Suppression of macrophage-mediated antibody-dependent killing of Schistosoma mansoni larvae by concanavalin A stimulated spleen cell-derived factor(s)

Culture supernatants (sup) from rat spleen cells stimulated with concanavalin A (Con A) sepharose 4B suppressed schistosomulum killing by macrophages in a system of antibody-dependent cell-mediated cytotoxicity (ADCC). (a) The suppressive effect of the sup was strongest when they were added to cultures at the start of the ADCC assay, and it was decreased when sup were added to cultures in which the ADCC assay had begun more than 3 h previously. (b) From the results of various experiments in ADCC reaction, it was suggested that the suppressive factor(s) inhibited at least in part the interaction between macrophages and antibodies which had been bound to schistosomula, and that the suppressive factor(s) was bound to the macrophage side. (c) The suppressive activity was partially inactivated by treatment at 56 degrees C for 30 min, and it was lost almost completely by the treatment at 100 degrees C for 10 min. (d) The suppressive factor(s) differed from known cytokines such as interleukin 1 (IL-1), interleukin 2 (IL-2), granulocyte-macrophage-colony stimulating factor (GM-CSF), interferon-gamma (IFN-gamma), and tumour necrosis factor (TNF).