The immunoregulatory role of cholesterol and other lipids: a hypothesis.

Membrane lipids play an important role in cellular responses to exogenous signals. In immunocompetent lymphocytes, marked changes in the concentrations of membrane lipids occur following cell-antigen interaction. These changes lead to an increase in membrane fluidity, thus facilitating the microaggregation of receptor-antigen complexes. This event constitutes the inductive signal for lymphocytes. Lipid profile alterations leading to increased concentration of membrane cholesterol, of polyunsaturated lipids, or of both, bring about a decrease in membrane fluidity. The latter interferes with receptor displacement preventing delivery of an inductive signal to the responding cell. Interference with microaggregation is readily brought about in interactions involving low affinity antigens, such as tumoral antigens. We postulate that in hyperlipidemic and hypercholesterolemic states there is decreased immune responsiveness to weak antigens due to the aformentioned lipid profile alterations in the membranes of immunocompetent cells. The manner in which an increase in the concentration of the lipids mentioned can lead to decreased immune responsiveness and hence to an increased incidence of malignancies in hyperlipidemic and hypercholesterolemic states is the hypothesis presented in this paper.