Antigen-specific and -non-specific regulatory influences of antibody in immune responses are determined by variable region properties.

The regulatory effects of a constant titre of anti-sheep erythrocyte (SRBC) antibodies collected during primary and secondary responses and separated according to class, as well as monoclonal antibodies of the same isotypes, were compared by studying the specific and total plaque-forming cell (PFC) responses to the simultaneous administration of antigen. Polyclonal secondary IgG1 antibodies were found unique in their ability to suppress completely specific PFC responses. Polyclonal secondary antibodies of other IgG subclasses, polyclonal primary IgG1 and monoclonal IgG1 antibodies, all were found at the same titre either totally ineffective or mediating very litte suppression. Primary polyclonal IgM antibodies were also found much superior to monoclonal antibodies and to secondary polyclonal IgM antibodies in their ability to enhance specific responses and largely augment the total number of Ig PFC in the spleen. While these results are most easily interpreted by postulating a primary determination of regulatory properties by V-regions, we could not find evidence for "allotype-restriction" of these effects.