B-cell-derived lymphokines: regulatory effects on the immune system.

While both regulatory and effector functions within the T cell lineage have been extensively studied, B lymphocytes have been considered merely a source of humoral antibodies until recently. With the exception of antibody feedback, only a limited number of investigations have been designed to explore the possibility that B cells may exert regulatory activity. The purpose of this review is to analyze how B cells can modulate themselves by generating signals (lymphokines), which under certain circumstances may initiate a chain of regulatory events. Only factors exclusively produced by B cells are considered. While, for the most part, this review is dedicated to recent studies on nonimmunoglobulin B cell factors, the role played by Ig molecules as immunoregulatory linker molecules, independently of their antigenic specificity, will be briefly examined. Furthermore, some basic questions regarding the biological significance of these regulatory mechanisms will be raised.