Are skin sensitisation test methods relevant for proteins?

Tests for identification of chemical skin sensitisation hazard have been available for decades, evolving from guinea pig assays, through the first validated method, the local lymph node assay, to several validated in vitro methods. These methods successfully identify the hazard for chemicals, with an accuracy in the region of 85%. However, in some regulations, consideration may be given to their application to proteins. Here, the scientific relevance of the use of skin sensitisation tests for the assessment of the allergenic potential of proteins is reviewed and considered in the context of both: (a) what is known of the allergenic properties of proteins compared with chemicals, and (b) current understanding of the extent to which proteins actually give rise to contact allergy. There is no doubt that many foreign proteins can behave as respiratory sensitisers and food allergens, and that certain proteins can also cause cutaneous allergy via skin contact, typically mediated via immunoglobulin E (IgE) antibody. However, the absence of any specificity in predictions from existing skin sensitisation test methods, together with the lack of a suitable body of either positive or negative controls, dictates that use of these tests with proteins is without any scientific justification or predictive merit.