Abstract

While rheumatoid-factor-producing haemolytic plaque-forming cells (RF--PFC) of the human peripheral blood were easily inhibited by cycloheximide, mouse spleen cells immune to sheep red cells (anti-SRC PFC) were inhibited only after prolonged preincubation in the drug. The RF--PFC were easily inhibited by propranolol, while the anti-SRC PFC were not at all inhibited. Vinblastine inhibited both systems equally. These differences are taken to suggest that the RF--PFC have very little preformed antibody in them and therefore depend upon active protein synthesis for their demonstration. In contrast, anti-SRC PFC, which may be predominantly mature plasma cells, generally need no new protein synthesis for their demonstration because of increased quantities of preformed antibody. A possible mechanism is that RF--PFC may represent primarily RF-specific B cells, the RF of which is released by surface immunoglobulin shedding and therefore susceptible to membrane stabilising agents such as propranolol.