Coordinated influence of β-defensins on innate immunity against bacterial infection of the airway (112.12)

Abstract β-defensins act as antimicrobial agents and as immunomodulators. Human β-defensin (BD) peptides 1, 2 and 3 are differentially modulated in primary tracheal epithelial cells (TEC) by viruses, bacteria, and proinflammatory cytokines. We hypothesized that hBD-1 and virulence factors would influence induction of hBD-2 and hBD-3 during lung bacterial infections. Since BD genes exist in close proximity on chromosome 8, making it impossible to delete more than one BD gene, a model was devised to study their coordination. Since mouse orthologs exist, (hBD-1=mBD-1; hBD-2=mBD-3; hBD-3=mBD14), we used mBD-1(-/-) (KO) mice and the inhibitory capability of the type III secretion system of Bordetella bronchiseptica on NF-κB to study effects of mBD-1 deletion on mBD-3 gene expression using wild-type RB50 and mutant WD3 strains lacking this system. In C57BL/6 wild-type (WT) mice, mBD-3, mBD-14 and kerotinocyte-derived chemokine (KC) mRNA levels were suppressed by RB50 compared with WD3 induction in lung 24 hr after infection, whereas mBD-1 levels were unaffected. Deletion of mBD-1 significantly blunted WD3 induction of mBD-3 and mBD-14, but not KC. Bacteria numbers increased, along with decreased neutrophils in the trachea, when KO mice were infected with RB50 compared with WT mice. In TEC, WD3 induced mBD-3 in WT but not in KO mice, yet with cultured KO TEC, mBD-14 and KC were unaffected. The results illustrate the coordination of BD in TEC and in lung to influence bacterial infection.