In order to establish the reference value of mannose-binding lectin (MBL) serum level in children and to investigate the correlation between the polymorphisms of MBL2 gene and serum MBL level in healthy Chinese of Han ethnic group and in children of Chinese Han ethnic group with recurrent respiratory tract infections (RRTI), the concentration of oligomerized MBL was measured by enzyme-linked immunosorbent assay, and MBL2 gene polymorphisms were analyzed by restriction fragment length polymorphism of polymerase chain reaction and polymerase chain reaction-sequence specific primer. The median MBL levels in the 470 normal children were 2536 ng/ml, and the P(2.5)-P(97.5) was 161-5,070 ng/ml. Our research showed that two promoter polymorphisms at -550, -221 of start codon and coding variants at codon 54 of MBL2 gene affected the protein level significantly and the most frequent genotype in Hans is HYPA/HYPA. Our results also showed that serum MBL level was significantly lower in recurrent respiratory tract infections patients compared with healthy controls (Z, -3.04, P = 0.002). The frequency of the promoter LXP haplotype and the B allele was significantly higher in RRTI patients than in controls (chi (2) 4.05, P < 0.05; OR 1.63, 95%CI 1.01 approximately 2.62; chi (2) 4.27, P < 0.05; OR 1.94, 95%CI 1.02 approximately 3.68).
Conclusion: We have established that the reference value of serum MBL level in Chinese aged between 0 and 6 years (161-5,070 ng/ml), and we found that LXP and the B are risk factors for RRTI.