Biology and function of adipose tissue macrophages, dendritic cells and B cells

The increasing incidence of obesity and its socio-economical impact is a global health issue due to its associated co-morbidities, namely diabetes and cardiovascular disease [ 1 Flegal K.M. Ogden C.L. Use of projection analyses and obesity trends-reply. J. Am. Med. Assoc. 2016; 316: 1317 Crossref Scopus (0) Google Scholar , 2 Ng M. Fleming T. Robinson M. et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2014; 384: 766-781 Abstract Full Text Full Text PDF PubMed Scopus (5258) Google Scholar , 3 Withrow D. Alter D.A. The economic burden of obesity worldwide: a systematic review of the direct costs of obesity. Obes. Rev. 2011; 12: 131-141 Crossref PubMed Scopus (451) Google Scholar , 4 Tsai A.G. Williamson D.F. Glick H.A. Direct medical cost of overweight and obesity in the USA: a quantitative systematic review. Obes. Rev. 2011; 12: 50-61 Crossref PubMed Scopus (213) Google Scholar , 5 Wang Y.C. McPherson K. Marsh T. et al. Health and economic burden of the projected obesity trends in the USA and the UK. Lancet. 2011; 378: 815-825 Abstract Full Text Full Text PDF PubMed Scopus (1415) Google Scholar ]. Obesity is characterized by an increase in adipose tissue, which promotes the recruitment of immune cells resulting in low-grade inflammation and dysfunctional metabolism. Macrophages are the most abundant immune cells in the adipose tissue of mice and humans. The adipose tissue also contains other myeloid cells (dendritic cells (DC) and neutrophils) and to a lesser extent lymphocyte populations, including T cells, B cells, Natural Killer (NK) and Natural Killer T (NKT) cells. While the majority of studies have linked adipose tissue macrophages (ATM) to the development of low-grade inflammation and co-morbidities associated with obesity, emerging evidence suggests for a role of other immune cells within the adipose tissue that may act in part by supporting macrophage homeostasis. In this review, we summarize the current knowledge of the functions ATMs, DCs and B cells possess during steady-state and obesity.