Induction of the CD1a Langerhans cell marker on human monocytes

Monocytes have recently been recognized as a precursor of Langerhans cells. This study examined the regulatory influence of the epithelial environment on the putative first step of the transition towards a Langerhans cell phenotype—the induction of CD1a antigen. The keratinocyte-derived cytokines granulocyte-macrophage-colony-stimulating factor, tumour necrosis factor-α, interleukin-6, and interleukin-1β induced CD1a expression, as did supernatants of keratinocytes extracted from inflammatory sites (periodontitis). Induction was abrogated by transforming growth factor-β and a keratinocyte-derived interleukin-1 inhibitor. The optimal temperature for induction was 34°C, not 37°C. These results demonstrate that the components of the epithelial environment (cytokines and lower temperature) exert important influences, which may be part of local regulation of Langerhans cell development.