The concentration of sterols in the plasma membrane of mouse lymphocytes will be manipulated. Lymphocytes with altered sterol composition may be obtained by (a) blocking off the synthesis of cholesterol de novo with some oxygenated derivatives of cholesterol, and (b) incubation of the cells with phospholipid "liposomes" which contain sterols in varying proportions and of different structures. The effect of this membrane manipulation on the performance of specific immunological functions of the lymphocytes will be studied. Parameters of lymphocyte functions to be examined are: target-cell killing by T-cells sensitized in vivo, cytotoxicity of T-cells sensitized in vitro, mixed lymphocyte reactions, antibody production by B-cells triggered in vivo and in vitro, antibody secretion by cultured myeloma cells, cap formation on Ig bearing cells, and leukocyte migration. We expect that a modification of the cholesterol component in the membrane of lymphocytes will influence (enhance or depress) these immunological functions. In addition, concanavalin A binding, endocytosis, and osmotic fragility of lymphocytes with altered sterol composition will be investigated.