Effects of products from inflammatory pulmonary neutrophils on alveolar macrophage chemotaxis, spreading, and thymidine incorporation

Since macrophages and neutrophils are found together in the alveolar region of the lung during alveolar inflammation, we assessed whether neutrophil products could influence three key functions of alveolar macrophages: chemotaxis, spreading, and thymidine incorporation. Neutrophils were obtained from the lungs of rats treated by intratracheal instillation of heat-killed Corynebacterium parvum and cultured overnight, alone or in the presence of zymosan, PMA, an inert particulate (titanium dioxide), or a toxic dust, (quartz). Supernatants were collected from these cells and a lysate, obtained by freeze-thawing neutrophils, was also used. Neutrophil supernatants caused a slight reduction in chemotaxis and a significant loss of ability to spread on glass which varied depending on the in vitro treatment of the neutrophils. In addition neutrophil supernatants also had a substantial effect in stimulating uptake of thymidine which was, once again, very dependent on the treatment of the neutrophils during preparation of the supernatants, with unstimulated and TiO₂-treated neutrophils producing maximum stimulation. The increases in thymidine uptake were not matched by increased proliferation, suggesting that another signal may be necessary for expansion of alveolar macrophage numbers during alveolar inflammation.