Lipoproteins suppress several immune functions (mitogen-induced lymphoblast transformation, macrophage functions). Low density lipoprotein (LDL) is responsible for most of these effects. Diet may cause an elevation in LDL level. Therefore, we investigated the effect of cholesterol-rich diet upon the mitogen response of rats. The cholesterol and LDL-cholesterol level of rats was elevated after 8 days of diet. The blastogenic response of spleen cells separated by Ficoll-Paque gradient decreased. The response to phytomitogens 1, and 10 micrograms/ml phytohaemagglutinin (PHA) and 10 micrograms/ml concanavalin A (Con A) was measured by thymidine incorporation after 3 days of culture. The decrease of blastogenic response was more pronounced at the higher doses (10 micrograms/ml PHA, and 10 micrograms/ml Con A). For the lymphocyte cultures that did not contain autologous (rat) serum, we suggest that suppressed response was caused by an alteration of either in the membrane or in the metabolism of cells participating in the mitogen response. The decreased amount of LDL receptors and a derangement in intracellular cholesterol biosynthesis are supposed. The clinical implications of the immunosuppressive effect of dietary cholesterol is discussed.
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