THE ASSOCIATION OF GUT-ASSOCIATED LYMPHOID-TISSUE AND BACTERIAL TRANSLOCATION IN THE NEWBORN RABBIT

The authors have previously demonstrated spontaneous bacterial translo cation (BT) in newborn rabbits and its resolution with aging. It is hy pothesized that this spontaneous BT was associated with an immature gu t-associated lymphoid tissue (GALT). The aim of the present study was to characterize the cellular populations of the GALT in rabbits at var ious ages and to correlate this with the frequency of BT. Small bowel (SB) sections and mesenteric lymph nodes (MLN) were harvested and cult ured (aerobically) from New Zealand White rabbits at 0, 6, 14, 28, and more than 90 days of age for determination of bacterial colonization (BC) and BT. Portions of ileum (n = 6 for each age) were simultaneousl y harvested for immunoperoxidase staining. Total T cells (CD5(+)), exp ressed as the number of positive cells/1,000 nuclei and activated T ce lls (CD25(+)), expressed as the number of positive cells/1000 nuclei a nd as the ratio of CD25(+)/CD5(+) cells, were analyzed for each tissue . Positive cells were counted in 30 villi by light microscopy. The inc idence of BT rose as BC increased in the small bowel and peaked at 6 d ays of age; BT then decreased with age. CD5(+) cells in the small bowe l villi at 0 days of age were few (2.5(+) positive cells/1000 nuclei) and the number significantly increased with age (6 days, 6.5; 14 days, 19.0: 28 days, 31.6; adult, 136.6 positive cells/1,000 nuclei). The d istribution of T cells started in the crypts. and with advancing age, cells were found all the way to the top of the villi. The number of CD 25(+) cells in the villi increased with age. The CD25(+)/CD5(+) ratio in the small bower villi peaked at 6 days of age. These results demons trate an inverse relationship between the number of CD5(+) cells in th e intestinal villi and the incidence of bacterial translocation. The e levation of activated T cells (CD25+) at 6 days of age may be the resu lt of an immunologic activation during the time of peak bacterial tran slocation. These data suggest that maturity of the GALT leads to a los s of spontaneous bacterial translocation in the newborn period. Modali ties that supplement the GALT may help reduce bacterial translocation. Copyriqht (C) 1996 by W.B. Saunders Company.