Dietary fish oil increases the proportion of a specific neutrophil subpopulation in blood and total neutrophils in peritoneum of mice following endotoxin-induced inflammation.

Omega-3 polyunsaturated fatty acids may have beneficial effects in inflammation, where neutrophil migration and activation are of importance. The effects of dietary fish oil on neutrophil numbers and subpopulations in healthy mice and mice with endotoxin-induced inflammation were determined. Mice were fed a control diet with or without 2.8% fish oil, and half of them were injected intraperitoneally with endotoxin. Blood, peritoneal lavage, bone marrow and spleen were collected. Expression of cell surface molecules was analyzed by flow cytometry, and chemokine concentrations were determined by enzyme-linked immunosorbent assay. Dietary fish oil did not alter the proportion of total neutrophils in blood but increased the proportion of a specific subpopulation of neutrophils 48 h following endotoxin administration. This subpopulation of neutrophils expressed higher levels of CD11b, Ly6G and major histocompatibility complex-II, suggesting a different role for these neutrophils in the inflammatory response. Dietary fish oil did not affect neutrophil numbers in the peritoneum of healthy mice, but 12 h after endotoxin administration, there were fewer neutrophils in the peritoneum of mice fed the fish oil diet than in mice fed the control diet. However, 48 h after endotoxin administration, mice fed the fish oil diet had more neutrophils in peritoneum than mice fed the control diet. These results indicate that, although dietary fish oil may delay recruitment of neutrophils from blood to the peritoneum early in inflammation, it has the potential to increase the number of peritoneal neutrophils later, which may be of benefit as impaired neutrophil migration and activation have been associated with immunosuppression late in inflammation.