THE ROLE OF CYTOSKELETAL PROTEINS IN NEUTROPHIL EMIGRATION DURING PNEUMONIA IN RABBITS

The cytoskeletal proteins, actin and tubulin, are critical in modulati ng many aspects of the structural, mechanical, and biochemical propert ies of cells. This study determined if rearrangements of microtubules or filamentous actin were necessary for neutrophil margination within the pulmonary microvasculature or emigration into the alveolar spaces in response to Streptococcus pneumoniae. Microtubule assembly was inhi bited using colchicine, and F-actin depolymerization was inhabited usi ng phalloidin. Anesthetized rabbits received an intrabronchial instill ation of S. pneumoniae either after intravenous pretreatment with colc hicine (1 mg/kg every 2 h) or combined with TRITC-phalloidin (2 mu M i n instillate). Four hours later, the lungs were fixed and removed. The results show that the intravenous injection of colchicine caused a ra pid decrease in circulating neutrophil counts, most likely caused by s equestration within the pulmonary microvasculature, that gradually rec overed. In the pneumonic region, colchicine inhibited neutrophil emigr ation by 74 +/- 5%, but it did not prevent the stimulus-induced increa se in margination. Phalloidin inhibited neutrophil emigration by 83 +/ - 4%. These studies suggested that microtubule reassembly occurs durin g neutrophil transit through the normal pulmonary microvasculature and that it is required for migration but not sequestration during pneumo nia. Rearrangement of actin filaments in lung cells but not neutrophil s are required for neutrophil emigration induced by S. pneumoniae.