Allergen-induced changes in interleukin 1 beta (IL-1 beta) mRNA expressionby human blood-derived dendritic cells: Inter-individual differences and relevance for sensitization testing

The development of in vitro methods for the identification of skin sensitiz ers based upon analysis of Langerhans cell (LC) function has been constrain ed by the fact that these cells represent only a minority population in the skin that, once isolated, alter their phenotype spontaneously and rapidly. Methods have been developed recently that allow the expansion in culture u sing appropriate cytokine conditions of LC-like dendritic cells (DCs) from certain tissues, including human peripheral blood. It has been demonstrated that culture of human blood-derived LC-like cells with selected potent con tact allergens such as 2,4-dinitrofluorobenzene (DNFB) stimulates selective phenotypic changes, including the upregulation of interleukin 1 beta (IL-1 beta) mRNA expression, under conditions where skin irritants are without e ffect. However, in our own previous investigations, we have observed that t here appear to be differences between blood donors with respect to the resp onsiveness of DCs to DNFB-induced changes in IL-1 beta expression, differen ces that could compromise the utility of this approach as a screening metho d For contact allergens. We have therefore investigated donor variability i n DC responsiveness to a panel of known human contact allergens (DNFB; para phenylene diamine, PPD; methylchloroisothiazolinone/nlethylisothiazolinone, CMIT), to the skin irritant benzalkonium chloride and to the mitogen phorb ol myristate acetate (PMA), Dendritic cells derived from all donors express ed IL-1 beta mRNA constitutively. Treatment of DCs isolated from donors wit h a responder phenotype to DNFB with PPD or CMIT resulted also in up-regula tion of IL-1 beta mRNA expression, although such changes were always compar atively modest, generally resulting in a twofold induction compared with ve hicle-treated controls, Dendritic cells derived from donors with a non-resp onder phenotype to DNFB failed also to respond to these additional contact allergens under conditions where the mitogen PMA caused similar increases i n IL-1 beta expression to those observed for allergen-responsive donors. Be nzalkonium chloride failed to provoke changes in the expression of this cyt okine in any donor examined, irrespective of their responder phenotype. The temporal stability of the responder/non-responder DC phenotype was confirm ed, with stable phenotypes with respect to DNFB-induced changes in IL-1 bet a mRNA expression observed over a period of some 18 months. Fifty per cent (6/12) of donors tested over this period displayed a responder phenotype. T hese data demonstrate that chemical allergens do stimulate consistent chang es in IL-1 beta mRNA expression in the proportion of donors who have a resp onsive phenotype, and that such responses are apparently selective for alle rgen using the relatively narrow range of materials assessed to date. Howev er, the modest response to very strong contact allergens, coupled with the difficulties of responder/non-responder phenotypes, means that in its prese nt form this approach does not tend itself to the routine assessment of ski n sensitizing activity. Copyright (C) 2001 John Wiley & Sons, Ltd.