The in vitro culture characteristics and requirements for expression of receptors for IgM on human peripheral blood lymphocytes.

The in vitro culture characteristics and requirements for expression of receptors for the Fc portion of IgM (Fcmu) on peripheral blood lymphocytes was investigated. Significant numbers of Fcmu receptors cells are not detected until after 11 hr of in vitro culture. This was demonstrated not to be the result of shedding in vivo bound IgM thus unblocking the Fcmu receptors after culturing but rather an increased number of Fcmu receptors on cultures cells, presumable because of de novo synthesis. It was also shown that the Fcmu and Fc gamma receptors are not mutually exclusive in that a small population of PBL exhibit both Fcmu and Fc gamma receptors and that Fcmu negative cells may become Fcmu positive cells. Furthermore, it was demonstrated that fetal bovine serum and human blood group AB serum which are known to affect differentially various in vitro cell mediated functions also differentially affect Fcmu receptor expression and are capable of modulating the Fcmu receptor levels. These observations demonstrate the diverse and dynamic nature of the Fcmu receptor.