Serum IgG subclasses in patients with an increased susceptibility to respiratory tract infections.

Abstract Serum IgG subclass concentrations were assayed in 45 patients with chronic respiratory tract infections and 16 patients with recurrent acute respiratory tract infections. Eleven of these 61 patients, all but one with recurrent acute infections, were IgA‐deficient but the remainder had normal or high serum immunoglobulin concentrations. Only 4% of patients with chronic infections were lgG2‐deficient. The prevalence of lgG2 deficiency amongst patients with recurrent acute infections was greater (31%), but in most cases this appeared to be due to an association with IgA deficiency. Owing to the limits of assay sensitivity it was not possible to determine whether any patient was lgG4‐deficient, but the number of sera with undetectable lgG4 was greater in patients with recurrent acute infections than in controls (37.5%vs 10%, p<0.01), although such patients were mainly those with IgA and lgG2 deficiency. None of the patients had IgGl or lgG3 deficiency; in fact lgG3 concentrations were higher than those of controls in both groups of patients (ρ<0.001) and IgGl concentrations were higher than those of controls in patients with recurrent infections (ρ<0.01). Thus, unequivocal IgG subclass deficiency is uncommon in non‐lgA‐deficient patients, but those with lgG2 deficiency may have an immune defect requiring further investigation.