Effect of Aerosolized Escherichia coli and Staphylococcus aureus on Iron and Iron-Binding Proteins in Lung Lavage Fluid

Iron-binding proteins have antibacterial activity; they have been identified in lung secretions, but their role in pulmonary antibacterial defenses is unclear. Murine lactoferrin and murine transferrin were used to generate polyclonal antiserum to lactoferrin and to transferrin, and the specificity of both antisera was shown by western blot. Mice were exposed to either aerosolized Escherichia coli or Staphylococcus aureus; they were killed 1, 4, 24, or 48 hr later; and their lungs were lavaged. Wemeasured the levels of transferrin, lactoferrin, and albumin and did a cell count for the lavage fluid. The predominant ironbinding protein in resting animals wastransferrin. Aerosolized E. coli caused a brisk PMNL response in the lungs that was associated with a major increase in the levels of lactoferrin. Challenge with S. aureus was associated with a moderate increase in the number of macrophages and a moderate decrease in the levels of transferrin and iron but no change in the levels of lactoferrin. The levels of iron-binding protein can vary according to the type of inflammatory response.