Acute respiratory tract infections and mannose-binding lectin insufficiency during early childhood.

CONTEXT Hospital-based studies have found that increased susceptibility to certain infections is associated with low serum levels of mannose-binding lectin (MBL) due to MBL variant alleles. However, the contribution of MBL insufficiency to incidence of common childhood infections at a population level is unknown. OBJECTIVE To investigate the effect of MBL insufficiency on risk for acute respiratory tract infection (ARI) in unselected children younger than 2 years. DESIGN AND SETTING Population-based, prospective, cohort study conducted in Sisimiut, Greenland. PARTICIPANTS Two hundred fifty-two children younger than 2 years who were followed up weekly between August 1996 and August 1998 for morbidity surveillance. MAIN OUTCOME MEASURE Risk of ARI, based on medical history and clinical examination, compared by MBL genotype, determined from blood samples based on presence of structural and promoter alleles. RESULTS A 2.08-fold (95% confidence interval [CI], 1.41-3.06) increased relative risk (RR) of ARI was found in MBL-insufficient children (n = 13) compared with MBL-sufficient children (n = 239; P<.001). The risk association was largely restricted to children aged 6 to 17 months (RR, 2.92; 95% CI, 1.78-4.79) while less effect (RR, 1.47; 95% CI, 0.45-4.82) and no effect (RR, 1.00; 95% CI, 0.42-2.37) was shown among children aged 0 to 5 months and 18 to 23 months, respectively. CONCLUSION These data suggest that genetic factors such as MBL insufficiency play an important role in host defense, particularly during the vulnerable period of childhood from age 6 through 17 months, when the adaptive immune system is immature.

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