Localization and functional characterization of pulmonary bovine odorant-binding protein.
Bovine odorant-binding protein (OBP) may function in olfaction and defense against oxidative injury, but its role in inflammation and defense against bacterial infection has not been investigated. Expression of OBP was discovered in the bovine lung and found to undergo changes in abundance during glucocorticoid administration and stress. OBP was localized to nasal, tracheal, and bronchial mucosal glands with immunohistochemistry, with faint expression in airway surface epithelium and none in bronchioles or alveoli. Two isoforms of OBP were identified, appearing to be differentially regulated during lipopolysaccharide-induced pulmonary inflammation, but differences between these isoforms were not revealed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Functional studies showed no effect of OBP on in vitro growth of Escherichia coli or Mannheimia haemolytica under iron-replete or iron-depleted conditions, nor did OBP opsonize bacteria for an enhanced neutrophil oxidative burst. However, OBP did reduce the ability of supernatants from lipopolysaccharide-stimulated macrophages to induce neutrophil chemotaxis. These findings indicate that OBP may inhibit neutrophil recruitment by inflammatory mediators, and they suggest an ability to bind macrophage-derived inflammatory mediators within the airways.