Leukocyte-endothelial cell interactions in lung capillaries. (A,B) Images show rhodamine-6G–labeled leukocytes (white dots) in venular capillaries margins of which are outlined (white lines). At hematocrit of 20%, whereas few leukocytes adhere to the venular endothelium under baseline conditions (top left), leukocyte attachment to the endothelium is greater after 30 minutes of hypoxia (top right). By contrast, at hematocrit of 0% hypoxia causes no leukocyte adhesion (bottom right). (C-K) Group data show leukocyte rolling (WBCrol/min) and sticking (WBCstick/min) rates and RBC velocity (k) for normoxia (baseline) and after 30 minutes of hypoxia (hypoxia) under the indicated conditions. Vessels were perfused at 20% hematocrit except as indicated. anti–P-sel indicates P-selectin mAb. #P < .05 vs baseline (panels C,D,I,J); *P < .05 versus WT-RBC in WT-lung (1st bar, panels G,H).