Alternaria alternata is well-known as a source of allergenic components in the cell wall and cytoplasm of conidia and hyphae that cause respiratory allergic disorders. The purpose of this study was to evaluate tissue reaction and Th 2 cytokines in mice exposed to A. alternata. A. alternata was cultured, and fungal extract was prepared by freeze–defreeze and sonication methods. BALB/c mice in one group were sensitized by two intraperitoneal injections of A. alternata extract and then intra-nasally challenged with spores suspended in sterile normal saline solution, and in another group, mice only received spores intra-nasally. Blood sampling and necropsy were performed at 1 and 72 h after spore inhalation. Histopathology demonstrated an inflammatory response with cells including lymphocytes, macrophages, neutrophils and eosinophils present and mucus hypersecretion in the lungs and airway epithelial cell hyperplasia and necrosis observed in sensitized and non-sensitized mice. Sera were analyzed by ELISA to determine serum levels of Interleukin (IL)-4 and IL-13 in immediate response and late-phase reaction, respectively. Increasing Th2 cytokine (IL-4 and IL-13) levels in the sera was also observed in the sensitized and challenged mice. The results showed that exposure to extract and then spores of A. alternata induced rapid and highly elevated production of IL-4 and IL-3. These cytokines were associated with respiratory histopathological changes.

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