Differential induction of cutaneous TNF-α and IL-6 by topically applied chemicals

Background: Increasing evidence shows that contact allergens and skin irritants can induce or upregulate the cutaneous expression of cytokines, including those that are required for the initiation of immune responses and which participate in inflammatory reactions. Objective: The present investigation compared the ability of the skin allergens oxazolone and 2,4- dinitrochlorobenzene (DNCB) and the skin irritant benzalkonium chloride (BZC) to stimulate the cutaneous expression of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in mice. Results: Each chemical tested induced the dose-dependent production of IL-6 with similar kinetic profiles. BZC was less effective at provoking increases in this cytokine; concentrations (1%) that caused marked edema failed to stimulate significant changes in IL-g expression. Under conditions of topical expo sure in which each of these chemicals caused a vigorous inflammatory response in the skin, as measured by induced edema and the increased production of IL-6, only oxazolone and DNCB stimulated expression of TNF-α. The failure of BZC to initiate TNF-α production in the skin was not attributable to inhibition of the bioassay used to measure this cytokine and was apparently independent of the stimulation by this chemical of TNF-α inhibitory factors. Conclusion: These data indicate that not all chemicals that have the ability to cause skin irritation and cutaneous inflammation will elicit detectable TNF-α responses and that characterization of cutaneous irritants and allergens on the basis of induced cytokine expression patterns in the skin must be approached with caution.