THE EFFECT OF ADULT THYMECTOMY ON IMMUNE-RESPONSE TO INFECTION WITH LISTERIA-MONOCYTOGENES IN MICE

The role of adult thymus in in vivo immune response to infection with Listeria monocytogenes was examined using euthymic mice and adult-thymectomized (ATx) mice which had been thymectomized 2 weeks before. Numbers of T cells in peritoneal cavities and spleens were increased at 2 weeks after inoculation of L. monocytogenes, whereas such increases of T cells were several times higher in euthymic mice than in ATx mice. In flow-cytometric analysis of peritoneal exudate cells, a significant increase of CD3+CD4-CD8- cells bearing gamma/delta type T cell receptor was noted in euthymic mouse after infection compared to ATx mouse. Neither assay of antigen-specific T cell proliferation nor analysis of cell cycle exhibited any superiority of T cells obtained from euthymic mice to those obtained from ATx mice. These findings suggest that the enlargement of T cell population in euthymic mice is attributed largely to T cells which emigrate from the thymus after inoculation of L. monocytogenes. Moreover, in vivo protective immune response against secondarily challenged L. monocytogenes was achieved more efficiently in euthymic mice than in ATx mice, as shown by the clearance of the bacteria from organs and the survival rate of infected mice. Our results indicate the importance of adult thymus-dependent increase of T cells in eliminating the facultative intracellular bacteria such as L. monocytogenes.