IGG SUBCLASS DEFICIENCIES ASSOCIATED WITH BRONCHIECTASIS

Only a small number of patients with IgG subclass deficiencies (IgGSD) have been observed to have bronchiectasis. Moreover, in the series of patients with bronchiectasis, IgGSD have not been found at any freque ncy, and the etiology of bronchiectasis remains unclear in 29 to 49% o f cases. Serum concentrations of total IgG, IgA, and IgG subclasses as well as pulmonary function were measured in 65 patients (aged: 10 to 74 yr) with bronchiectasis of unknown etiology. An ELISA test was perf ormed to quantify subclasses 1 through 4 using subclass-specific antih uman monoclonal antibodies. IgG subclass estimation in a healthy popul ation with age-stratified normal ranges was derived from 100 adults, 3 7 children aged between 10 and 12 yr, and 27 adolescents aged between 13 and 16 yr. Serum concentrations of specific IgG antibodies to Haemo philus influenzae type b capsular polysaccharide (Hib-PRP) were also a ssayed by an ELISA test in 19 of the patients (10 with IgGSD and nine with non-IgGSD) and in 58 healthy individuals before and 3 wk after im munization with Hib-PRP conjugated to meningococcal outer membrane pro tein complex (OMPC). Thirty-one patients (48%) had low serum concentra tions of one or more IgG subclasses (19 IgG2 deficiencies, 2 IgG3 defi ciencies, 3 IgG4 deficiencies, and 7 combined subclass deficiencies). All patients showed increased levels of total IgG, IgG1, and IgA, but this rise was significantly higher in patients without IgGSD. Patients with IgGSD showed impaired antibody response to Hib-PRP compared with patients with non-IgGSD and the control group. IgGSD, particularly Ig G2 deficiency, are not an unusual cause of bronchiectasis. Therefore, serum levels of IgG subclasses must be assayed whenever other causes o f bronchiectasis have been ruled out.