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Formaldehyde exposure enhances inhalative allergic sensitization in the guinea pig

Formaldehyde (FA), a common indoor air pollutant, has been associated with increased prevalence rates of asthmatic symptoms among exposed individuals in epidemiologic surveys. We studied the influence of FA exposure on inhalative allergic sensitization in the guinea pig. Three groups of guinea pigs (n= 12 each) were exposed to clean air or two different FA concentrations (0.13 and 0.25 ppm) over 5 consecutive days. Exposure was followed by inhalation of 0.5% ovalbumin (OA) as sensitizing allergen. Three weeks later, specific bronchial provocation with OA was performed with body plethysmographic measurement of compressed air (CA). Furthermore, specific anti‐OA‐IgGI (reaginic) antibodies were determined in serum. In a further six animals, the respiratory tract was examined histologically for signs of inflammation directly after the end of FA or clean air exposure. In the group exposed to 0.25 ppm FA, 10/12 animals were found to be sensitized to OA (positive reaction on specific provocation) vs. 3/12 animals in the control group (P<0.01). Furthermore, CA measurements of specific bronchial provocation and serum anti‐OA‐antibodies were significantly higher in the 0.25 ppm FA group than in controls (CA 0.35 vs. 0.09 ml median, P<0.01; anti‐OA‐IgC1 13 vs. <10 EU median, P<0.05), indicating enhanced sensitization. In the group exposed to 0.13 ppm FA, no significant difference was found compared to the control group. There was no sign of inflammation of the lower airways in FA‐exposed guinea pigs other than mucosal edema, which was discovered by morphometry. We conclude that short‐term exposure to a low concentration of FA (0.25 ppm) can significantly enhance sensitization to inhaled allergens in the guinea pig.