Constitutive expression of both subunits of interleukin-12 in human keratinocytes

Interleukin-12 (IL-12), a heterodimeric molecule consisting of disulfide-linked 35- and 40-kDa chains, is secreted by a variety of cells including macrophages and B cells. While keratinocytes have recently been demonstrated to produce IL-12 after stimulation with phorbol-12,13-dibutyrate as well as trinitrochlorobenzene, the constitutive expression of the two IL-12 subunits has remained controversial. In this study, we investigate if cultured keratinocytes derived from human epidermis and the follicle outer root sheath constitutively express IL-12. Total RNA was reverse transcribed to cDNA and amplified using a highly sensitive nested reverse transcriptase polymerase chain reaction. Both IL-12 p40 and p35 transcripts were detected in keratinocyte cultures. Moreover, low levels of the IL-12 p70 heterodimer were detected in the culture supernatants, as determined by a sensitive enzyme-linked immunosorbent assay. Since IL-12 is known to play an important role in the development of Th1 cells, the constitutive expression of mRNA for IL-12 in keratinocytes together with its secretion adds further evidence for a role of keratinocytes in immunological processes within the skin such as in contact hypersensitivity.