289. Comparison of lymphocyte subsets and function in the rat and mouse testis

Testicular leukocytes are assumed to be involved in immunological surveillance against infection and tumours as well as regulation of local immune responses. They are implicated in mechanisms that make the testis a successful site for tissue transplantation in both rats and mice. Our previous studies using multi-colour fluorescence flow cytometric analysis to examine isolated testicular leukocytes in the rat testis have established the existence of a significant population of predominantly CD8+ T cells and a comparable number of lymphocytes expressing natural killer (NK) cell markers (NK and NKT cells). The functional activity of these testicular NK and NKT cells subsequently has been confirmed by a standard flow cytometric cytotoxicity assay using an NK-sensitive tumour cell line (YAC-1) and an NKT-sensitive tumour cell line (U937). Similar analyses of mouse testicular leukocytes have shown a slightly different pattern. The data indicate that mouse testicular lymphocytes comprise T cells, NK cells, and NKT cells, similar to the rat testis. However, while the apparent numerical densities of T cells in rat and mouse testes were similar, the numbers of NK and NKT cells were considerably lower in the mouse. Mouse testicular NKT cells were positive for staining with the tetramer CD1d/αGC, which is used to identify classical NKT cells, whereas rat NKT cells did not stain for this marker. Moreover, the CD8/CD4 T cell ratio in the mouse testis displayed a skewing towards the CD4+ subset. These data highlight the possibility that the immunological environment, and hence the course of immunological events, might be quite different in the testes of the two species. The reasons for these differences are not clear, however they should be taken into account when considering studies of testicular immune processes. Finally, comparative studies of immunological process in the testes of rats and mice may be very informative.