Leukocytic responses to the intrapleural deposition of particles, particle‐cell associations, and the clearance of particles from the pleural space compartment

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Abstract
Polystyrene microspheres (2.02 μm diameter) were instilled in the pleural space compartment (PSC) of the Fischer 344 rat. Rats that were administered carrier vehicle only, and untreated rats served as controls. On d 1, 6, 14, and 28 following the instillations, the pleural free cells were harvested by pleural lavage and the major cell phenotypes retrieved were quantitated to determine how the pleural free cell population was altered by the particles. Concurrent with these studies, quantitative analyses were performed to determine the numbers of particles lavaged from the pleural space at the above sacrifice times, and these particle retention data were used to estimate particle translocation rates from the PSC. Deposition of the particles in the PSC brought about an early recruitment of polymorphonuclear leukocytes (PMN) and an enlargement in the size of the pleural mononuclear phagocyte (PMP) population. PMN numbers substantially decreased by d 6, but continued to remain elevated over the course of the study. The early increase in PMP appeared to subside by d 6, but again increased thereafter. Other notable changes were decreases in the size of the pleural eosinophil population at later times after particle deposition, and an approximate 200‐fold increase in lymphocytes by d 28. The particles were cleared from the PSC with a biphasic pattern. The most rapid phase, which accounted for the clearance of ≥ 80% of the particles, had a t1/2 = 0.3 d and the slower component had a t1/2 = 6 d. Most of the particles were translocated from the PSC to the retrosternal, caudal mediastinal tissue. The slower phase of particle clearance appeared to be macrophage‐mediated, suggesting the t1/2 for macrophages in the PSC is also ∼6 d.