A study to assess inducible nitric oxide synthase expression in oral lichen planus

Nitric oxide (NO) has been implicated in a variety of diseases but has not been previously studied in oral lichen planus (OLP). Since OLP has a comple x immunogenesis with abundant macrophage infiltration, this study determine d by immunohistochemistry whether or not the expression of the inducible fo rm of nitric oxide synthase (iNOS) was increased in this condition relative to normal mucosa. Thirty cases of OLP and 10 normal buccal mucosa biopsies were studied utilising primary antibodies to iNOS and CD68, a myelomonocyt ic marker. iNOS activity was additionally assessed using a [(14)-C]-labelle d arginine to citrulline assay. CD68 expression was significantly increased in the cellular infiltrate of all 30 cases of OLP compared with normal muc osa (P<0.009). Although iNOS staining was seen in a minority of cells in ni ne cases, this was not statistically significant when compared with the abs ent staining in normal oral mucosa (P=0.26). Furthermore, the minimal iNOS activity found in OLP was similar to that in normal mucosa. We conclude tha t expression of iNOS by macrophages is downregulated in OLP and discuss the possible reasons for this finding.