A subpopulation of T cells, mainly localized in the human skin, is activated by specific skin oils (lipids), such as free fatty acids and wax esters, according to a report published in Nature Immunology. Since skin disorders such as atopic dermatitis and psoriasis are associated with changes in skin lipids composition, these findings could provide candidate mechanisms by which alterations in lipid content might influence disease.
Sebum is a natural mixture of apolar skin lipids and waxy substances secreted through hair follicles or sweat glands that normally coats the skin surface. Annemieke De Jong and colleagues find that such apolar lipids, which are produced in large quantity by human sebaceous glands, activate CD1a-restricted T cells, while lipid antigens with polar heads are inhibitory to these T cells. Apolar lipids are largely restricted to the outer layers of the skin, while CD1a is highly expressed on antigen presenting cells in the epidermis. Trauma, infection or other breaches in skin barrier could transfer surface skin oils to deeper layers, promoting activation of CD1a-restricted T cells and barrier immunity.