidity subpopulations of IgG PFC revealed that memory potential was not restricted to high affinity-primed cells. Moreover, populations of PFC that gave differing avidity values were similar in terms of their plaque diameters and IgG secretion rates.