Systemic and in situ natural killer and suppressor cell activities in mice bearing progressively growing murine sarcoma-virus-induced tumors.

The activity of systemic and in situ natural killer (NK) cells was measured in 3- to 5-week-old CBA mice with progressively growing murine sarcoma virus (MSV)-induced tumors. Splenic NK activity was depressed in tumor-bearing mice. NK activity was quite low or not detectable in unfractionated cell suspensions from the tumors 10-12 days after inoculation of virus, but activity was observed upon depletion of phagocytic and/or adherent cells. To determine whether this in situ inhibition of NK activity was correlated with the presence of previously described suppressor cells, subpopulations of cells from the tumors were tested for their ability to suppress various responses of normal spleen cells: NK activity, lymphoproliferative responses to concanavalin A, and proliferation-independent production of macrophage inhibition factor. A similar pattern of suppressor activity was seen in all of the assays, indicating the presence of pleiotropic suppressor cells in progressively growing MSV-induced tumors.