BACKGROUND: A possible involvement of autoimmune response to the against airway mucosa tissue in the pathogenesis of nonatopic asthma has been proposed by the earlier studies. Recently, a cytokeratin 18 protein has been identified as an airway epithelial cell autoantigen recognized by circulating IgG autoantibodies from patients with nonatopic asthma. OBJECTIVE: In this study, we evaluated an IgG subclass distribution of circulating IgG autoantibodies to airway epithelial cell proteins in the serum samples from adult patients with bronchial asthma. METHOD: IgG subclass (IgG1, IgG2, IgG3, and IgG4) autoantibodies to airway epithelial cell proteins were detected in serum samples from patients with atopic asthma and patients with nonatopic asthma, and healthy controls by Western blot analysis. RESULT: Detection rate of IgG1 and IgG4 autoantibodies to cytokeratin 18 protein was significantly higher in patients with nonatopic asthma (3/12; 25%) compared to healthy controls (0/12; 0%) and patients with atopic asthma (0/12; 0%)(Chi-square test; P<0.05). However, there was no significant difference in the detection rate of IgG2 and IgG3 autoantibodies to cytokeratin 18 proteins among the three groups (P>0.05). CONCLUSION: The predominance of circulating IgG1 and IgG4 autoantibodies to cytokeratin 18 protein in patients with nonatopic asthma suggests a possibility of autoantibody-mediated complement activation and chronic activation of autoantigen-specific Th1 and Th2 cells.