Differential allergy responses to Metarhizium anisopliae fungal component extracts in BALB/c mice

Intratracheal aspiration (IA) exposure to Metarhizium anisopliae crude antigen (MACA), which is composed of equal protein amounts of mycelium (MYC), conidia (CON) and inducible proteases/chitinases (IND) extracts/filtrates, has resulted in responses characteristic of human allergic asthma in mice. The study objective was to evaluate the potential of each component extract to induce allergic/asthma-like responses observed in this mouse model. BALB/c mice received 4 IA exposures to MACA, CON, MYC, IND, or bovine serum albumin (BSA; negative control) or appropriate vehicle control or inflammatory control over a 4-wk period. Mice were assessed by whole-body plethysmography for immediate airway responses and airway hyperresponsiveness to methacholine (Mch) challenge (PenH). Serum and bronchoalveolar lavage fluid (BALF) were collected 3 d after the final exposure. Additionally, BALF neurotrophin levels and extract protease and chitinase activity levels were evaluated. Western blot analysis showed that each component contained different IgE-reactive proteins. All fungal extract exposures resulted in elevated BALF total and differential cell counts, IgE and IgA and total serum IgE compared to HBSS and BSA controls. MYC-exposed mice had the highest responses except for neutrophil influx, which was highest in MACA and IND exposures. However, the MYC-exposed mice had significantly lower PenH values compared to other treatments. By comparison IND and MACA induced significantly higher PenH values. Additionally, IND had substantially higher protease activity levels but induced the lowest neurotrophin levels compared to the other fungal exposures. In this allergic asthma model extract chitinase activity was not associated with allergic responses. In summary, multiple exposures to any of the M. anisopliae component extracts induced allergic/asthma-like responses in BALB/c mice but the response magnitude was different for each component and each appears to contain unique IgE-reactive proteins. Therefore, hazard identification and/or risk assessment for molds must test both mycelia and conidia.