IgG subclass deficiency associated with corticosteroids in obstructive lung disease.

IgG subclass levels were measured in three groups of adult patients with obstructive airways disease to discern the relationships among depressed IgG subclass levels, chronic corticosteroid use, and recurrent sinopulmonary infections. Group 1 consisted of patients with corticosteroid-dependent bronchial asthma, group 2 patients had corticosteroid-dependent chronic bronchitis/emphysema, and group 3 was comprised of asthma patients not requiring oral corticosteroids but associated with recurrent sinopulmonary infections. One or more IgG subclass deficiencies were noted in 66.7 percent of group 1, 46.7 percent of group 2, and 6.7 percent of group 3. Significant differences were noted between groups 1 and 3 (p = .0008) and between groups 2 and 3 (p = .018), but not between groups 1 and 2 (p = .5). IgG1 deficiency was the most common subclass deficiency found; 14 (77.8 percent) of 18 patients with detectable subclass deficiency demonstrated IgG1 deficiency. In this study population, IgG subclass level deficiencies appeared to be secondary to long-term low-dose corticosteroid therapy.