Chemicals and proteins as allergens and adjuvants.

Small molecular weight chemicals may irritate tissues via the induction of the production of various proinflammatory and chemotactic molecules. The structure of these irritants is heterogenous, as is the pattern of their effects. Chemicals are potentially allergenic (i.e. haptens) when they are able to bind proteins such as immune response molecules. Sensitization will occur when these haptens additionally induce irritation resulting from an intrinsic adjuvant's activity of the chemical. In most cases haptens induce the activation of hapten-specific T cells with a type 1 cytokine profile mediating delayed hypersensitivity. A limited number of haptens induce the production of type 2 cytokines in T cells and, consequently, allergic reactions after inhalation. Similarly, inhaled proteins become allergenic when they activate protein allergen-specific T cells producing type 2 cytokines. In many individuals this cytokine profile is associated with atopy. It must be expected, however, that a type 2 cytokine profile can also be inflicted by the action of various adjuvants types, such as biologically active small molecular weight chemicals and proteins (i.e. enzymes) and microorganisms, thereby promoting allergic reactions.