Predominance of the major allergen (Alt a I) in Alternaria sensitized patients

Thirty-nine patients sensitized to Alternaria were evaluated using titrated skin-prick test (SPT), histamine release studies (HR), inhibition of RAST and immunoblotting studies. To determine the relevance of the major allergen, Alt a I, specific rabbit antibodies against Alt a I and Alt a B were used. The antibodies were preincubated at different concentrations: (i) with the Alternaria allergen dose required for maximum response in the HR assay (10 BU/ml) and (ii) with the Alternaria antigen coupled to RAST paper discs (1000 BU/disc). Dose dependent inhibition of histamine release (n = 30, mean = 80% +/- 4%, IC30 = 0.69 micrograms/ml) and of RAST (n = 7, IC30 = 4.4 micrograms/ml) was found in all patients sensitized to Alternaria as indicated by allergen induced HR. The greater the response to Alternaria in HR, the higher the antibody concentrations necessary for inhibition (P < 0.05). Immunoblot experiments (n = 25) using SDS-PAGE showed in all cases IgE- and IgG binding at approximately 28 kD, which is the size reported for the major allergen, Alt a I. In two cases, slight IgE binding at 45 and 66 kD was also found, while in two other patients, only IgE binding at 66 kD was seen. Our findings emphasize the major importance of Alt a I in patients sensitized to Alternaria.