Interleukin 5 regulation of peritoneal Ly-1 B lymphocyte proliferation, differentiation and autoantibody secretion.

The in vitro effects of recombinant interleukin (IL) 5 on proliferation and maturation of mouse Ly-1 B cells were studied. Most freshly isolated peritoneal Ly-1 B cells expressed high levels of IL5 receptor (R). Limiting dilution analyses showed that mitogens could reveal IL5 responsiveness in more than half of low density peritoneal Ly-1 B cells. IL 5 was able not only to increase the proportion of these Ly-1 B cells induced to proliferate, but it also shifted the clone size distribution of proliferating cells towards larger clone sizes. Splenic Ly-1 B cells also proliferated in response to mitogens plus IL5. Spontaneous and polyclonal activator-induced plaque-forming cell responses of Ly-1 B cells were increased by IL5. Furthermore, IL5 increased the frequency of peritoneal Ly-1 B cells induced to secrete certain autoantibodies. IL5 was certainly the agent responsible since its effects on both proliferation and differentiation were inhibited by either anti-IL5R monoclonal antibodies or by anti-IL5 monoclonal antibodies. Hence, Ly-1 B cells, IL5 and the IL5R appear to constitute a system of cellular proliferation, differentiation and some autoantibody production. Strategies specifically targeting the interleukin and receptor elements of this system might afford external control of these cellular responses.