Short-term consumption of n-3 PUFAs increases murine IL-5 levels but IL-5 is not the mechanistic link between n-3 fatty acids and changes in B cell populations

摘要

N-3 polyunsaturated fatty acids (PUFA) exert immunomodulatory effects on B cells. We previously demonstrated that n-3 PUFAs enhanced the relative percentage and/or frequency of select B2 cell subsets. The objectives here were to determine if n-3 PUFAs: i) could boost cytokines that target B cell frequency, ii) enhance the frequency of the B1 population and iii) to identify the mechanism by which n-3 PUFAs modify the proportion of B cells. Administration of n-3 PUFAs as fish oil to C57BL/6 mice enhanced secretion of the Th2 cytokine IL-5 but not IL-9 or IL-13. N-3 PUFAs had no influence on the percentage or frequency of peritoneal B1 or B2 cells. Subsequent experiments with IL-5^−/− knockout mice showed n-3 PUFAs decreased the percentage of bone marrow B220^loIgM^hi cells and increased the proportion and number of splenic IgM⁺IgD^loCD21^lo cells compared to the control. These results, when compared with our previous findings with wild type mice, suggested IL-5 had no role in mediating the effect of n-3 PUFAs on B cell populations. To confirm this conclusion, we assayed IL-5 secretion in a diet-induced obesity model in which n-3 PUFAs enhanced the frequency of select B cell subsets. N-3 PUFA supplementation as ethyl esters to obesogenic diets did not alter circulating IL-5 levels. Altogether, the data establish that n-3 PUFAs as fish oil can increase circulating IL-5 in lean mice, which has implications for several disease endpoints, but this increase in IL-5 is not the mechanistic link between n-3 PUFAs and changes in B cell populations.