Mushroom plant workers experience a shift towards a T helper type 2 dominant state: Contribution of innate immunity to spore antigen

Contemporary mushroom factories are places where there is a substantial risk of the occurrence of respiratory allergy. The aims of this investigation were to estimate its causative agents and to evaluate the contribution of innate immune response in mushroom workers who cultivate Hypsizigus marmoreus (Bunashimeji). Cross-sectional and follow-up studies were performed in the factory. We investigated CD1b, CD3, CD4, CD8, CD14, CD45RO, CD62L and CD161 expression in peripheral blood mononuclear cells (PBMC) by flow cytometry, and serum levels of interleukin (IL-2), IL-4, granulocyte-macrophage colony stimulating factor (GM-CSF), IL-13 and interferon (IFN)-γ by enzyme-linked immunosorbent assay (ELISA). Co-culture experiments of PBMC with spore extracts were also performed. Percentages of CD1b⁺ monocytes, natural killer (NK), NK T and CD4⁺ T cells were increased in the workers compared with controls. Increases in Th2 type cells, Th2/Th1 ratio and serum IL-13 and decreased IFN-γ were detected, indicating a Th2-biased status of the workers. The follow-up study showed that monocytes and NK cells increased soon after employment while CD4⁺ T, Th2 and NK T cells increased gradually as employment time lengthened. Serum precipitating antibody to the mushroom antigen could be detected at a later stage. Co-cultivation of PBMC with the spore extracts induced much higher CDIb expression, and suppressed secretion of Th1 cytokine in culture supernatants. These results indicate that the mushroom antigen contains highly immunogenic substances which stimulate PBMC into a Th2-biased in vivo status, and innate immune cells might also play a critical role in developing respiratory allergy in mushroom workers.