Identification and induction of human keratinocyte-derived IL-12.

Abstract

Interleukin 12 is a heterodimeric molecule that serves as a potent co-stimulator enhancing the development of Thl cells. As one of the classical Thl cell-mediated responses is contact sensitivity in skin, we wondered whether IL-12 might be produced by epidermal cells and serve as a mediator of this immune response. Using a sensitive, quantitative PCR technique we demonstrate that p35 chain mRNA of IL-12 is produced constitutively by human epidermal cells, whereas p40 chain mRNA can only be detected in epidermis treated with contact allergen, but not epidermis exposed to irritants or tolerogens. Time course studies showed a dramatic induction of IL-12 p40 mRNA 4 h after in vivo allergen treatment reaching peak strength after 6 h. In cell depletion assays we show that epidermal keratinocytes are the major source of this cytokine in the epidermis. This was further supported by analysis of mRNA derived from the human keratinocyte cell line HaCat expressing IL-12 p35 and p40 mRNA upon stimulation. The presence of bioactive IL-12 in supernatants derived from allergen-stimulated epidermal cells was demonstrated by IL-12-specific bioassay. Additional evidence for the functional importance of IL-12 in primary immune reactions in skin was obtained in allogeneic proliferation assays using human haptenated epidermal cells containing Langerhans cells as APC and allogeneic CD4+ T cells as responders. Anti-IL-12 mAb inhibited the proliferation of T cells by 50%. In aggregate our data demonstrate that nonlymphoid keratinocytes are capable of producing functional IL-12 and provide evidence for the functional significance of IL-12 in primary immune responses in skin. (J. Clin. Invest. 1994. 94:1799-1805

In Vitro and In Situ Expression of IL-23 by Keratinocytes in Healthy Skin and Psoriasis Lesions: Enhanced Expression in Psoriatic Skin

“…1, nonstimulated keratinocytes from both normal and psoriatic lesional skin displayed mRNA for IL-23 p19 and IL-12/IL-23 p40, indicating that these cells constitutively express the two subunits of IL-23. In addition, we also demonstrated the constitutive presence of IL-12 p35 mRNA, confirming earlier studies (12,19,20).…”

Further studies on the role of IL-12 in Pseudomonas aeruginosa corneal infection

“…IL-12 appeared to be generated by keratinocyes, as it persisted when immune cells were depleted from the preparation. 27 In the light of the above, as well as previous data from our laboratory, 7,9 we next hypothesized that administration of exogenous rIL-12 might lead to enhanced IFN-g and TNF-a production, resulting in increased pathogenesis and corneal perforation. At 1 day p.i., similar corneal disease was detected in both rIL-12-and PBS/BSA-treated BALB/c mice, but significant differences were observed at 3, 5 and 7 days p.i.…”

Granulocyte/Macrophage Colony-Stimulating Factor Inhibits IL-12 production of Mouse Langerhans Cells

“…2, mouse LC spontaneously secreted IL-12 p40 in a time-dependent manner for up to 48 h in our system. In contrast, KC cultured in the same way produced only a small level of this protein (data not shown), although stimulated KC are also capable of producing IL-12 (25).…”