Induction of long-lived germinal centers associated with persisting antigen after viral infection

Vesicular stomatitis virus (VSV) induces an early T cell-independent neutralizing lgM response that is followed by a long-lived, T cell- dependent lgG response. We used the specific amplification factor of several 100x of VSV-virions for immunohistology to analyze the localization of VSV-specific B cells at different time points after immunization. At the peak of the IgM response (day 4), VSV-specific B cells were predominantly present in the red pulp and marginal zone but not in the T area. These B cells were mostly stained in the cytoplasm, characterizing them as antibody secreting cells. By day 6 after immunization, germinal centers (GC) containing surface-stained VSV- specific B cells became detectable and were fully established by day 12. At the same time, large VSV-specific B cell aggregates were present in the red pulp. High numbers of VSV-specific GC associated with persisting antigen were present 1 mo after immunization and later, i.e., considerably longer than has been observed for haptens. Some GC, exhibiting follicular dendritic cells and containing VSV-specific, proliferating B cells were still detectable up to 100 d after immunization. Long-lived GC were also observed after immunization with recombinant VSV-glycoprotein in absence of adjuvants. Thus some anti- virally protective (memory) B cells are cycling and locally proliferate in long-lived GC in association with persisting antigen and therefore seem responsible for long-term maintenance of elevated antibody levels. These observations extend earlier studies with carrier hapten antigens in adjuvant depots or complexed with specific IgG; they are the first to show colocalization of antigen and specific memory B cells and to analyze a protective neutralizing antibody response against an acute viral infection.