The significance of IgG subclasses and mannan-binding lectin (MBL) for susceptibility to infection in apparently healthy adults with IgA deficiency

The aim of this study was to investigate the significance of IgG subclasses and MBL for susceptibility to infection in association with IgA deficiency . The study population consisted of 139 apparently healthy adult blood dono rs with IgA deficiency and normal serum levels of IgG and IgM, and an incre ased susceptibility to infection demonstrated at a population level. Additi onally, 216 controls matched for age and sex were investigated. IgG4 defici ency was more common and the mean level of IgG4 lower in persons with IgA d eficiency than in the controls. No significant associations could be demons trated between overt IgG subclass deficiencies and increased susceptibility to infection. However, when the mean concentrations of IgG subclasses were analysed with regard to medical history, that of IgG1 was lower in persons who reported recurrent viral respiratory infections, that of IgG3 in perso ns who had episodes of severe infection in their history, and that of IgG4 in persons who had recurrent mild respiratory infections, compared with tho se who had no particular history of infections. In contrast, MBL deficiency -alone or combined with that of the IgG subclass-was not associated with in creased susceptibility to infection in persons with IgA deficiency. The res ults indicate that the proneness to infections observed in a population of otherwise healthy persons with IgA deficiency can only for a small part be accounted for by concomitant deficiencies of IgG subclasses. Contrary to ex pectations, no synergism between the deficiencies of IgA and MBL could be d emonstrated.