Inhibition of contact sensitivity by macrophages.

Lymphoid cells of mice injected with picrylsulphonic acid and then painted with picryl chloride produce a specific T suppressor factor (TSF) in vitro. This factor arms peritoneal exudate cells, which then produce a nonspecific factor which inhibits the transfer of contact sensitivity by immune cells incubated in it. An adherent, theta-negative cell, which is presumably a macrophage, is responsible. This justifies the use of the term macrophage suppressor factor. As a separate phenomenon, passive transfer cells lose their activity when incubated on high density monolayers of normal peritoneal exudate cells. However, this is not associated with the production of a supernatant factor. The inhibition of transfer when immune cells are incubated with specific TSF is unaffected by nylon wool filtration (which removes macrophages). This suggests that TSF is able to depress the passive transfer of contact sensitivity by a macrophage-independent process.