Characterization of exposure to low levels of viable Penicillium chrysogenum conidia and allergic sensitization induced by a protease allergen extract from viable P. chrysogenum conidia in mice

Background: Previous evidence by our laboratory has shown that mice inoculated with viable Penicillium chrysogenum conidia or spores at levels comparable to those found in contaminated buildings induced spore antigen-specific allergic responses. We proposed that mice exposed to low levels of viable P. chrysogenum conidia would not develop allergic symptoms. We also hypothesized that the symptoms induced by high numbers of conidia were the result of sensitization to allergens released by the conidia. Methods: C57BL/6 and BALB/c mice were exposed to 1 × 10² viable P. chrysogenum conidia by intranasal instillation weekly for a period of 11 weeks. C57BL/6 mice were also sensitized to a viable P. chrysogenum conidia protease extract by intraperitoneal injections for a period of 6 weeks followed by intranasal challenge with protease extract, viable, or nonviable P. chrysogenum conidia for 2 weeks. Results: C57BL/6 mice inoculated with low numbers of conidia developed no significant lung inflammation or increased serum immunoglobulins. Mice sensitized to the protease extract and challenged with both protease extract and viable conidia produced significant increases in serum IgE and IgG1. Mice sensitized to and challenged with the protease extract developed significant eosinophilia and mucus hyperproduction as determined by bronchoalveolar lavage and histopathological examination of lung tissue. Conclusions: Mice did not develop allergic symptoms in response to challenge with low levels of P. chrysogenum conidia. Protease allergens from viable conidia induced specific allergic responses in mice, indicating the importance of P. chrysogenum conidia in allergic sensitization to the organism.