New insights into the role of infection in asthma

Abstract

A growing body of evidence suggests an association between Chlamydia pneumoniae infection and asthma in some individuals. However, given that almost all individuals are infected with C pneumoniae during their lifetime, why is it that some experience asthmatic symptoms and others do not? Mannose binding lectin (MBL) is a complement-activating innate immune defense serum protein that binds sugar groups on different microorganisms. MBL has been reported to participate in protection against Chlamydia infection. Low levels of serum MBL are strongly associated with the presence of variant MBL genes encoding structural variants of the polypeptide. These MBL variants have been found to be associated with an increased risk of respiratory infections, particularly during early childhood. In the current issue of the Journal, Nagy and coworkers (p 729) report on the role of C pneumoniae infection in children with asthma, comparing them with healthy control subjects. The investigators also studied the modifying effect of MBL variant alleles on the susceptibility to asthma in children infected with C pneumoniae. In a comparison of 139 children with asthma and 174 healthy control subjects, there was no difference in the percentage who were positive for C pneumoniae–specific antibodies, in the percentage having serologic evidence of chronic Chlamydia infection, or in frequencies of different MBL alleles. However, among asthmatic children carrying variant MBL alleles, there a significantly greater number who were positive for C pneumoniae–specific IgG than among control children with variant MBL genotypes. Infected children with variant MBL alleles were found to have a higher risk of developing asthma than infected children with normal MBL genotype; this risk was especially high in children with chronic or recurrent infections. The authors conclude that their findings, if confirmed, suggest that genotyping individuals for MBL gene polymorphisms might be useful in predicting asthma risk and identifying those who are more likely to benefit from antibiotic therapy.