Effects of Dietary fatty acids on Neutrophil frequency and distribution

Abstract

Introduction: Obesity is an epidemic in our time and pre-disposes to lifestyle diseases which in its turn is associated with an increased susceptibility to infections. Polyunsaturated fatty acids have been shown to decrease mortality in experimentally induced sepsis in mice. Neutrophils are the first leukocytes recruited to inflammatory sites and important for defending the body against pathogens. Aims: In this study, the aim is to investigate the frequency of the neutrophils in the circulating pool (blood) and the frequency and distribution of neutrophils in the marginated pool which consists of bone marrow, spleen and liver. Methods: C57BL/6J mice were randomly assigned to Low-fat diet (LFD), High-fat diet, rich in saturated fatty acids (HFD-S) or High-fat diet, rich in polyunsaturated fatty acids (HFD-P). After eight weeks of dieting the mice were sacrificed and samples were collected for analysis. Blood was examined via an automated cellcounter. Samples of spleen and bone marrow were analyzed with flow cytometry for neutrophil markers and markers for egression and retention, respectively. Spleen and liver were examined by immunohistochemistry for neutrophils. Results: Mice fed HFD-P have increased frequency of neutrophils in both bone marrow and spleen compared to mice fed LFD and HFD-S. Neutrophils in bone marrow have decreased expression of CXCR4 (receptor for retention) in mice fed HFD-P compared to LFD, suggesting they are more easily recruited from the bone marrow. Hematologic analysis showed no increase in circulating neutrophils for mice fed HFD-P. Immunohistochemistry showed localization of neutrophils in the red pulp, predominantly in proximity of the marginal zone, but not in the white pulp. In liver the neutrophils are aligned close to the liver sinusoids. Conclusions: This study confirms that HFD-P increases the frequency of neutrophils in bone marrow and spleen. Further, HFD-P decreases the frequency of CXCR4, suggesting the neutrophils in those mice are more easily recruited to the circulation when needed, for example during infections.