Genetic variation in bactericidal/permeability-increasing protein influences the risk of developing rapid airflow decline after hematopoietic cell transplantation

Abstract

Innate immunity is involved in the biology of graft versus host disease and common airway diseases. We screened 15 genes in this pathway using a linkage disequilibrium-based approach to identify potential candidate genes that may be involved in the development of airflow obstruction after hematopoietic cell transplantation. Sixty-nine single-nucleotide polymorphisms were selected for assessment in a discovery cohort (n = 363). Significant associations were validated in a validation cohort (n = 209). Expression of the candidate gene was demonstrated by detecting gene transcript and protein in malignant and normal small airway epithelial cells. In the discovery cohort, 133 patients developed significant airflow decline. Four patient and donor bactericidal/permeability-increasing (BPI) haplotypes were associated with a 2-fold to 3-fold increased risk of developing significant airflow decline (P values, .004-.038). This association was confirmed in the validation cohort, which had 66 patients with significant airflow decline, with 9 significant haplotypes (P values, .013-.043). BPI gene transcript and protein were detected in airway epithelial cells. These results suggest mutations in the BPI gene significantly influence the risk of developing rapid airflow decline after hematopoietic cell transplantation and may represent a novel therapeutic target for this form of airway disease.

Figure 1.

Human airway epithelial cells express the BPI gene and produce the BPI protein. (A) This panel shows that A549 human lung epithelial cells and human SAECs constitutively express the BPI gene. Buffy coat from whole blood stimulated with lipopolysaccharide served as a positive control. Total RNA was isolated, and BPI mRNA was examined by RT-PCR. 18S ribosomal RNA was used as a loading control. (B) This panel shows that by flow cytometric analysis, A549 cells, SAECs, and neutrophils all stained positively for BPI protein. Permeabilized cells were stained with monoclonal antibody to BPI, murine IgG control, and/or murine anti-human anticytokeratin monoclonal antibody, followed by FITC-conjugated goat antimouse antibody. Fluorescence intensity was well above background staining with control IgG.