B cell responses to a peptide epitope. VIII. Immune complex-mediated regulation of memory B cell generation within germinal centers

Using an in vivo reconstitution assay, we examine here the role of immune c omplexes in both formation of germinal centers (GC) and processes that occu r subsequently within. The presence of Ag, as immune complexes, was found n ot to constitute a limiting requirement for the initiation of GC formation. No detrimental effect either on numbers or sizes of the resulting GC was o bserved when Ag-containing immune complexes were omitted during reconstitut ion. Thus, both recruitment and proliferation of Ag-activated Il cells with in GC appear not to be limited by Ag concentrations. In contrast, the prese nce of immune complexes was observed to be obligatory for the generation of Ag-specific memory B cells. This optimally required immune complexes to be constituted by IgG-class Abs with epitope specificities that were homologo us to those of the GC B cells, The GC reaction was also found to be charact erized by an enhancement of Ab specificity for the homologous epitope, Alth ough some improvement in specificity was noted in recall responses from imm une complex-deficient GC, the presence of appropriate immune complexes serv ed to further optimize the outcome, Here again, isotype and epitope-specifi city of the Ab constituent in immune complexes proved to be important.