Local cell-associated immunity in the Peyer's patches of mouse intestines.

After oral infection of mice with a Salmonella strain, low numbers of organisms could be found in the Peyer's patches of the small intestine. In the course of a few days the organism in the Peyer's patches multiplied to about 10(5) and then were steadily eliminated so that by 10 days, very few organisms could be found in the lymphoid follicles. Because no organisms could be found in the spleen or other organs during this period, it is probable that the decline in numbers was due to killing of the organisms in situ. This development of antibacterial ability was not inhibited by treatment with cyclophosphamide, in contrast to the rapid growth of organisms which occurred in the spleen after intravenous injection in the presence of cyclophosphamide. The difference in behavior between Peyer's patches and the spleen upon treatment with cyclophosphamide is explained in terms of the extent of natural priming of Peyer's patches due to continual contact of the intestine with gram-negative enteric organisms. Once the spleen was primed, cyclophosphamide did not interfere with the elimination of a second challenge with the same organism.