Linoleic acid enhances mitogen response and survival of septic weanling rats

Abstract

Immunologic responses to various dietary fats and concentrations remain controversial. The authors examined the effect of dietary omega-3 and omega-6 polyunsaturated fatty acids (PUFA) on the immune system of weanling rats. Male weanling Sprague-Dawley rats were fed special liquid diets based on a standard enteral formula: (I) control: 2.2% calories as safflower oil (linoleic acid), (II) omega-3: 2.2% calories as safflower oil and 30% calories as cod liver oil (linolenic acid), and (III) omega-6: 32.2% calories as safflower oil. Body weight and caloric intake were measured daily. Rats were fed special diets for 18 days, at which time they were subjected to either septic challenge with 2 × 10 3 colony forming units of Streptococcus pneumoniae (eight rats per diet group) or killed and a splenocyte mitogen assay performed (four rats per diet group). Supplementation with omega-6 resulted in prolonged survival after bacterial challenge (control, 30.5 ± 0.5 hours; omega-3, 31.6 ± 0.5; not significant; omega-6, 39.8 ± 5.0; P < .05). A significant difference in mitogenic stimulation was seen with omega-3 and omega-6 in response to PHA (control, 10,856 ± 3,342; omega-3, 14,605 ± 3,042; P < .05; omega-6, 35,737 ± 7,596; P < .05) and with omega-6 only in response to LPS (control, 3,543 ± 1,083; omega-3, 8,777 ± 1,269; omega-6, 10,101 ± 3,008). Previous studies have suggested that diets high in omega-6 PUFA are immunosuppressive because of an increase in the production of the dienoic prostaglandins. The data from the present study demonstrate that omega-6 PUFA increases septic survival time as well as enhances T- and B-cell response to mitogens in weanling rats. This may be the result of age-related differences in the way animals utilize nutrients.