It has been known that peripheral blood lymphocytes are almost depleted soon after sublethal irradiation, and then are rapidly repopulated. The peripheral blood lymphocytes are composed of several subsets and their immunological functions are
different
among subsets. In this experiment, we tried to dissect the radiosensitivity of lymphocyte subsets using flow cytometry and to invastigate cell-mediated immune response of the reponse ofd the repopulated lymphocytes. After gamma irradiation of 500
rads,
the number of lymphocytes rapidly decreased, ind the order of CD8+, IgM+, Thy1.2+ and CD4+ cells, then rapidly repopulated, exceptd CD4+ T cells, by 3 weeks. Although CD4+ cells were less depleted than other lymphocyte subsets, the number of CD4+
T
cells was not completely recovered untill 7 weeks after irradiation, demonstrated that the ratio of CD4+ to CD8+ cells was reversed. Mixed lymphocyte reaction markedly decreased soon after irradiation, and remained low level by 7 weeks in which
the
total number of lymphocytes are almost repopulated.
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