Membrane lipid modification and immune function

Variation in the dietary intake of specific nutrients is known to influence the immune response, but only relatively recently has much attention been paid to the role of dietary fat.In 1976 Mertin & Hunt reported that essential fatty acid deficiency could significantly accelerate the rejection of skin allografts in mice, a response closely associated with cell-mediated immunity.In the same year it was reported that susceptibility to infection with coxsackie virus B was enhanced in hypercholesterolaemic mice (Loria et al. 1976) and, later, that normal plasma lipoproteins could inhibit lymphocyte proliferation in response to lectins or allogeneic cells (Morse et al. 1977).At about this time also, there was renewed interest in the mechanisms underlying the association between certain forms of cancer and dietary fat, which had emerged both from epidemiological and animal studies (Carroll & Khor, 1975).A number of reports indicated that the increased tumorigenesis associated with high levels of dietary fat could result from a modified immune response (Broitman et al.I 977; Santiago-Delpin & Szepsenwol, 1977;Kollmorgen et al. 1979).Since then, a considerable interest has arisen in the effect of lipids on the immune response.However, there has been some disagreement between laboratories on a number of points as described in the present review, and it is therefore necessary to emphasize at the outset that interpretation of the different results discussed requires precision in defining experimental indices.For example, it is necessary to segregate results obtained from experiments in which fatty acids are administered by subcutaneous injection from those derived from dietary treatment.It is even apparent that administration of acids by mouth may not be equivalent in effect to dietary supplementation (Sanders et al. 1985).Moreover, if a fat-free diet is compared with a diet rich in polyunsaturated fatty acids it is unclear whether it is the difference in quantity or the quality of the fat that is responsible for any difference between treated groups.It is equally important to define the assay used.Both delayed-type hypersensitivity responses and tests for cytotoxicity represent phenomena associated with the cell-mediated immune response, but the point at which the mechanisms are affected by dietary lipid may differ.Even in evaluating a single type of response, the experimental conditions of two different types of assay may be such that the lipid may influence the outcome differently in the two different assays.