Allergic responses to the biopesticide Metarhizium anisopliae in Balb/c mice

Metarhizium anisopliae is used as a microbial pesticide to control cockroaches and other insects. M. anisopliae has demonstrated neither infectivity nor toxicity in mammals. However, allergenicity has not been assessed. M. anisopliae is a prototype for other organisms released into the environment for pesticide or other beneficial applications. Hence this study is part of an effort to develop methods for screening such organisms for allergenic potential. Soluble factors from fungal components were combined in equal protein amounts to form a crude fungal antigen (MACA). Balb/c mice were intratracheally (IT) challenged with 25 micrograms fungal antigen 13 days post intraperitoneal sensitization with the fungal antigen in alhydrogel adjuvant. Additionally, mice were sensitized with adjuvant alone or chitin media in adjuvant as experimental controls. Serum and bronchoalveolar lavage fluid (BALF) were harvested prior to challenge and at 1 and 7 days post IT challenge (DPIT). These mice exhibited immune and pulmonary inflammatory responses to MACA characteristic of allergy. Total serum IgE for antigen-sensitized animals increased 7.6- and 14.7-fold over that for chitin media and adjuvant controls, respectively, at 7 DPIT. Less striking increases were seen at 24 DPIT and prior to challenge. BALF IL-4 was dramatically elevated only in MACA-sensitized and challenged mice and only at 1 DPIT. Additionally, there was a dose-dependent increase in BALF eosinophils from MACA-sensitized mice at both 1 and 7 DPIT. While lymphocyte counts were increased for all treatment groups at 1 DPIT, by 7 DPIT lymphocyte counts for MACA-sensitized mice only were significantly elevated compared to controls. Pulmonary inflammation, edema, and cell damage were apparent at 1 DPIT (25 micrograms MACA), as indicated by a neutrophilic influx and elevated levels of total protein and LDH, in both sensitized and control groups. These effects were significantly decreased, but not eliminated by reduction of the challenge dose to either 10 or 5 micrograms MACA. While BALF IL-4 was also reduced at the lower challenge doses, eosinophilia and total IgE were unchanged. The data suggest that the crude fungal extract MACA contains one or more potent allergens and that total IgE may be useful in the identification of the allergen(s).