Selective Expansion of B Cells in Gut-Associated Lymphoid Tissues by Intestinal Microflora

Most B cells in rabbit lymphoid tissues express surface IgM with the V_Ha allotypes; a few B cells express surface IgM with the V_Ha-negative allotypes.  In the mutant strain of rabbits, ali/ali, nearly all B cells are V_Ha-negative for the first few weeks of life.  However, by 3 to 4 months of age, the B cell repertoire shifts so that approximately 50% of the B cells express the V_Ha allotypes.  We showed that this repertoire shift is not due to receptor editing, but instead, to the selective expansion of a small number of V_Ha allotype positive B cells.  Further, we showed that this repertoire shift requires gut-associated lymphoid tissues (GALT) and in particular, it requires the interaction between the intestinal microflora and GALT.   We hypothesize that one or more components of the intestinal microflora directly interacts with and stimulates V_Ha allotype positive B cells but not V_Ha-negative B cells; or, that the intestinal microflora induces an endogenous ligand that selectively stimulates V_Ha allotype positive B cells but not V_Ha allotype negative B cells.  We are testing this hypothesis by searching for a microbial, or GALT-induced ligand that selectively interacts with V_Ha-positive immunoglobulin (Ig) but not with V_Ha-negative Ig.   We are using affinity chromatography along with several molecular biology, immunohistology and biochemistry techniques to identify and characterize these ligands.