Conversion of immune response patterns from high to low and low to high by an RNase-sensitive thymocyte extract

In vitro immune responses to human serum albumin (HSA) and synthetic polypeptides (T,G)-A-L, and (H,G)-A-L, associated with the maturation IgG-forming plasma cells were studied in relation to thymic low molecular weight RNA. This RNA, from normal low-responder animals to these antigens, converted high-responder bone marrow cells to low responders, whereas RNA from high responders converted low-responder bone marrow cells to high responders. These changes of immune response patterns were observed not only in the combination of allogeneic mouse cells and RNA, but also in xenogeneic rat and mouse systems. Thymic RNA from low-responder animals had no suppressive activity to high-responder RNA, when both were added together to one dish with antigen. High doses (x 50) of low-responder thymic RNA stimulated the same immune response level as a regular amount of high-responder thymic RNA. Intact thymocytes derived from low-responder mice added together with high-responder thymic RNA did not suppress immune response of high-responder bone marrow cultures. Intact allogeneic thymocytes also induced the same response as allogeneic thymic RNA. These results indicate that humoral immune responses can be influenced by thymic RNA derived from normal animals.