Host genotype influences immunomodulation by interferon.

Interferon influences both afferent and efferent pathways of delayed-type hypersensitivity (DH) in the mouse. In animals previously sensitised to picryl chloride, sheep red blood cells (SRBC) or Newcastle disease virus (NDV), and treated with interferon just before challenge with any of these antigens, the antigen-elicited reaction, as measured by the ear-swelling (picryl chloride) or footpad swelling (SRBC and NDV) test, is either decreased or completely inhibited, depending on the dose of interferon administered. In addition to this action on expression of the sensitised state, interferon decreases or inhibits sensitisation to SRBC or NDV when administered 24 h before immunisation. These effects were recently confirmed using electrophoretically pure mouse interferon, thus ruling out the possibility that they are caused by other proteins present in the previously used partially purified interferon preparations. For the effect on sensitisation, the timing of interferon administration is crucial, and when interferon is administered a few hours after the antigen, sensitisation can actually be enhanced, as reported here; the enhancement of sensitisation by interferon is influenced by the dose of antigen and by the genotype of the mice that are sensitised.