Changes in adipose tissue macrophages and T cells during aging

• Published in: Critical reviews in immunology Vol. 34; no. 1; pp. 1 - 14
• Main Authors: Garg, Sanjay K, Delaney, Colin, Shi, Hang, Yung, Raymond
• Format: Journal Article
• Language: English
• Published: United States 2014
• Subjects: Adipose Tissue - immunology; Aging - immunology; Animals; Cytokines - metabolism; Humans; Inflammation Mediators - metabolism; Macrophages - immunology; Mice; Obesity - immunology; T-Lymphocytes - immunology
• ISSN: 1040-8401; 2162-6472
• DOI: 10.1615/CritRevImmunol.2013006833

Adipose tissue historically was believed to be an inert tissue, functioning primarily in the storage of energy and thermal homeostasis. However, recent discoveries point toward a critical role for adipocytes in endocrine function as well as immune regulation. Excess body fat, accumulated through aging and/or a calorie-rich diet, is associated with many chronic metabolic and inflammatory diseases. Within the stromal vascular fraction of adipose tissue, macrophages and T cells accumulate with increasing tissue mass, secreting pro- or anti-inflammatory cytokines. In this review we discuss the current understanding of immune cell function in both diet-induced and age-related obesity. In both models of obesity, the classically activated, pro-inflammatory (M1) subtype takes precedence over the alternatively activated, anti-inflammatory (M2) macrophages, causing tissue necrosis and releasing pro-inflammatory cytokines like interleukin-6. Other distinct adipose tissue macrophage subtypes have been identified by surface marker expression and their functions characterized. Adipose tissue T cell recruitment to adipose tissue is also different between aging- and diet-induced obesity. Under both conditions, T cells exhibit restricted T-cell receptor diversity and produce higher levels of pro-inflammatory signals like interferon-γ and granzyme B relative to young or healthy mice. However, numbers of regulatory T cells are dramatically different between the 2 models of obesity. Taken together, these findings suggest models of age- and diet-induced obesity may be more distinct than previously thought, with many questions yet to be resolved in this multidimensional disease.