Subcutaneous white adipose tissue: The deepest layer of the cutaneous immune barrier

Mammalian skin, the outer covering of the body, is composed of three layers, i.e. the epidermis, the dermis and the subcutaneous white adipose tissue (SWAT). While the contribution of epidermis and dermis to the skin's immune function is well established, the role, if any, of SWAT in this regard has yet to be determined. Human SWAT is made up of lobules which consist mainly of adipocytes and are subdivided and separated from each other by vascularized septae of connective tissue. An immunophenotypic analysis of liposuction-derived SWAT demonstrated that healthy subcutaneous fat tissue, although showing no overt signs of inflammation, harbors an indigenous system of immunocytes. As opposed to epidermis and dermis, they belong mainly to the mononuclear phagocyte lineage and, to a lesser extent, represent T-lymphocytes. Their phenotype indicates that these two major subsets of SWAT leukocytes are primarily concerned with ant-inflammatory and/or regulatory functions. It thus appears that SWAT is more than a cushion protecting against mechanical trauma, and may subserve immunomodulatory functions aimed at preventing or, at least, mitigating exaggerated immune and/or inflammatory reactions..