The regulating effect of cholesterol derivatives isolated from human sera on lymphocyte response to phytohemagglutinin.

Cholesterol derivatives, including 7 alpha-hydroxycholesterol (7 alpha-HC), 7 beta-hydroxycholesterol (7 beta-HC), and 7-ketocholesterol (7-KC), were isolated from the Cohn fraction IV-I of normal human sera and were shown to be the moieties responsible for the suppression of lymphocyte proliferation. When 5-10 micrograms/ml of 7 alpha-HC, 7 beta-HC or 7-KC were added in vitro to lymphocyte cultures, incorporation of 3H-thymidine (3H-TdR) into the lymphocyte DNA was suppressed by about 50% when compared with the control. When 10-50 mg/kg/day of 7 alpha-HC, 7 beta-HC and 7 KC were administered in vivo to skin grafts on rats, the prolongation of skin grafts was observed. The concentration of 7-KC in cancer patient sera was 2 to 3 times the amount in normal pooled human sera.