CX(3)CL1 (fractalkine) and its receptor CX(3)CR1 regulate atopic dermatitis by controlling effector T cell retention in inflamed skin

Atopic dermatitis (AD) is a chronic allergic dermatosis characterized by epidermal thickening and dermal inflammatory infiltrates with a dominant Th2 profile during the acute phase, whereas a Th1 profile is characteristic of the chronic stage. Among chemokines and chemokine receptors associated with inflammation, increased levels of CX(3)CL1 (fractalkine) and its unique receptor, CX(3)CR1, have been observed in human AD. We have thus investigated their role and mechanism of action in experimental models of AD and psoriasis. AD pathology and immune responses, but not psoriasis, were profoundly decreased in CX(3)CR1-deficient mice and upon blocking CX(3)CL1–CX(3)CR1 interactions in wild-type mice. CX(3)CR1 deficiency affected neither antigen presentation nor T cell proliferation in vivo upon skin sensitization, but CX(3)CR1 expression by both Th2 and Th1 cells was required to induce AD. Surprisingly, unlike in allergic asthma, where CX(3)CL1 and CX(3)CR1 regulate the pathology by controlling effector CD4(+) T cell survival within inflamed tissues, adoptive transfer experiments established CX(3)CR1 as a key regulator of CD4(+) T cell retention in inflamed skin, indicating a new function for this chemokine receptor. Therefore, although CX(3)CR1 and CX(3)CL1 act through distinct mechanisms in different pathologies, our results further indicate their interest as promising therapeutic targets in allergic diseases.