Intestinal Microflora and Diversification of the Rabbit Antibody Repertoire

Abstract

The rabbit establishes its primary Ab repertoire by somatically diversifying an initial repertoire that is limited by restricted V H gene segment usage during VDJ gene rearrangement. Somatic diversification occurs in gut-associated 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 establish their primary Ab repertoire by somatic diversification, such as chicken, sheep, and cattle, diversification appears to be developmentally regulated: it begins before birth and occurs independent of exogenous factors. Because somatic diversification in rabbit occurs well after birth in GALT, the diversification process may not be developmentally regulated, but may require interaction with exogenous factors derived from the gut. To test this hypothesis, we examined Ab repertoire diversification in rabbits in which the appendix was ligated shortly after birth to prevent microbial colonization 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, indicating that intestinal microflora are required for somatically diversifying the 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 these remote colony rabbits, GALT was underdeveloped, and 70% of the Ig VDJ genes in PBL were undiversified. We conclude that specific, currently unidentified intestinal microflora are required for Ab repertoire diversification. The Journal of Immunology, 2000, 165: 2012-2019.T he rabbit is one of a few vertebrate species known to make limited use of combinatorial joining of multiple V H, D H , and J H gene segments during Ig heavy chain gene rearrangement. Although there are more than 100 V H gene segments available within the rabbit Ig heavy chain locus, many of which appear to be potentially functional (1), the 3Ј-most V H gene segment, V H 1, is utilized in 80 -90% of VDJ gene rearrangements (2). Most of the remaining 10 -20% of VDJ gene rearrangements utilize only two other V H gene segments, V H x and V H y (3). Rabbit B cells diversify their VDJ genes in gut-associated lymphoid tissue (GALT) 4 at 1-2 mo of age through two targeted mutational processes: a somatic gene conversion-like mechanism that transfers tracts of nucleotide sequence from upstream V H gene segment donors into the rearranged V H gene segment (4), and somatic hypermutation that distributes point mutations throughout the entire VDJ gene (5-7). At that time, the B cell population is also expanded through proliferation in GALT. B cell proliferation and Ig VDJ gene diversification in GALT results in a large population of B cells that express a wide range of Ab specificities.Several studies have established the importance of GALT in B cell proliferation and VDJ gene diversification. Weinstein et al. (7), for example, determined VDJ gene nucleotide...

New trends in rabbit feeding: influence of nutrition on intestinal health. A review

“…Rothkötter et al (1994) found, in germ free pigs, that the maturity of the immune system at 45-d was similar to that of normal 5-d old pigs, concluding that the stimulation of bacterial flora, as well as the presence of food antigens, is necessary for a normal development of the GALT. A number of reviews, both in rabbit (Knight and Winstead, 1997;Lanning et al, 2000) and in humans (Kelly et al, 2005), indicate that the presence of saprophyte flora and, possibly of some specific genera, can be crucial for the development of the primary repertoire.…”

Activation-induced deaminase cloning, localization, and protein extraction from young VH-mutant rabbit appendix

“…After birth, B cells with rearranged genes migrate into gut-associated lymphoid tissue such as the appendix. Gut microflora are required for B cells to proliferate and develop in appendix follicles (3). At Ϸ3 wk of age, diversification of rearranged gene sequences by GC and SHM starts within the appendix-follicle microenvironment (2).…”

Effect of palm oil and soya bean oil on growth performance and health of rabbit before and after weaning

“…It has even been shown in rabbits with ligated cecal appendix at birth (not contact with the intestinal contents) that the diversification of VDJ genes almost disappeared at 12 weeks old. The genesis of this primary repertoire would be dependent on exogenous factors (Lanning et al 2000). The good performance of the batch containing soya bean oil would be linked to the feed composition of this batch (mainly fatty acid profile of soya bean oil).…”

“…The symbiotic microflora of the digestive tract of the rabbit ensures microbial digestion and is also implicated in the digestive health of its host. It provides a protection against potentially pathogenic micro-organisms, stimulates the host immunity and diversification of the repertoire of antibodies (Lanning et al 2000;Guarner and Malagelada 2003). However, the low-growth rates observed at the first week after weaning for the two batches of rabbits are linked to the stress of weaning and the increase ingested solid compared with milk.…”