Background: Respiratory infections are major causes of morbidity and mortality, but determinants of susceptibility are poorly defined. We studied whether and to what extent immunologic and genetic factors are associated with increased susceptibility to respiratory infections.
Methods: We evaluated the prevalence of IgA, IgM, IgG, and IgG subclass deficiencies, impairment in the antibody response against pneumococcal polysaccharides, G2m(n) allotypes, Fc gamma RIIa polymorphisms, partial C2 and partial C4 deficiency, promoter polymorphisms in MBL2, and lymphocyte subset deficiencies in a control population and in consecutive children with recurrent respiratory infections.
Results: IgA and/or IgG subclass deficiency was found in 27 of 55 patients (49%) and 6 of 43 controls (14%) (P = 0.0006). An impaired antibody response to polysaccharides was found in 7 patients (19%) and in 0 of 37 controls (P = 0.002). The Gm(n)marker was absent in 25 of 55 patients (45%) and 6 of 42 controls (14%) (P = 0.009). The MBL2 variants O/O, A/O, and A/A occurred in 9, 14, and 32 of the 55 patients, respectively, and in 1, 19, and 23 of the 43 controls, respectively (P = 0.05). There was no increase in the prevalence of partial C4 deficiency, C2 deficiency, lymphocyte subset deficiency, or Fc gamma RIIa polymorphism in the patients compared to the controls. A combination of at least 2 immune defects was found in 31 of 55 patients (56%) and in 4 of 42 controls (11.6%) (P <0.0001).
Conclusion: Specific antipolysaccharide antibody deficiency, IgA and/or IgG subclass deficiency, Gm(n) allotype, and MBL2 genotype are susceptibility factors for recurrent respiratory infections, and coexistence of several immune defects is the strongest risk factor in this study.