Inhibition of in vitro immune response by factor(s) prepared from lymphoid cells of old animals

It has been shown previously that cells from long-term calf lymphoid cell cultures (8--9 months) contain factors able to inhibit in vitro immune response. We report here that extracts prepared from lymph node cells freshly removed from old cows also contain similar factors inhibiting primary and secondary in vitro responses of mouse spleen cells against sheep red blood cells. These extracts do not affect cell viability nor stimulation with B or T mitogen (LPS or Con A). They do not affect production of antibodies by previously differentiated cells such as plasmocytomes or hybridomes. The active factor(s) appear(s) to behave as protein(s) of molecular weight about 10 000. Our results suggest that analogous "ageing" events occur either in long-term cultures of lymphocytes or in lymphoid cells of senescent animals. These phenomena would involve production or activation of specific factor(s) capable of inhibiting antibody synthesis by intervening at the level of differentiation of lymphocytes stimulated either by T-dependent or T-independent antigens.