Differentiated keratinocytes are responsible for TNF-alpha regulated production of macrophage inflammatory protein 3 alpha/CCL20, a potent chemokine for Langerhans cells

The recruitment of immature dendritic cells into the epidermis is a key ste p in the development of cutaneous immunity, although the mechanism remains to be clarified. Recently, it was reported that both macrophage inflammator y protein 3 alpha (MIP-3 alpha)/CCL20 produced by keratinocytes and TNF-a a re important in recruiting Langerhans cells (LC) to the epidermis. In this study, we examined the production of MIP-3a by human keratinocytes stimulat ed with TNF-alpha. Cultured keratinocytes showed enhanced expression of MIP -3 alpha mRNA and protein when stimulated with TNF-a. In addition, conditio ned medium from TNF-a-stimulated keratinocyte cultures induced the migratio n of L1.2 cells expressing CCR6. We next examined the production of MIP-3a in stratified keratinocytes and found that, in contrast to non-stratified k eratinocytes, stimulation with TNF-a increased the expression of MIP-3a mRN A and protein. Moreover, skin samples grown in organ culture and treated wi th TNF-a showed MIP-3a in the keratinocytes of the spinous layer, but not i n the basal layer, by immunofluorescence staining. Based on these results, we postulate that MIP-3a produced by keratinocytes in the spinous layer in response to TNF-a stimulation is a key chemokine responsible for the epider mal recruitment of Langerhans cells. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.