Failure to detect deposition of complement and immunoglobulin in allergen-induced late-phase skin reaction in atopic subjects

Type III allergy skin testing. Position statement for EAACI Subcommittee on Skin Tests and Allergen Standardization

Immune-complex-mediated hypersensitivity has been implicated in a small number of allergic respiratory conditions. These include EAA and ABPA. In addition, there is some evidence of type IV hypersensitivity in EAA and BFL, together with activation of complement via the alternative pathway (4, 8, 26). Positive immediate skin tests are now usually regarded as an essential criterion for the diagnosis of ABPA. These reflect the presence of antigen-specific IgE, but this test is not specific for ABPA, as other atopic subjects may also be sensitized to A. fumigatus without any evidence of the parenchymal features that are required to diagnose ABPA. For FL, skin tests with currently available antigens show poor discrimination between affected patients and exposed but healthy individuals. There is little evidence that vascular deposition of immune complexes in the skin contributes to the delayed skin responses in EAA, and skin tests in FL are not specific for type III hypersensitivity. Further refinement of methodology and antigen extracts may improve the specificity of skin tests in FL, but in many cases the aetiology of EAA is multifactorial and the true causative antigens may not have been identified. Therefore, the diagnosis of EAA remains based on history and clinical findings, supported by the presence of precipitins, and sometimes by bronchial biopsy and lavage appearances (25).