In vivo modulation of thymus-derived lymphocytes with monoclonal antibodies in mice. II. Separation of natural killer cells and cytotoxic T cells.

Treatment of mice with ascitic fluid containing high titres of T24-31.7 monoclonal antibody (rat anti-mouse Thy-1) lead to a rapid loss of T cells from peripheral lymphoid organs. Spleen and lymph node tissue lost all detectable Thy-1+ and mitogen-responsive T cells within 72 hr. These tissues were completely T cell-depleted for more than a week before repopulation with T cells began. Lectin-induced splenic T cell cytoxicity in culture was lost within 72 hr after treatment of mice in vivo. In contrast, treatment of mice with T24-31.7 ascitic fluid was followed by an immediate increase in natural killer (NK) cell-mediated cytolytic activity. After 96 hr, NK activity began to decrease and did not reappear in the T cell-depleted spleens. While purified T24-31.7 antibody was responsible for T cell depletion in vivo, a non-immunoglobulin component of the ascitic fluid stimulated splenic NK cell activity. The presence of phytohaemagglutinin (PHA) on target cells in the lytic assay was shown to inhibit NK activity but enhance T cell-mediated cytotoxicity. The relationship of NK cells and cytotoxic T lymphocytes (CTL) to the T cell lineage is discussed.