In vitro analyses of immune responses to metal and organic haptens in humans with contact allergy

Sammanfattning: Contact allergy is one of the most common skin diseases with great social and economical impact. The origin and nature of contact allergens (haptens) capable of inducing T-cell mediated allergic reactions are diverse, ranging from organic molecules to metal ions. Most of the current knowledge on T-cell responses to haptens in humans with contact allergy have been established by studies on the metal ion nickel (Ni), the most common cause of contact allergy, whereas reactivity to the large group of organic haptens has been less studied.Haptens are not immunogenic by themselves but must bind carrier molecules prior to their presentation on MHC class I or II molecules and subsequent recognition by T cells. Due to differences in their chemical nature, haptens interact with host molecules by different mechanisms and differences in their solubility can influence their access to different antigen-presenting pathways.The aim of the present study was to define immune responses elicited by haptens of different chemical nature including Ni (hydrophilic metal ion), methylisothiazolinones (hydrophilic organic molecule) and parthenolide (lipophilic organic molecule). The immune response displayed by subjects with allergy to these substances, and non-allergic control subjects, was assessed by measuring hapten-induced cytokine production in peripheral blood mononuclear cells (PBMC) with a focus on ELISpot analysis of T-cell type 1 (e.g. IFN-g and IL-2) and type 2 (e.g. IL-4, IL-5 and IL-13) cytokines. For Ni and parthenolide, the phenotype of the hapten-reactive T cells was determined. The allergic status of subjects was defined by clinical history and patch testing. The latter is the established diagnostic method for contact allergy, based on applying various haptens to the subjects’ back and grading the skin reaction after 2-3 days.All three haptens elicited a concomitant T-cell type 1 and 2 response in subjects with contact allergy to the corresponding hapten, suggesting the induction of a functionally related cytokine profile, irrespective of the chemical character of the hapten. The cytokine response was related to the degree of the subjects’ patch test reactivity; PBMC from a vast majority of subjects with strong and moderate patch test reactivity displayed detectable cytokine responses to the corresponding haptens, whereas subjects with weak or no (controls) patch test reactivity did not. Despite the similar cytokine profile induced, the phenotype of the reactive T cells was found to differ between haptens with Ni eliciting CD4+ T cells and parthenolide eliciting CD8+ T cells. This difference may be explained by a better ability of a lipophilic hapten to gain access to the MHC class I-restricted antigen-presentation pathway. Moreover, the data suggest that analysis of cytokine responses to haptens may facilitate future development of in vitro-based diagnostics assay for contact allergy.Finally, the relationship between the variation over time in patch test reactivity and systemic reactivity to Ni, in terms of cytokine responses to Ni in vitro, was investigated. The degree of patch test reactivity is known to vary over time, in particular in subjects with weak reactivity. Ni-allergic subjects were patch tested three times with three month intervals and PBMC obtained at the same time points were assessed for in vitro reactivity to Ni. The overall reactivity in the patch test and the in vitro test was well correlated confirming that both methods provide a good and comparable estimate of the systemic reactivity to Ni. However, fluctuations in the patch test reactivity over time were not well correlated with variations in the cytokine response elicited in vitro suggesting that other parameters besides changes in the systemic reactivity could significantly contribute to the variation in patch test reaction over time.