Immune recognition of cytochrome c II. — The role of macrophages as modulators and not as antigen-presenting cells in immune response in vitro

C57BL mouse peritoneal macrophages sensitized with cytochrome c (cyt. c) in complete Freund adjuvant (CFA) in vivo were able to capture, internalize and reexpress horse cyt.c on their surface. The major portion of cyt.c captured came out of macrophages in 1 to 3 h, with molecular weight unmodified. Cyt.c could be partly cleaved into two fragments, with molecular masses of about 2-2.5 and 10 kD by external non-serine proteases. The dynamics of macrophage interactions with cyt.c coupled to fluorescent latex beads was also studied. Macrophages were shown not to present cyt.c in the immune response in vitro, but rather to modulate the response level. The activating substance was secreted into the culture fluid, while suppressive activity was mediated by the cells.