Correction of a murine mammary tumor virus-associated immunological depression by selective immunosuppression with cytosine arabinoside.

Mammary tumor virus (MTV) infection has been shown to be associated with a diminished hypersensitive reaction to methylated bovine serum albumin. Since methylated bovine serum albumin-induced hypersensitivity appears to be a mixed [humoral versus cell-mediated immunity (CMI)] reaction, the deficit in reactivity could be caused by, among other things, a direct depression of CMI or an increase in a humoral, blocking component. Assay of oxazolone-induced contact sensitivity and phytohemagglutinin-induced lymphocyte stimulation revealed normal or greater than normal CMI in MTV-positive animals. Treatment of MTV-positive and -negative animals with a regimen of cytosine arabinoside designed to inhibit only humoral immunity and leave CMI intact, corrected the deficit in methylated bovine serum albumin reactivity in MTV-positive mice. Thus, it is suggested that MTV infection may facilitate the production of interfering or blocking humoral immunity.