-ABSTRACT-
Genetic Effect of MBL2 Polymorphisms
in Patients with Diisocyanate-induced Occupational Asthma
Background and Objective: Diisocyanate (DI) is the most common cause of occupational asthma (OA) in Korea. Although various mechanisms were involved in the pathogenesis of DI-OA, oxidative stress has been suggested as a potential mechanism, which leads to the formation of a complement-activating mannose-binding lectin (MBL) ligand on human endothelial cells. MBL initiates the lectin complement activation pathway following oxidative stress and generate complement cascade, which is involved in chronic airway inflammation.
Materials and Methods: To demonstrate genetic association of MBL2 polymorphisms in DI-OA, 99 patients with DI-OA, 99 asymptomatic exposed controls (AEC) and 144 unexposed normal controls were enrolled. Three polymorphisms (-554 G>C, -431 A>C and -225 G>C) in the MBL2 promoter were genotyped by TaqMan allelic discrimination assays using TaqMan probes. The serum MBL levels were detected using enzyme-linked immunosorbent assay (ELISA). The functional variabilities of the promoter polymorphisms were analyzed by luciferase reporter assay and electrophoretic mobility shift assay (EMSA). Result: Significantly higher frequency of the AA genotype at -431 A>C (P=0.016) and higher frequency of haplotype (ht) 2 [CAG] were noted in the DI-OA group compared to AEC group (P=0.044). DI-OA patients carrying the GG genotype at -225 G>C, and ht2 [CAG] had significantly lower PC20 methacholine levels (P=0.030, and P<0.001, respectively) than non-carriers. Serum MBL levels were significantly higher in DI-exposed subjects (including both DI-OA and AEC) carrying the GG genotype of -554 G>C and/or -225 G>C than those of other genotypes (P=0.004 and P=0.010, respectively). The DI-OA exposed subjects carrying ht1 [GAG] showed higher serum MBL levels (P=0.004), while the subjects carrying ht3 [CAC] had significantly lower serum MBL levels (P=0.020) than those with others. The luciferase activity was enhanced significantly in the construct containing -554G compared to the -554C in human hepatocarcinoma cell (Hep3B) (P=0.002). EMSA showed that a -554G probe produced a specific shifted band compared to a -554C probe. Conclusion: These findings suggest that MBL2 ht2 [CAG] was significantly associated with the phenotype of DI-OA and MBL2 polymorphism at -554 G>C affects serum MBL levels via increased promoter activity in DI-exposed subjects.
Key words: Genetic polymorphism, isocyanate, MBL2, occupational asthma
