IgG subclass deficiency in children with IgA deficiency presenting with recurrent or severe respiratory infections.

A group of 22 children presenting with recurrent or severe respiratory tract infections who had low IgA levels (more than 2 SD below the mean for age) were examined for IgG subclass deficiency. Patients were screened for possible defects in neutrophil chemotaxis, bactericidal, fungicidal, and quantitative iodination activity, as well as for complement function. The majority of the patients showed IgG subclass levels below the mean for age. Nine of the children showed definite IgG subclass deficiency and at least two showed definite deficiency of more than one IgG subclass. The predominant subclass deficiency was found to be IgG1. While nine children showed IgG4 levels below the level detectable by the technique used, it is not possible to assess whether these patients are deficient in this isotype since some healthy subjects also give values below the level of detection. Most of the patients who had very low (1-6 mg/dl) or undetectable (less than 1 mg/dl) levels of serum IgA did not show IgG subclass deficiencies, while IgG subclass deficiencies were common among those with borderline low IgA levels (slightly more than 2 SD below the mean for age). Nine children showed total IgG levels close to 2 SD below mean for age, and at least six of these showed IgG subclass deficiency. The result suggests that patients with recurrent and/or severe respiratory infections who have borderline IgA and IgG levels may have IgG subclass deficiencies and if they do could benefit from immunoglobulin therapy.