Lung deformation and macrophage displacement in smoke-exposed and normal mice (Mus musculus) following different fixation procedures.

Lung deformation (shrinkage or inflation) and displacement of pulmonary parenchymal macrophages were evaluated after immersion fixation, intratracheal instillation of fixative and lung lavage followed by intratracheal fixative instillation in cigarette smoke-exposed, sham-treated and control pallid male mice. Lung volume displacement and lung section and alveolar area analysis revealed that degree of deformation was uniform in lungs from all treatment groups fixed by immersion but not by instillation of fixative and fixative instillation following lavage. In situ pulmonary parenchymal macrophage number per lung section area of fixative-instilled lungs and lavaged lungs followed by fixative instillation was significantly greater than in those following immersion fixation in all corresponding treatment groups. A paucity of macrophages was noted in airways of fixative-instilled and lavaged followed by instillation of fixative lungs. Pulmonary macrophages were uniformly distributed throughout lung parenchyma following immersion fixation, while in fixative-instilled and lavaged prior to instillation of fixative lungs these cells tended to be concentrated in alveoli near terminal bronchioles. Lavage procedures removed an unknown portion of lung macrophages and appeared to ineffectively sample the pulmonary parenchymal macrophage population. Intratracheal instillation of fixative with or without prior lavage apparently alters the distribution of pulmonary macrophages by displacing airway phagocytes into the alveoli. Data reported suggest that fractional estimates of in situ lung parenchymal macrophage population can be obtained by counting the number of these cells per area of tissue from lungs fixed by immersion.