Dictionary of Allergies .. Contact allergens

Contact allergens

Contact allergens are small chemicals that easily penetrate epidermal skin and that are able to sensitize part of the human population. After sensitization repeated contacts lead to chronic delayed type of hypersensitivity reactions mediated by CD4+ T lymphocytes resulting in development of contact eczema. The interaction of contact allergens with CD4+ T cells was studied with panels of nickel-specific CD4+ T lymphocyte clones (TLC) of nickel-allergic and nonallergic individuals. Nickel recognition by many TLC from the patients and all TLC from a nonallergic control individual was HLA-II restricted with a wide variety of restriction determinants on either HLA-DR, HLA-DQ or HLA-DP molecules. Nickel presentation to many TLC did not require carrier proteins or intracellular processing by the APC, indicating a direct interaction with HLA-II molecules.

These observations suggest that the allergic potential of molecules such as nickel ions results from direct interactions with various molecules that are critical in antigen recognition and T cell activation. They do not explain development of contact allergy, since there was no difference in nickel recognition by the majority of nickel-specific TLC from the patients and the nonallergic control. Development of disease was also not associated with unbalanced lymphokine production. Nickel-activated TLC from the allergic patients and the control both were Th1 cells that secreted interleukin (IL-2), IFN-γ, GM-CSF and TNF-˜ and low levels of IL-4 and IL-5. In addition, the Th2 Dp-specific TLC from the atopic donors were strong inducers of FcœRII/CD23 expression on APC, implying the induction of strongly facilitated local atopen-presentation in individuals with elevated levels of IgE reacting with the same atopens.

References

Kapsenberg, M.L., et al: Allergen-specific CD4+ T lymphocytes in contact and atopic dermatitis. In the Skin as Immune Organ: Annual Meeting of EAACI, Zurich, Switzerland, May 25-29, 1991.