Immunosuppression during viral oncogenesis. V. Resistance to virus-induced immunosuppressive factor

Rabbits given malignant rabbit fibroma virus (MV) develop severe immunologic dysfunction during the course of infection. Splenic T lymphocytes from these rabbits elaborate a soluble non-specific immunosuppressive factor (virus-induced suppressor factor (VISF]. As malignant rabbit fibroma virus infection progresses, normal immunologic responsiveness returns. This recovery is multi-factorial and involves production by T lymphocytes of a soluble factor capable of antagonizing the activity of VISF. This soluble anti-suppressor factor (ASF) is not a generalized immunologic potentiator. Its sole apparent effect on immune function appears to be to antagonize the activity of VISF. The protective effects of ASF are evident only when suppressor factors and ASF are simultaneously present in culture. Pre-treatment of target cells with ASF-containing culture supernatants does not render them insensitive to the immunosuppressive effects of subsequent treatment with VISF. In addition, ASF appears to be directly responsible for antagonizing VISF activity. That is, ASF does not appear to initiate an anti-suppressive cascade by activating a population of cells that in turn generate secondary protective factors. ASF-producing cells do not bind Vicia villosa lectin, as do contra-suppressor cells described by others. In almost all of these features, the system we describe herein differs from systems in which other investigators have described factors that antagonize the effects of suppressor factors.