Effect of proteins and lipids of the alveolar lining layer on particle binding and phagocytosis

The initial interactions between macrophages and particles on alveolar surfaces could be significant events in the pathogenesis of certain lung diseases, since these cells are known to secrete a variety of inflammatory mediators and growth factors. It has been determined that the protein and lipid fractions of the extracellular alveolar lining layer (ALL) affect alveolar macrophage morphology and function in vitro and that these fractions can block the binding of iron and glass spheres to macrophage membranes. Protein-rich and lipid-rich fractions were prepared for treatment of alveolar macrophages in vitro. The 'normal' (i.e. non-concentrated) lavage diluted by saline caused no measurable changes in macrophage morphology or function. In contrast, concentrated lavage, as well as the protein and lipid fractions, caused loss of cell viability and blocked the binding of positively and negatively charged particles to macrophage membranes. The blocking effect could be reversed when the cells were pretreated with the lavage fraction and then washed. Blocking of binding could not be reversed when the particles were pretreated. The binding of particles to macrophage membranes appears to be mediated through an interaction between the particles and the ALL.