There have been several reports of the effects of various fatty acids upon mitogen-stimulated lymphocyte proliferation. One approach has been to add the fatty acids directly to phytohaemagglutinin (PHA)-stimulated lymphocytes growing in culture I 1-51, These studies have all shown a reduced response to PHA in the presence of fatty acid, although the extent of inhibition varied between studies, probably due to differences in protocol. A second approach has been t o measure mitogen-stimulated proliferation of lymphocytes obtained from animals fed diets rich in particular fatty acids. Results from such studies have been variable. For example, diets rich in linoleic acid, in comparison with those low in linolcic acid. either did not effect, increased or decreased proliferation (see 16 I for references). These studies have focused largely upon linolcic acid, owing to the finding that plasma linoleic acid levels are lowered in multiple sclerosis. possibly leading to removal of an immunosuppressive cffect of the acid. In recent timcs, however, it has been suggested that the polyunsaturated fatty acids, especially those of fish oil origin, may have immunosuppressive properties 17. 81 and may be useful in treatment of autoimmune diseases [ 91. Thcrcforc it was decided to investigate the effect of a wide range of fatty acids upon concanavalin A (Con A)-stimulated rat lymphocyte proliferation. Cervical lymph nodes were collected from male rats 1300 g), freed o f adipose tissue and gently ground. Lymphocytes were collected by centrifugation and washed twice. T h e cells wcrc cultured at 37°C in an air/CO, (19:l . by vol.) atmosphere at a density o f 5 x 10' cells/well in RPMI medium supplemented with 1 0 mM-glucose, 2 mM-ghtamine and l o ' % (v /v) fetal calf serum (dialysed for 48 h versus phosphate-buffered saline). T h e cell culture medium was also supplemented with Con A ( 5 pg/ml) and bovine serum albumin (BSA)-fatty acid complexes (0.1 mM o r 0.033 mMfatty acid; BSA/fatty acid ratio 1 : 1 ). T h e latter were prepared wing dcfattcd BSA. according to Mahoncy et (11. 1 I 0 I. Fatty acids uscd included saturated. monounsaturated and polyunsaturated fatty acids, including those of fish oi l origin. After 48 h /6-'H]thymidinc (0.2 pCi/wcll) was addcd t o each well and the cells incubated for a further 18 h. T h e cells wcrc harvested on to glass-fibre discs, which were washed and dried before measuremcnt o f radioactivity. Results (Fig. I ) are expressed as percentage o f the BSA alone (i.e. no additional fatty acid) I 'H I-thymidinc incorporation. Lymphocyte proliferation was inhibited by all fatty acids tested at both concentrations, except 14:O and 18:0, which were stimulatory at 0.033 mM. For all fatty acids, inhibition was greater at the higher concentration. At both concentrations, the grcatcst inhibition was found with 20:4. w 6 ; 20:5, cu3 and 18: 1, w9. Generally, saturated fatty acids were less inhibitory than unsaturated fatty acids, although, at 0 . 1 mM. stearic acid showed inhihition comparable with that o f thc unsaturated fatty acids. T h e two fish-oil-derived fatty acids tcsted showed greatly differing dcgrccs o f inhibition with 20:5, (n3 being morc cffcctive than 22:6, w3. These results confirm that a wide range o f fatty acids arc capable o f inhibiting lymphocyte proliferation i r r vitro. A s such it is clcar that fatty acids in general have an immunosuppressive effect, but that the effect is greatest if polyunsaturated
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