T-CELLS WITHIN GERMINAL-CENTERS ARE SPECIFIC FOR THE IMMUNIZING ANTIGEN

A normal antibody response to T cell-dependent Ag requires physical co ntact between Ag-specific B and T cells. Because such Ag-specific cell s are rare in vivo, we sought to identify an in vivo site where they p hysically contact each other. We examined the Ag specificity of T cell s in germinal centers (GC) in lymph nodes, where it is known that Ag-s pecific B cells proliferate and mature. We investigated the Ag specifi city of GC T cells in situ by examining two characteristics: 1) expres sion of certain V(alpha) and V(beta) TCR families; and 2) incorporatio n of bromodeoxyuridine into T cell DNA after exposure to Ag as an inde x of Ag-induced proliferation. When GC were induced in mice with cytoc hrome c and myelin basic protein, the GC T cells were found to prefere ntially express V(alpha)11 and V(beta)8 TCR families, which are, respe ctively, the dominant TCR families in these two responses. Furthermore , GC T cells have proliferated upon exposure to the Ag that induced GC formation. Taken together, these results demonstrate that GC must rec ruit and retain Ag-specific T cells, thus implicating the GC as an in vivo site where Ag-specific T and B cells interact.