Skin-Resident Memory T Cells: Pathogenesis and Implication for the Treatment of Psoriasis.

Tissue-resident memory T cells (T) stay in the peripheral tissues for long periods of time, do not recirculate, and provide the first line of adaptive immune response in the residing tissues. Although T originate from circulating T cells, T are physiologically distinct from circulating T cells with the expression of tissue-residency markers, such as CD69 and CD103, and the characteristic profile of transcription factors. Besides defense against pathogens, the functional skew of skin T is indicated in chronic skin inflammatory diseases. In psoriasis, IL-17A-producing CD8 T are regarded as one of the pathogenic populations in skin. Although no licensed drugs that directly and specifically inhibit the activity of skin T are available to date, psoriatic skin T are affected in the current treatments of psoriasis. Targeting skin T or using T as a potential index for disease severity can be an attractive strategy in psoriasis.