Intestinal microflora and diversification of the rabbit antibody repertoire

The rabbit establishes its primary Ab repertoire by somatically diversifyin g an initial repertoire that is limited by restricted V-H gene segment usag e during VDJ gene rearrangement. Somatic diversification occurs in gut-asso ciated lymphoid tissue (GALT), and by about 1-2 mo of age nearly all Ig VDJ genes are somatically diversified. In other species that are known to esta blish their primary Ab repertoire by somatic diversification, such as chick en, sheep, and cattle, diversification appears to be developmentally regula ted: it begins before birth and occurs independent of exogenous factors. Be cause somatic diversification in rabbit occurs well after birth in GALT, th e diversification process may not be developmentally regulated, but may req uire Interaction with exogenous factors derived from the gut. To test this hypothesis, we examined Ab repertoire diversification in rabbits in which t he appendix was ligated shortly after birth to prevent microbial colonizati on and all other organized GALT was surgically removed. We found that by 12 wk of age nearly 90% of the Ig VDJ genes in PBL were undiversified, indica ting that intestinal microflora are required for somatically diversifying t he Ab repertoire. We also examined repertoire diversification in sterilely derived remote colony rabbits that were hand raised away from contact with conventional rabbits and thereby acquired a different gut microflora, In th ese remote colony rabbits, GALT was underdeveloped, and 70% of the Ig VDJ g enes in PBL were undiversified, We conclude that specific, currently uniden tified intestinal microflora are required for Ab repertoire diversification .