Background: To diagnose baker's asthma, occupational sensitization to wheat flour should be distinguished clearly from influences of cosensitization such as it may exist in pollinosis patients. To define the route of sensitization, the cross-reactivity between wheat flour and grass pollen allergens was investigated.
Methods: Two groups of atopic individuals with or without professional contact to wheat flour were screened by skin prick test for their sensitization to wheat flour and grass pollen and, in the case of hints for cosensitization, by Enzyme Allergo Sorbent Test (EAST). Cross-reactivity between wheat flour and grass pollen allergens was investigated by IgE binding inhibition assay using sera of 20 cosensitized individuals and by immunoblots.
Results: The immunological cross-inhibition between wheat flour and grass pollen proves some proteins to share common allergenic determinants. Significant differences between bakers and individuals not occupationally exposed to flour could be seen in the inhibition of IgE binding to wheat flour. While the IgE binding to wheat flour allergens was only slightly inhibited by grass pollen proteins in baker's sera its inhibition was nearly complete by this extract in sera of nonexposed atopics. Immunoblots indicate that wheat proteins with a molecular weight of about 8-12 and 22 kD preferentially react with sensitized bakers' IgE and not with IgE of other individuals. IgE binding to grass pollen allergens in immunoblots and inhibition experiments showed no differences between bakers and other subjects.
Conclusion: In the group of atopics without professional contact to flour, the positive test results from wheat flour obviously ensue from contact to cross-reacting grass pollen proteins whereas bakers are exposed and sensitized to allergens of both sources. Such cross-inhibition experiments help to identify the source of sensitization which may be difficult to obtain in case of cross-reacting allergens.