Comparison of respiratory responses to Metarhizium anisopliae extract using two different sensitization protocols

Metarhizium anisopliae, an entomopathogenic fungus, is a prototypic microbi al pesticide licensed for indoor control of cockroaches, a major source of allergens. We have previously demonstrated allergy and asthma-like response s in BALB/c mice intraperitoneally (IP) sensitized in the presence of adjuv ant and intratracheally (IT) challenged with the soluble factors from M. an isopliae crude antigen (MACA) (Ward et al., 1998, 2000). This protocol has been used frequently to establish animal models of allergenicity. However, the sensitization protocol is artificial and not representative of an envir onmental exposure. Concern has been raised that this protocol might produce allergic responses that would not occur under normal environmental exposur e conditions. The objective of this study was to compare responses in mice to MACA by two exposure protocols: (1) exclusive respiratory exposures with out adjuvant (representative of environmental exposures) and (2) intraperit oneal sensitization in the presence of adjuvant followed by IT challenge (t he traditional approach). The intratracheal protocol consisted of four IT e xposures of 10 mu g MACA in 50 mu l HBSS each over a 4-week period. A vehic le control group of mice was exposed IT to HBSS. The intraperitoneal protoc ol consisted of IP sensitization with 25 mu g MACA in 0.2 ml of 1.3% alhydr ogel (aluminum hydroxide) followed 14 days later with an IT challenge (10 m u g MACA/50 mu l HBSS). Airway reactivity responsiveness to methacholine wa s assessed, serum and bronchoalveolar lavage fluid (BALF) samples were obta ined, and the lungs were fixed for histopathology at 1, 3, and 8 days Follo wing the last MACA IT challenge. Both groups exhibited immune and pulmonary responses typical of allergic asthma. In general, local responses in the l ung, including inflammatory responses (eosinophils, lymphocytes, and macrop hages), BALF IgE, and functional responses to methacholine were greater in the IT sensitized group compared to the IP sensitized group, whereas the sy stemic IgE response was greater in the IP sensitized group. The BALF IL-5 c ytokine levels were elevated before and throughout the eosinophil influx. I L-4 was detected in the BALF of IP sensitized, but not IT sensitized mice. Histopathologic changes in the two groups were similar in nature but more s evere in the IT mice. The results suggest that the IP sensitization protoco l does not induce the level of respiratory responsiveness that results from sensitization by a physiologically relevant route of exposure. Thus total serum IgE levels, which were greater following IP sensitization, may not be the best indicator of allergen potency, at least with respect to respirato ry responses. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.