Diagnosis in vitro of contact allergy to nickel: Th2-skewing of PBMC cultures improves the detection of allergen-specific lymphocyte response

The aim of this study was to determine whether skewing of lymphocytes from allergic patients towards Th1- or Th2-type could improve in vitro detection of nickel-specific cells using enzyme-linked immunospot assay (ELISPOT) , enzyme-linked immunosorbent assay (ELISA), and lymphocyte proliferation test (LPT).

Methods: PBMC from 14 patients with allergic contact dermatitis (ACD) to nickel and 14 non-allergic donors (controls) were analysed for their response to nickel (Ni). IFN-γ and IL-2 ELISPOT was performed without and with addition of Th1-skewing cytokines (IL-7 + IL-12). IL-5 and IL-13 ELISPOT was done without and with Th2-skewing cytokines (IL-7 + IL-4). Parallel to this, ELISA for IFN-γ and IL-5, and LPT was carried out.

Results: Without skewing, the median number of cells secreting IL-5 in response to Ni was 10 cells per 1 million PBMC in ACD patients and 0 in non-allergic controls (p=0.007). After Th2-skewing, the numbers were 140 in ACD and 15 in controls (p=0.001). A similar pattern was found in IL-13 ELISPOT. In ELISA, median IL-5 concentrations were without skewing 14 pg/1 million PBMC in ACD and 0 in controls (p=0.001), and with skewing 266 and 33 respectively (p=0.014). The median number of cells secreting IL-2 in response to Ni was greater in ACD (67.5) than in controls (7.5; p=0.001), with no influence of Th1-skewing. As for Th1 response, there was a higher IFN-γ output and more secreting cells among PBMC from ACD patients, but the difference to the controls remained non-significant both with and without Th1-skewing. The best LPT performance was observed without addition of skewing cytokines.

Discussion: It is generally accepted that ACD is associated with Th1-type response to allergens. A few recent studies showed that Th2 response could also be detected. Our results suggest that Th2 response in vitro discriminates Ni-allergic from non-allergic persons better than Th1 response. It is possible that conditions in vitro favour the development of memory cells into Th2 phenotype. Moreover, Th2-skewing by addition of IL-7 and IL-4 further amplifies allergen-specific IL-5 response, expressed as an increase in both the number of secreting cells and the amount of secreted cytokine. The difficulty of detecting a significant Th1 response might be due to the high spontaneous production of IFN-γ by various PBMC fractions (e.g. by NK cells), which possibly could obscure the Ni-specific IFN-γ secretion.

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