Leukocyte and platelet margination within microvasculature of rabbit lungs.

These studies compare the behavior of radiolabeled neutrophils, monocytes, lymphocytes, and platelets during their first pass through the pulmonary circulation after a central venous injection and their distribution within the circulation 10 min later. Their first pass through the pulmonary circulation was compared with erythrocytes (RBCs) using the indicator-dilution technique, and their recovery within the circulation of the lung and other organs was determined at 10 min by counting the radioisotopes in each organ. The extraction of each cell relative to RBCs during the first pass through the lung correlated with cell size in that the neutrophils (volume 107-140 fl) showed 97.6 +/- 0.6% extraction, monocytes (volume 80-105 fl) showed 91.4 +/- 1.7% extraction, lymphocytes (volume 36-75 fl) showed 80.1 +/- 4.4% extraction, and platelets (volume 4-7 fl) showed 33.1 +/- 3.9% extraction. After 10 min of circulation, the proportion of injected cells remaining in the lung was similar for neutrophils and monocytes (27.4 +/- 1.8 vs. 31.4 +/- 1.6%) but lower for lymphocytes (18.6 +/- 2.9%) and platelets (3.1 +/- 0.5%). All of the leukocytes were found to have a substantial marginated pool within the lung, whereas the platelets did not. The exchange between the circulating and marginated pools of leukocytes in the lung was related to blood velocity, with the least retention occurring in lung regions with shortest RBC transit times. We conclude that cell size is a major factor determining the time that cells will be delayed by the pulmonary microvasculature.(ABSTRACT TRUNCATED AT 250 WORDS)