Interaction between 'sensitized lymphocytes' and antigen in vitro. 3. Release of soluble mediators by particulate antigen.

Guinea-pigs immunized with sheep red cells (SRC) in Freund's complete adjuvant (FCA) developed delayed type hypersensitivity to a SRC urea extract 7 days after sensitization and showed combined Arthus and delayed reactivity from the 14th day on. Animals immunized by an intracardiac injection of SRC in saline and skin tested 4–5 days later with SRC urea extract, responded with an erythematous and indurated lesion reaching its peak 24 hr after testing and resembling a typical delayed hypersensitivity reaction. Lymphocytes from lymph nodes, peritoneal exudate and peripheral blood of guinea-pigs immunized with SRC in FCA released skin reactive factor (SRF) and macrophage migration inhibitory factor (MIF) when cultured for 24 hr with SRC. No SRF was formed in the absence of divalent cations in the cultured medium. No SRF or MIF was produced by lymphocytes of guinea-pigs immunized by the intracardiac route and cultured under identical conditions. SRF obtained after exposure of sensitized lymphocytes to SRC was eluted from Sephadex G-200 in the region of serum albumin. Lytic anti-SRC antibody of the IgM class was liberated into the supernatant of spleen cultures, after intracardiac immunization and antibody of the IgG class was produced by lymph node cultures after immunization with SRC in FCA, in both cases in the absence of antigenic stimulation . It is considered improbable that the latter antibody is involved in the release of soluble mediators.