T-cells and HLA-class II expression in the large intestine of infants in the early postnatal period.

Background: There is only limited knowledge of the development of the immune responses of the gut in very young infants after exposure to bacterial and food antigens at birth.
Methods: In this study, 49 large intestinal biopsy specimens, which were judged to have normal morphology, were taken from 49 young infants. Eleven patients had Hirschsprung's disease (group 1) and 38 had miscellaneous conditions (group 2). The densities of T cells, their subsets expressing surface antigens CD8 and CD4, and T-cell receptors alpha/beta or gamma/beta were measured, as well as densities of mononuclear and epithelial cells expressing HLA-class II antigens.
Results: T-cell densities in groups 1 and 2 were similar. Patients with Hirschsprung's disease had significantly more HLA-DR (p = 0.006) and HLA-DP-expressing cells (p = 0.003) in the lamina propria than did the patients in group 2. In group 1, HLA-DR- (r = 0.58; p = 0.46) and HLA-DP-expressing cells (r = 0.66; p = 0.03) showed a significant positive regression with age in the lamina propria, whereas in group 2, HLA-DR+ cells in the lamina propria showed marked (r = -0.9; p = 0.006) negative regression during the first 1.5 months of life. In contrast to results in previous reports, in the current results, HLA-D region antigens were present in the epithelium in a considerable proportion (up to one fourth) of specimens from the large intestine in both groups. CD3+ (r = -0.59; p = 0.006) and CD4+ (r = -0.64; p = 0.002) cells showed a strong negative regression with age in the lamina propria during the first 2.5 months; and thereafter, there was a weak, insignificant rise in the numbers of these cells. The distribution of CD4+, CD8+, and TCR alpha/beta or gamma/beta T cells of the epithelium of the young infants did not differ significantly from that in the epithelium of adults.
Conclusions: These results show that several significant changes occur in the mucosal immune system during the first few weeks of life.