BACKGROUND

Quantitative relationships between immunological reactivity, non-specific bronchial responsiveness and bronchial responsiveness to allergens have scarcely been investigated in occupational asthma.

METHODS

We assessed the above relationships in 24 subjects with baker's asthma. The skin endpoint titration to bakery allergens as a measure of immunological reactivity, together with the methacholine PC20 and allergen PC20 during early asthmatic reaction were determined.

RESULTS

All patients had positive skin tests to some bakery allergens (wheat and rye flour, soybean flour, fungal enzymes and egg white proteins) and bronchial hyperresponsiveness to methacholine. Specific inhalation challenge (SIC) tests were performed with aqueous allergen extracts of cereal flour (n = 14), soybean (n = 8), baking enzymes (n = 12), and egg white proteins (n = 8) in sensitized workers. A positive asthmatic reaction was observed in 84% of the inhalation challenges. SIC elicited isolated early asthmatic reactions in 62%, dual reactions in 32% and isolated late reactions in 5%. Multiple linear regression analysis showed allergen PC20 as a function of skin sensitivity to allergen and methacholine PC20, yielding the following highly significant regression formula: log-allergen PC20 = 0.18 + 0.99 log(skin sensitivity) + 0.343 log(methacholine PC20) (r = 0.89, P < 0.001). This formula predicted allergen PC20 to within one double concentration in 67%, to within two double concentrations in 85% and within three double concentrations in 97%.

CONCLUSION

The main determinant of bronchial responsiveness to allergen in patients with baker's asthma is the degree of sensitization to occupational allergens as determined by skin reactivity, modulated to a lesser extent by non-specific bronchial hyperresponsiveness.