Somatic Hypermutation in Peyers Patch Germinal centers and the Gut Environment

Germinal center (GC) reaction and somatic mutation in the spleen in response to protein antigens is absolutely dependent on help from antigen specific CD4+ T lymphocytes and stimulation of B cells via the CD19 co-receptor. However, the absence of CD4 T cell help apparently does not abrogate the GC formation in the Peyers patch. The present study makes use of normal, CD4-null and CD19-null mice to test the hypothesis that activation of somatic mutation in P. patch is independent of conventional co-stimulation. It was determined that the GC formation in the P. patches was dependent on help from alpha beta T cells and that gamma delta T cells were not involved in providing this help. Adoptive transfer of the splenic T cells from CD4-null mice into T deficient mice resulted in GC formation in the P. patch but not in the spleen. Therefore, the presence of GC in the P. patch of CD4-null mice was not due to a special T cell population but a function of the unique gut environment, since the splenic T cells can provide the requisite help for GC formation when present in the P. patch. It is apparent that obligatory stimuli for splenic GC formation and somatic mutation are dispensable in P. patches.