Depletion and repopulation of lymphocytes in Peyer's patches of mice after total lymphoid irradiation.

The depletion and repopulation of lymphocytes in specific cellular domains of mouse Peyer's patches were examined following total lymphoid irradiation (TLI). BALB/c mice 5-months-old were given 17 fractionated doses of irradiation to a total of 3400 to 4250 rads over a 4-week period, and Peyer's patches were examined by immunohistochemistry at 1 to 4 days and 1 to 4 weeks after TLI. Cryostat sections were labeled with monoclonal antibodies directed against B220 (B cells), Thy-1.2 (all T cells), L3T4 (helper T cells), and Ly-2 (cytotoxic/suppressor T cells). In depleted mice, Peyer's patches were greatly reduced in size in comparison to controls, although the structural framework of follicles, domes, and interfollicular areas was still present. B cells in follicles were reduced to a small core of B220+ cells interspersed with nonlymphocytic cells. T cells were virtually eliminated from the patch except for a small population of Thy-1.2+ cells that were neither L3T4+ nor Ly-2+ in follicle domes. During early stages of repopulation at 1 to 2 weeks after TLI, follicles increased in size and were populated by helper T cells but Peyer's patches lacked discrete interfollicular T cell regions. At 3 to 4 weeks after TLI, T cell regions were found in interfollicular areas. The results indicate that morphologically distinct cellular domains are maintained in Peyer's patches after TLI which are sequentially repopulated by immigrating lymphocytes.