Modulation of natural killer (nk) cell activity during FLV-P virus infection of mice.

We analyzed the effects of a polycythemic substrain of Friend leukemia virus, i.e. the FLV-P virus, on splenic NK activity of DBA/2 susceptible mice. One day after virus injection a significant increase of NK activity was found, which persisted until day 10. On the other hand, 14-21 days after virus injection a marked and significant depression of activity was measured. This depression was associated with the appearance of suppressor cells able to inhibit the lytic activity of untreated splenocytes when mixed in vitro in the 4 h 51Cr-release assay. The suppressor cell population was insensitive to treatment with anti-Thy 1.2 plus complement, was adherent to Sephadex G-10 and nylon, but did not adhere to plastic, suggesting it is neither a T-cell nor a typical macrophage. The possible relevance of NK activity modulation in relation to the induction of leukemia is discussed.