- Top of page
- Material and methods
Background: There has been no study for evaluating the associations of human leukocyte antigen (HLA) class I and II alleles with toluene diisocyanate (TDI)-induced asthma in an Asian population.
Objective: The aim of this study was to investigate a susceptible or protective marker of HLA class I and II alleles in TDI-induced asthma.
Methods: Fifty-five patients with TDI-induced asthma patients (group I) showing positive responses on TDI bronchoprovocation test, 47 asymptomatic exposed subjects (group II) and 95 unexposed healthy nonatopic controls (group III) were enrolled in our study. HLA class I and II genotyping was done by the direct DNA sequencing method.
Results: The allelic frequency of C*09 (15.5%) was significantly higher in group I than in group III (6.8%, P = 0.019), but this statistical significance disappeared after correction was made for multiple comparisons. On two-locus and three-locus haplotype analysis, the allelic frequency of HLA DRB1*15-DPB1*05 in group I (10.6%) was significantly higher than that of group II (0%, P = 0.001) and group III (2.5%, P = 0.003). The allelic frequencies of HLA A*02-DRB1*15, A*02-DQB1*06, B*62-C*09 and A*02-DRB1*15-DQB1*06 were significantly higher in group I (8.5%, 10.3%, 8.2% and 6.8%, respectively) than those allelic frequencies of group III (1.3%, P = 0.002; 1.6%, P = 0.001; 0.6%, P < 0.0001; 0%, P < 0.0001, respectively). The allelic frequencies of HLA DQB1*06-DPB1*05 and DRB1*15-DQB1*06-DPB1*05 were significantly higher in group I (16.0% and 10.5%) than those in group II (2.5%, P = 0.001; 0%, P = 0.001), while the frequencies of DRB1*09-DPB1*05 and DRB1*09-DQB1*0303-DPB1*05 were significantly lower in group I (0% and 0%) than those of group II (7.4%, P = 0.004; 7.5%, P = 0.004). These differences remained statistically significant even after the correction for multiple comparisons.
Conclusions: The HLA haplotype DRB1*15-DPB1*05 can be a susceptibility gene marker for the development of TDI-induced asthma among the exposed workers in the Korean population.
Toluene diisocyanates (TDI) are one of the most commonly identified causes of occupational asthma in far east-Asia (1). Previous studies have demonstrated that CD4+ and CD8+ T cells, as well as eosinophils and mast cells, could be involved in the pathogenic mechanism of TDI-induced asthma (2, 3). Regarding the genetic mechanisms, there has been a study demonstrating that the human leukocyte antigen (HLA) DQB1*0503 and DQB1*0201-0301 haplotypes are susceptibility gene markers for TDI-induced asthma in an Italian population (4, 5), while no significant associations were found in another studies, based on European populations, for the HLA class II and HLA class I alleles (6, 7).
In this study, we analyzed both the HLA class I and II alleles in TDI-induced Korean asthma patients compared with two Korean control groups, the asymptomatic exposed control subjects and unexposed healthy control subjects in order to investigate the susceptible or protective markers. In addition, two-locus and three-locus haplotype analysis was also performed.
- Top of page
- Material and methods
The pathogenic mechanism of TDI-induced asthma is currently not completely understood. Although there has been a few studies with Caucasian population on the genetic mechanism of TDI-induced asthma, the results are still controversial. The previous European study performed on 142 patients with TDI-induced asthma and 50 asymptomatic exposed controls demonstrated that HLA class I alleles were not significantly associated with the phenotype of TDI-induced asthma (7). Other studies have used high resolution technique to analyze HLA class II alleles for comparing TDI-induced asthma subjects and asymptomatic exposed controls. They have demonstrated that one HLA class II allele (DQB1*0503) and one haplotype (DQB1* 0201-0301) were significantly associated with the phenotype of TDI-induced asthma (4, 5), yet based on a German population, no association was found for the HLA class II allele (6). In this study, when we analyzed high resolution HLA markers: two class I alleles (C*0303, C*0602) and three class II alleles (DRB1*0403, DRB1*1501, DQB1* 0602) seemed to be possible susceptibility gene markers for the development of TDI-induced asthma, but their statistical significances disappeared after correction was made for multiple comparisons. Moreover, based on high resolution data (data was not shown), significant alleles were not found on the two-locus or three-locus haplotype analysis. Therefore, we adopted the low resolution data on the HLA class I and II alleles for this study, and we extended the two and three-locus haplotype analysis to include the HLA class I and II alleles. Among all the HLA class I and II alleles, no single allele had any significant association with the TDI-induced asthma phenotype in our Korean study population, and this may have been because the number of study subjects was not large enough to present a strong single gene marker for this phenotype. Further investigation with a larger group of subjects will be needed to identify a single HLA allele for this condition.
The value of this study was that we analyzed both HLA class I and II alleles in all the study subjects; secondly, we enrolled two control groups: the asymptomatic exposed subjects and unexposed healthy nonatopic control subjects; thirdly, haplotype analysis was used to try to identify susceptible and protective gene markers. Although significant associations were not found on the single allele analysis, two and three locus haplotype analysis demonstrated several significant alleles as a potential susceptible or protective markers. Among them, we suggest that the HLA haplotype DRB1*15-DPB1*05 may be a useful marker for predicting the development of TDI-induced asthma in the Korean population.
Future studies will be needed to evaluate any HLA gene markers for their association with such immunologic markers as serum specific IgE and IgG antibodies to the TDI-human serum albumin conjugate in the exposed subjects, and how these gene markers could be involved in the pathogenic mechanisms of asthma.