[Association between genetic polymorphism of erythrocyte CR1 and the susceptibility of idiopathic pulmonary fibrosis].

OBJECTIVE: To explore the association between the erythrocyte CR1 genomic density polymorphism, A3650G site polymorphism and the susceptibility of idiopathic pulmonary fibrosis (IPF); and to investigate the correlation between the HindIII density polymorphism of CR1 gene and the quantitative levels of E-CR1 in IPF patients.

METHODS: Blood samples from IPF patients (n = 64) and ethnically matched healthy controls (n = 54) were taken from a population-based case-control association study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed to identify the genotype of the HindIII restriction fragment length polymorphism of CR1 gene and SNP A3650G in two groups. Quantitative expression of CR1 on RBC membrane surface was detected by flow cytometry.

RESULTS: The genotype frequencies of HH, HL and LL were 32.8% (21/64), 46.9% (30/64) and 20.3% (13/64) respectively in the IPF group, and 72.2% (39/54), 25.9% (14/54) and 1.9% (1/54) respectively in the controls. The distribution of genotype between the two groups was significantly different (χ(2) = 15.516, P < 0.05). HL + LL genotype for the HindIII polymorphism was more common in patients with IPF compared to the controls with an OR = 5.32 (χ(2) = 18.20, P < 0.05). Compared the allele frequency of A3650G sites in the IPF group with that in the control group, there was no difference from distribution in the two groups (χ(2) = 1.094, P > 0.05). The mean CR1/E numbers observed in the IPF patients was 13.46 ± 3.86, and the mean CR1/E in normal individuals was 24.33 ± 3.84 (t = 15.288, P < 0.05 vs IPF group). The levels of E-CR1 in both IPF patients and healthy controls HH genotype for E-CR1 HindIII-RFLP were significantly higher than HL genotype for E-CR1 HindIII-RFLP (t = 9.973, P < 0.05), and the levels of E-CR1 in both groups HL genotype for E-CR1 HindIII-RFLP were significantly higher than LL genotype for E-CR1 HindIII-RFLP (t = 9.973, P < 0.05). The levels of HH, HL and LL genotypes for E-CR1 HindIII-RFLP in the IPF group were significantly lower than those in the control group, respectively (P < 0.05, on average).

CONCLUSION: The quantitative levels of CR1 on erythrocyte membrane was not only determined by the genetic background of E-CR1 HindIII-RFLP but also by the acquired predisposition. HL and LL genotypes of CR1 gene may be associated with IPF, and as a result individuals carrying the L allele might be a susceptible population for IPF.