IL-12 IS EXPRESSED AND RELEASED BY HUMAN KERATINOCYTES AND EPIDERMOIDCARCINOMA CELL-LINES

IL-12 is a 70-kDa heterodimeric cytokine composed of two covalently li nked chains, p40 and p35. IL-12 has multiple effects on T and NK cells and recently was found to be required for optimal Th1 cell developmen t. In a variety of inflammatory skin disorders including delayed type hypersensitivity and contact hypersensitivity, Th1 cells appear to be critically involved. Because keratinocytes are well known to exhibit t he capacity to release a variety of proinflammatory and immunologic cy tokines, and thereby to be able to modulate inflammatory and immune re actions within the skin, it was investigated whether human keratinocyt es and keratinocyte cell lines can release IL-12. Supernatants of phor bol-12,13-dibutyrate (PDBu) stimulated human epidermoid carcinoma cell lines (KB, A431) induced IFN-gamma production by PBL. This activity c ould be completely blocked by the addition of an anti-IL-12 Ab directe d against the p40 subunit of IL-12 (C8.6). Release of IL-12 by keratin ocyte cell lines was further confirmed by an RIA specific for p40. Imm unoprecipitation under reducing conditions using the C8.6 Ab yielded s pecific bands at 40 kDa in supernatants of both KB cells and normal hu man keratinocytes. Northern blot analysis revealed IL-l 2-specific mRN A transcripts in PDBu-treated KB cells using cDNA probes encoding for p35 and p40. Moreover, by reverse transcription PCR specific transcrip ts for p35 and p40 were found in keratinocytes. These data indicate th at keratinocyte cell lines and, although to a much lesser degree, norm al human keratinocytes, exhibit the capacity to make IL-12; thus demon strating for the first time IL-12 production by nonhemopoietic cells. Thus, one may speculate that keratinocytes via this capacity may influ ence the fate of Th-mediated immune responses, favoring Th1 responses by enhanced production of IL-12 or Th2 responses by reduced IL-12 rele ase.