The understanding of the role of adipose tissue has changed from a lipid storage organ to an endocrine and immunologically active organ. Here, we summarize the evidence for an important role of adipose tissue in innate immunity. The review focuses on the expression and function of Toll-like receptors (TLRs) in adipocytes and on the role of adipose tissue macrophages. The dual activation of TLR4 in adipocytes by lipopolysaccharide and fatty acids represents a molecular gate that connects innate immunity with metabolism. Dichotomic molecules derived from ancient precursor molecules control metabolism and immune function. Visceral adipose tissue is infiltrated by macrophages in obesity, and there is local crosstalk between these two types of cells, leading to an inflammatory transformation of adipose tissue.
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