Regional variation in the proliferative rate and lifespan of alpha beta TCR+ and gamma delta TCR+ intraepithelial lymphocytes in the murine small intestine.

Using double staining for T-cell receptor (TCR) and 5-bromo-2'-deoxyuridine (BRdU) we have examined the proliferation rates and lifespan of murine intraepithelial lymphocytes (IEL's) in vivo. After a 24-hr pulse of BRdU the number of labelled alpha beta TCR+ IEL was significantly higher in the ileum than the duodenum. In contrast, incorporation of BRdU into gamma delta TCR+ IEL was significantly higher in the duodenum than the ileum. This regional variation was also seen after a 4-hr pulse of BRdU indicating that the differences probably reflect local rates of proliferation in the epithelium. Over a 6-day labelling period, the accumulation of labelled alpha beta TCR+ and gamma delta TCR+ IEL was linear, which allowed IEL lifespan to be calculated. There was considerable variation between groups of mice but the 50% population renewal time for alpha beta TCR+ IEL was 12-36 days in the duodenum and 9-11 days in the ileum, and for gamma delta TCR+ IEL was 12-21 days in the duodenum and 26-100 days in the ileum. The incorporation of BRdU into V beta 8+ IEL showed the same regional variation as alpha beta TCR+ IEL and the V delta 4 population behaved like the total gamma delta TCR+ IEL population. In contrast V beta 11+, potentially self-reactive IEL, showed a regional pattern of labelling like gamma delta TCR+ IEL. Incorporation of BRdU into both alpha beta TCR+ and gamma delta TCR+ IEL in germ-free mice was very low and did not show marked regional variation. alpha beta TCR+ and gamma delta TCR+ IEL from both proximal and distal bowel were cytotoxic. Therefore alpha beta TCR+ and gamma delta TCR+ IEL show different rates of division in different sections of the gut, perhaps reflecting responses to different antigens. Both alpha beta TCR+ and gamma delta TCR+ IEL reside in the epithelium for weeks during which time the gut epithelial population will have been renewed many times.