Evidence for expression of eosinophil-associated IL-12 messenger RNA and immunoreactivity in bronchial asthma

Background: Eosinophils are a source of cytokines within the airways of ast hmatic individuals that may exert an important immunoregulatory influence. Objectives: We examined IL-12 messenger (m)RNA and protein expression in eo sinophils from peripheral blood and bronchoalveolar lavage (BAL) fluid obta ined from subjects with atopic asthma (n = 7), patients with chronic bronch itis (n = 5), and nonatopic healthy control subjects (n = 7). To further de fine this IL-12(+) population of eosinophils for the expression of other cy tokines, we colocalized IL-12 and IL-5 within the peripheral blood eosinoph ils. Methods: To detect IL-12 mRNA and protein expression, we used in situ hybri dization and immunocytochemistry techniques. The double-immunocytochemistry technique was used to localize IL-12 protein to BAL eosinophils and to col ocalize IL-5 and IL-12 in peripheral blood eosinophils. Results: IL-12 mRNA and immunoreactive protein were localized to peripheral blood eosinophils. BAL fluid-derived eosinophils from asthmatic subjects w ere also reactive to IL-12. The percentage of peripheral blood eosinophils expressing mRNA for IL-12 was significantly lower in asthmatic subjects com pared with that found in eosinophils obtained from patients with chronic br onchitis (P < .001) and control patients (P < .05). Colocalization studies demonstrated that the percentages of IL-12(+) eosinophils that are also IL- 5(+) were 72% in asthmatic subjects and only 11% in control subjects (P < . 001). Conclusion: These results suggest that eosinophils are a potential source o f IL-12. Eosinophil-derived IL-12 may contribute and modulate the local all ergic inflammatory responses.