Assay and characterization of an inhibitor of interferon action

Variations of interferon inactivators and/or inhibitors in human serum and their relationship to interferon therapy

Anti-interferon (IFN) activities of normal human sera and sera from cases suspected of viral infection were determined. Of the normal sera tested (57), 65% presented anti-IFN activities against IFN-alpha and/or -beta preparations; 61% against IFN-beta and 32% against IFN-alpha. Of the sera from suspected virus-infected individuals (44), 82% presented anti-IFN activity to IFN-beta and 57% to IFN-alpha with the majority of sera (91%) exerting anti-IFN activities to IFN-alpha and/or -beta preparation. The observed variations of anti-IFN alpha and beta activities of human sera appear to be reproducible and should be taken into consideration in the clinical application of IFN.

Two different pathways of interferon mediated suppression of antibody secretion

Interferon suppresses a variety of in vitro immune responses by a mechanism which has not been well defined. Both direct suppression and activation of suppressor T cells have been suggested as possible mechanisms of interferon action. In an attempt to examine this question interferon-alpha (IFN alpha)-mediated suppression of a plaque forming cell response to a T cell independent antigen by spleen cells or by B cells was examined. Somewhat greater quantities of IFN alpha were required to suppress plaque forming cell responses by B cells than by spleen cells to the antigen fluoresceinated-Brucella abortus (FITC-BA). However, suppression of spleen cell responses could be blocked by addition of either 2-mercaptoethanol, levamisole or monoclonal antibodies against the lymphokine, soluble immune response suppressor (SIRS), whereas suppression of B cell responses by interferon-alpha was unaffected by these agents. Each of these agents interferes with SIRS mediated suppression of immune responses. Addition of T cells to B cell cultures stimulated with FITC-BA did not affect the total plaque forming cell response nor the extent of suppression by IFN alpha, but it did restore 2-mercaptoethanol sensitivity to IFN alpha-mediated suppression. As few as 1 X 10(5) T cells were effective and it was necessary to add T cells within 3 h of addition of IFN alpha to confer 2-mercaptoethanol sensitivity to IFN alpha mediated suppression. These data suggest that IFN alpha can suppress immune responses by two different pathways and that in the presence of T cells, activation of suppressor T cells is the dominant pathway. The presence of T cells must also prevent direct suppression of B cells by IFN alpha.