INTERLEUKIN-12 EXPRESSION IN HUMAN AFFERENT LYMPH DERIVED FROM THE INDUCTION-PHASE OF ALLERGIC CONTACT-DERMATITIS

Recent reports suggest that production of interleukin-12 (IL-12) by de ndritic cells and keratinocytes may play an important part in contact hypersensitivity reactions. In the present study we investigated mRNA and protein expression of IL-12 in human skin lymph derived from norma l untreated skin (n = 5) and from the induction phase of allergic cont act dermatitis (CD) (n = 5). mRNA levels were determined at various ti me points in the lymph cells by a nested reverse transcriptase-polymer ase chain reaction method. Time course analysis reproducibly revealed a constitutive expression of both IL-12 p40 and p35 mRNA in the migrat ing lymph cells in all volunteers. However no enhancement of the IL-12 mRNA signal was found during the induction phase of allergic CD. Furt hermore, as determined by a sensitive ELISA technique, IL-12 protein w as not detectable in 60 lymph samples derived from normal untreated sk in or in 68 lymph samples obtained during the induction phase of aller gic CD at any time point of the lymph cannulation. Ln conclusion, our findings indicate that no significant protein levels of IL-12 are wash ed out from the skin into the afferent lymph or are produced and relea sed by migrating lymph cells during the induction phase of allergic CD in vivo.