The immunoregulatory role of cholesterol and other lipids: a hypothesis

Leishmania donovani Affects Antigen Presentation of Macrophage by Disrupting Lipid Rafts

Leishmania donovani-infected splenic macrophages and P388D1 (P388D1(I)) failed to activate T cells in response to low dose of exogenous peptide. The membrane fluidity of P388D1(I) was greater than that of the normal counterpart P388D1(N), but could be reduced either by exposing the cell below phase transition point or by loading cholesterol into membrane (L-P388D1(I)), and this was associated with enhanced Ag-presenting ability of P388D1(I). Presentation of endogenous leishmanial Ag, kinetoplastid membrane protein-11, was also defective, but could be corrected by loading cholesterol into membrane. Because membrane rafts are important for Ag presentation at a low peptide dose, raft architecture of P388D1(I) was studied using raft (CD48 and cholera toxin-B) and non-raft (CD71) markers in terms of their colocalization with I-A(d). Binding of anti-CD48 mAb and cholera toxin B subunit decreased significantly in P388D1(I), and consequently, colocalization with I-A(d) was not seen, but this could be restored in L-P388D1(I). Conversely, colocalization between I-A(d) and CD71 remained unaffected regardless of the presence or the absence of intracellular parasites. P388D1(N) and L-P388D1(I), but not P388D1(I), formed peptide-dependent synapse with T cells quite efficiently and this was found to be corroborated with both intracellular Ca2+ mobilization in T cells and IL-2 production. This indicated that intracellular parasites disrupt the membrane rafts, possibly by increasing the membrane fluidity, which could be corrected by making the membrane rigid. This may be a strategy that intracellular L. donovani adopts to evade host immune system.

Fatty acid unsaturation increases expression and capping of murine lymphocyte CD44 and CD45

We studied the effect of incubating murine lymphocytes with cis-unsaturated fatty acids on expression and capping of CD44 and CD45. Lymphocytes were incubated with stearic (18:0) or oleic (18:1 omega-9) acid bound to bovine serum albumin (BSA). After incubation with rat anti-CD44 or anti-CD45 monoclonal antibodies and then with fluorescent-labeled anti-rat antibody, mean fluorescence intensity (FI) was measured by using flow cytometry. Capping was measured after warning and fixation in paraformaldehyde. Steady-state fluorescence anisotropy (rs) was measured after the cells had been incubated with trimethylammoniumdiphenylhexatriene. Incubation with oleic acid, but not stearic acid or BSA alone, was associated with an increase in FI of CD44. Expression of CD45, however, was increased by both stearic and oleic acids to the same degree over BSA controls. CD44 and CD45 capping were both increased by incubation with oleic acid. Rs was decreased in cells incubated with oleic acid, suggesting an increase in membrane fluidity. We conclude that incubation with oleic acid increases expression of CD44 and increases capping of both CD44 and CD45. These findings were confirmed in feeding experiments, in which rs was reduced and CD44 capping increased by polyunsaturated fatty acid diets.

The effect of a high fat diet on the incidence of colonic cancer after cholecystectomy in mice

An experimental study was designed to evaluate the effects of both a high fat diet and a cholecystectomy on the incidence of carcinogen-induced colon cancer in mice. Sixty pink-eyed jax (P/J) mice were divided equally into two groups. One group was fed a standard rodent diet and the other group received a diet supplemented with 20% corn oil. From each diet group, 50% of the mice had a cholecystectomy and the other 50% had a sham operation. Two weeks after surgery, each mouse received weekly subcutaneous injections of a carcinogen (dimethylhydrazine, 20 mg/kg) for 12 weeks. After the treatment period, the mice were killed and their large bowels were examined. Evaluation of the results demonstrated that the mice that had a cholecystectomy and a high fat diet had the highest incidence (P less than 0.05) of colonic adenocarcinomas.

Inhibition of lymphocyte capping by fatty acids in mouse and man

Lipid-enriched diets have been related to a high cancer incidence in experimental animals for many years, and more recently, to assorted defects on the immune response. We investigated the effect of incubating human or murine (C3H/HEJ) lymphocytes with saturated (16:0) and unsaturated (18:1, 18:2, 18:3, 20:4) fatty acids (12 micrograms for each 10(7) cells), on the ability to cap with antihuman or antimouse anti-IgM, mu-chain specific antibody. Capping was also tested in obese (ob/ob, C57BL/6J) mice. Capping at 30 and 60 min was reduced by fatty acid incubation to 10-30% of control values in humans (p less than .001), and to 30% of control values in mice (p less than .01), regardless of degree of unsaturation. ob/ob capped normally. A lymphocyte membrane effect caused by fatty acids is observed in these experiments. Whether this is related to the dysimmunity caused by lipid diets cannot be assessed from our data, especially since all fatty acids, regardless of unsaturation, reduced the capping phenomenon.

Myotonic dystrophy: a disease caused by functional zinc deficiency due to an abnormal zinc-binding ligand?

There are large amounts of zinc in muscle and zinc ions can enhance the degree of muscle contraction in response to direct stimulation while at the same time inhibiting neuromuscular transmission. The opposites of these effects would lead to myotonia and muscle weakness. There are many parallels between the non-muscular features of myotonic dystrophy and those of zinc deficiency. The particular patterns of reproductive disturbance in both males and females, the abnormalities of metabolism, the defects in gut funcion, the defects in bone and the congenital abnormalities are very similar in the two conditions. However there are important differences between simply zinc deficiency states and myotonic dystrophy which mean that the latter is unlikely to be due to the former. Instead it is proposed that the fundamental defect in myotonic dystrophy is the presence of an abnormal zinc binding ligand which fails to deliver appropriate amounts of zinc ions to the tissues. The functioning of this ligand may, however, be affected by dietary zinc, perhaps accounting for the apparent variation in the expression of the dominant myotonic dystrophy gene due to some unknown environmental factor. Some of the effects of zinc may be due to lack of the zinc ion directly, while others are probably related to defects in essential fatty acid and prostaglandin metabolism. The hypothesis can be readily tested by the employment of nutritional measures designed to counteract the defects in zinc and essential fatty acid metabolism.