Effects of Obesity-Associated Chronic Inflammation on Peripheral Blood Immunophenotype Are Not Mediated by TNF in Female C57BL/6J Mice

Chronic low-grade systemic inflammation in obesity contributes to the development and progression of aspects of metabolic syndrome. In obese male mice, expanded adipose tissue releases proinflammatory cytokines, including TNF, which promotes an increase in immature, proinflammatory, peripheral blood Ly-6C^high monocytes. The aim of this study was to characterize how TNF alters circulating cellular immunity in female mice with diet-induced obesity. We initially quantified peripheral blood immune cells by flow cytometry in female wild-type C57BL/6J mice after 3-30 wk of allocation to a high-fat (HF) or standard chow diet. We assessed effects of diet and time on neutrophil, monocyte, B cell, NK cell, CD4⁺ T cell, and CD8⁺ T cell populations. There was a significant interaction of the effects of diet type and time on the numbers and prevalence of circulating total monocytes and Ly-6C^high, Ly-6C^low, and Ly-6C^- subsets. Circulating monocytes, in particular Ly-6C^high monocytes, were increased in HF-fed mice compared with chow-fed mice. Ly-6C^high monocytes from HF-fed mice also had a more immature phenotype yet were highly responsive to the chemotactic ligand CCL2 and had greater intracellular production of TNF. Comparisons of the effects of HF diet feeding in littermate wild-type (TNF^+/+) and TNF^-/- female mice showed that genetic ablation of TNF did not protect from higher adiposity or an increase in circulating, immature, proinflammatory Ly-6C^high monocytes during HF diet-induced obesity. These data emphasize the importance of considering biological sex when determining the mechanisms of TNF action in obesity-induced cellular inflammation and in other chronic inflammatory conditions.