In this study, the author examined the cross-reactivities of Stachybotrys chartarum, Aspergillus niger/fumigatus, and Penicillium notatum with affinity-purified rabbit sera. The molds were grown for expression of maximum numbers of antigens, after which they were extracted and mixed with commercially available extracts. The mixture was used for antibody preparation in rabbits, measurement of antibody levels, and for the demonstration of the degree of cross-reactivity. Control rabbits were injected with saline, yet they produced significant levels of immunoglobulin G antibodies against all mold extracts tested. The author interpreted this result to mean that sera obtained from rabbits immunized with pure mold extracts likely reflected cross-reactivity with other molds. Therefore, only affinity-purified antibodies and the most sensitive immunoassay technique (i.e., enzyme-linked immunosorbent assay [ELISA]) were used for the cross-inhibition studies.
The antigenic cross-reactivities were as follows: (a) between Aspergillus and Penicillium, 19.6-21.0%; (b) between Stachybotrys and Aspergillus, 8.2-8.7%; and (c) between Stachybotrys and Penicillium, 7.0-9.6%. The findings of this study demonstrate that cross-reactivity studies between different molds require the use of affinity-purified antibodies and a sensitive and quantitative assay with untreated antigens. With the use of such an assay, it was determined that the cross-reactivity between Stachybotrys, Aspergillus, and Penicillium was at approximately 10%, which is less widespread than previously believed.