Non-specific regulatory mechanism of contact sensitivity: the requirement of intermediate cells for non-specific suppressor factor (NSF) activity.

Non-specific suppressor factor (NSF), which inhibits passive transfer of contact sensitivity (CS), is produced spontaneously from macrophage-like suppressor cells which were induced by intravenous (i.v.) administration of oxazolone (Ox)-conjugated spleen cells. NSF is absorbed with normal spleen cells, and NSF-treated spleen cells acquire the ability to suppress the transfer of the effector cell function of CS non-specifically. In the present study, the events involved in the suppression by NSF were investigated. The involvement of intermediate cells between NSF and effector T cells in the suppression by NSF was suggested by the following observations: (i) NSF was absorbed with plastic-adherent and cyclophosphamide (CY)-sensitive non-T cells present in normal spleen cells; (ii) deletion of plastic adherent and CY-sensitive cells but not of adult thymectomy (ATx)-sensitive cells from the effector cell population, rendered the effector cells resistant to the suppressor activity of NSF; (iii) reconstitution of CY-pretreated effector cell population with Thy-1-negative spleen cells restored the ability of NSF to suppress CY-pretreated effector cells function. On the contrary, reconstitution with Ia-negative spleen cells did not restore the ability of NSF to suppress CY-pretreated effector cells function. Thus, NSF may not suppress directly the effector T-cell function, but intermediate cells, which are possibly macrophage-like cells, may exert a suppressive role after absorbing NSF. Species specificity was observed between the interaction of NSF and intermediate cells. The possible role of the intermediate cells in the suppression circuit of CS by NSF is discussed.