LANGERHANS CELLS EXPRESS INDUCIBLE NITRIC-OXIDE SYNTHASE AND PRODUCE NITRIC-OXIDE

The importance of nitric oxide (NO) in mediating macrophage functions has been demonstrated, but production of this potent gas has not been examined in Langerhans cells (LC). Using murine LC purified from epide rmal cell suspensions and the recently established LC-like cell line d erived from newborn BALB/c epidermis (XS-52), it was shown with revers e transcriptase (RT)-PCR that inducible nitric oxide synthase (iNOS) m essage is present in these cells. Murine keratinocytes did not contain iNOS message. iNOS mRNA was increased in a concentration-dependent ma nner by lipopolysaccharide (LPS) in purified murine LC and XS-52 cells , and immunofluorescence using an antibody to iNOS revealed bright cyt oplasmic staining in LPS-treated XS-52 cells, Anti-iNOS antibody brigh tly stained LC on human neonatal foreskin cryosections, An increase in NO production by LPS-treated XS-52 cells over 16 h, as measured by th e determination of nitrite levels in culture supernatants using the Gr iess Reaction, was observed. Interferon-gamma (IFN gamma) did not affe ct NO production on its own, In the presence of LPS and IFN gamma, NO production was 3 times more than observed with LPS alone. NO productio n was inhibited by the NOS inhibitor L-NAME. Western blots with anti-i NOS antibody demonstrated an increase in iNOS expression in LPS-treate d XS-52 cells that was suppressed by IL-10. NO produced in EC may affe ct LC functions such as microbicidal activity, antigen presentation, a nd cytotoxicity and may affect adjacent keratinocytes and melanocytes.