Immunohistochemical observation of recovery of the periarteriolar lymphoid sheath, lymph follicle and marginal zone in the 60Co-irradiated spleen of rats.

After 60Co irradiation of rat spleen, the most severe damage was found initially in the lymph follicles (LFs); lymphocytes were decreased in number in the periarteriolar lymphoid sheath (PALS), and almost completely depleted in the marginal zone (MZ). Recovery was observed first in the PALS, followed by the LFs, and finally the MZ. From the results of immunohistochemistry, the process of recovery was assumed to involve migration of T and B lymphocytes along the arterioles from the area surrounding the terminal arteriole at the end of the PALS into the central part of the PALS and into the LF. Peripheral blood IgM+, IgD- B lymphocytes, known to be MZ precursor cells, flowed from the follicular artery to settle in the MZ. Furthermore, recovery of the PALS prior to the LFs was suggested to be essential for lymphocyte migration to the LFs.