| Objective To investigate the relationship between the serum mannose-binding lectin(MBL) levels,gene polymorphisms and recurrent respiratory tract infection (RRTI).Methods 110 children with RRTI,34 premature infants and 25 full-term infants were selected as the subjuect and111 normal children were selected as the control,and all of the children were Han ethnic.The serum mannose-binding lectin(MBL) level was detected by enzyme-linked immune-sorbent assay(ELISA), and the genotype,polymorphisms of code 54 and code 57 in the first exon of MBL gene were detected by the restriction fragment length polymorphism polymerase chain-reaction(PCR-RFLP).Results①The cord blood levels of MBL in the premature neonates and full-term newborns were 2.27±1.15mg/L and 3.07±1.28mg/L respectively,and the former was significantly lower than the latter(t=2.53,P＜0.05).There were no significant difference between gender in the two groups(P＞0.05);②In the control group,The levels of serum MBL in each age group were 2.83±0.93mg/L(＜1 year old), 2.92±1.14 mg/L(＜3 years old),2.80±1.18mg/L(＜6 years old) and 3.12±1.25mg/L (≥6 years old) respectively.Compared with that in the full-term newborns,there was no significant difference(P＞0.05),and there were no significant differences between the age subgroups and the gender subgroups(P＞0.05 ).③The level of serum MBL in children with RRTI(1.93±1.09mg/L)was significantly lower than that in the control group(2.98±1.05mg/L)(t=7.19,P＜0.001);The levels of serum MBL of the children in the age subgroups were 1.83±0.84mg/L(＜1 year old),1.96±0.83mg/L(＜3 years old), 1.84±1.25mg/L(＜6 years old) and 2.02±1.43 mg/L(≥6 years old) respectively,which were all lower than that in the control group(t=2.15～3.55,P＜0.01 or P＜0.05).There were no significant differences between the age subgroups.④The most common geontype in MBL gene exon 1,code 54 in Han ethnic children in Qingdao was GGC/GGC(86.7%),a homozygous wildtype,and the proportion of GGC/GAC and GAC/GAC were11.6%and 1.7%respectively.The frequency of allele GGC(0.925) was dominantly higher than GAC(0.075).The proportion of GGC/GGC(70.9%), GGC/GAC(27.3%),GAC/GAC(1.8%) were significantly different from that in the normal children,and the frequency of GGC/GAC mutation and allele GAC(0.155) increased significantly(P＜0.05) compared with the normal children.The frequency of allele GAC and mutant heterozygous GGC/GAC at codon 54 in children with RRTI was significantly higher than that in the control group(X~2=4.47-5.64,P＜0.05); Mutant code 57 in the two groups were not detected.⑤The children with MBL structural gene code 54 genotype GGC/GGC,GGC/GAC,GAC/GAC had corresponding high,medium,and low serum MBL levels respectively,and there was significantly difference(t=2.49,P＜0.05;t=4.36,P＜0.001) between them.The proportionof wild-type GGC/GGC in code 54 in the groups with low serum MBL level in the RRTI group was 16%and the mutant-type GGC/GAC in the same population was 76%,which was significantly higher than that in the group with normal MBL level(x~2=49.12,P＜0.001).Conclusion①The level of serum MBL in preterm infants was significantly lower than that of full-term infants group,the level of serum MBL in healthy children of all ages is relatively stable.There were no significant difference among different gender and different age.②The level of serum MBL in RRTI was significantly lower than the healthy group;The rate of low serum MBL level in the children with RRTI was higher than that in the healthy group.MBL defect was an important reason of RRTI in children.③The polymorphism of genotypes result from mutations on the code 54 leaded to relevant serum MBL level,in which GGC was associated with high MBL level and GAC was associated with low MBL level.Allele GAC which was related to low serum MBL was the risk factor of RRTI in children.
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