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Immunological senescence. I. The role of suppressor cells.

The in vitro anti-SRBC response of several murine strains declined markedly with age in parallel with an increase in the activity of suppressor cells in the spleen and bone marrow which prevented early events during the induction of the immune response. These suppressor cells released soluble mediators and lacked the characteristics of mature T cells or macrophages. In addition the suppressor cell in the bone marrow could be removed on anti-Ig columns and fractions of old splenic suppressor cells sedimenting at 0.32 cm/h were greatly enriched in surface Ig bearing cells. Old immunodepressed mice did not lack potentially immunocompetent cells since the antibody response of old spleen cells could be restored by specifically activated T cells or lipopolysaccharide which act on B cells. These results suggest that a rise in the activity of non-T suppressor cells in the spleen and bone marrow may account, in part, for the depression in humoral immunity observed in aging mice.