Immunosuppressive actions of retroviruses.

The immunosuppressive properties of retroviruses were first demonstrated by Old et al. We later showed that Gross Passage A retrovirus superinfection in mice resulted in decreased antibody production and diminished allograft rejection. We have studied in some detail the immunosuppression which occurs subsequent to infection with feline leukemia virus (FeLV) as characterized by profoundly depressed T and B lymphocyte responses and decreased production of gamma-interferon. Injection of staphylococcal protein A (SPA) corrected these deficient immune responses, cleared circulating FeLV from blood and produced a regression of FeLV-induced lymphomas and leukemias. The immunosuppressive properties of FeLV and certain other retroviruses have been linked to the transmembrane viral envelope peptide, p15E. Cianciolo et al synthesized a 17-amino acid viral component which shares sequence homology with a highly conserved region of p15E. In vitro analyses have shown that this synthetic retroviral peptide suppresses T and B cell functions, inhibits the generation of cytotoxic lymphocyte (CTL) responses and dramatically alters the morphology and distribution of monocytes. The latter finding, along with reports that cells of the monocyte/macrophage lineage play a critical role in the initiation of human immunodeficiency infection, suggests that monocytes and macrophages may play a crucial role in retroviral infection and some of the associated immunodeficiencies associated with retroviral infection.