RADIATION-DAMAGE AND IMMUNE SUPPRESSION IN SPLENIC MONONUCLEAR CELL-POPULATIONS

We have examined alterations in all of the major splenic mononuclear c ell (SMNC) populations in C57B1/6 mice following whole-body irradiatio n (0-700 cGy) in order to determine which populations may play a role in active immune suppression and/or haematopoietic recovery. A protoco l has been established for characterization and differentiation by flo w cytometric analysis (FCA) of the major MNC populations in the mouse spleen: T lymphocytes (CD4(+) and CD8(+) cells), B lymphocytes, natura l killer (NK) cells, and monocytes/macrophages. Ionizing radiation cau sed decreased spleen cellularity and decreased ability of surviving SM NC to respond to mitogen. FCA revealed alterations in the relative com position of the constituent splenic cell populations following irradia tion, reflecting differential radiosensitivity, with selective enrichm ent of NK cells (seven-fold) and CD4(+) T lymphocytes (three-fold). En richment developed during the 7-day post-irradiation period. In additi on, some MNC became activated in a dose- and time-dependent fashion fo llowing whole-body irradiation, as indicated by expression of CD71, th e transferrin receptor. These cells were CD34(+) and Thy1.2(+), but we re CD4(-) or CD8(-) as well as CD45(-) (B cell). The observed increase in NK cells corresponds with a previously reported increase in natura l suppressor (NS) cells following total-lymphoid irradiation (TLI). Th e balance of recovery-inhibiting NK cells and recovery-enhancing CD4() T lymphocytes following irradiation may reflect or influence the deg ree of haematopoietic recovery, and may provide an indication of the e xtent of damage (biological dosimetry).