Bacterial translocation from the gastrointestinal tract of athymic (nu/nu) mice

The immune system may be one host defense mechanism preventing viable indigenous bacteria from translocating from the mouse gastrointestinal lumen to the mesenteric lymph nodes, spleen, liver, or kidney. The role of T-cell-dependent immunity in preventing bacteria from translocating from the gastrointestinal tract was tested with congenitally athymic nude (nu/nu) mice, heterozygous (nu/+) mice, and thymus-grafted nude (nu/nu) mice. Viable bacteria were cultured from 50% of the mesenteric lymph nodes, spleens, livers, and kidneys of athymic (nu/nu) mice, whereas heterozygous (nu/+) mice exhibited viable bacteria in only 5.2% of these organs. Both aerobic and strictly anaerobic bacteria were cultured from these organs with Escherichia coli and Lactobacillus predominanting. Grafting thymuses to the athymic (nu/nu) mice restored their immunological responses to sheep erythrocyte antigens. The incidence of bacterial translocation from the gastrointestinal tract was reduced from 50% in the athymic (nu/nu) mice to 7.8% in the thymus-grafted (nu/nu) mice. Thus, T-cell-dependent immunity restored by thymic grafts inhibited the translocation of certain indigenous bacteria from the gastrointestinal tract to the spleen, liver, and kidney in nu/nu mice.