IgEmediated Immediate Allergic Reactions

Data from standard toxicology studies yield little information on the ability of a test compound to induce immediate hypersensitivity in the skin or lung. Two types of molecules can initiate hypersensitivity reactions. High-molecular-weight proteins are common allergens. Low-molecular-weight chemicals (LMWC) are haptens and must bind to protein to elicit an immune response.

It is possible to define the allergic potential of LMWC using a multilevel or tier approach to testing. In Tier 1 studies, structure-activity relationships in known classes of allergens are ascertained. In addition, the theoretical covalent protein-binding capacity of the chemical is determined. In Tier 2, the actual chemical-protein binding is defined in vitro assays and the results expressed as the moles of hapten bound per mole of protein. If the chemical binds to protein and creates a putative antigen, guinea pigs are immunized to determine the immunogenicity of the class of antibody produced to the chemical (Tier 3).

Finally, the allergenicity is determined in a guinea pig inhalation model (Sarlo and Clark, 1992). Tests are conducted that determine (1) whether the chemical has the potential to cause allergic reactions via the inhalation route, (2) the no observable adverse effect level (NOAEL) with respect to allergic symptoms, and (3) the dose response relative to the reference chemicals known to cause allergic reactions by the inhalation route. If the responses of the two materials are the same, then consumer and occupational exposures to the new material are set at the same level as those for the historical ones. If the responses are different, then adjustments in exposure are made accordingly.

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