Activation-associated changes in blood and bone marrow neutrophils

Accelerated granulocytopoiesis and polymorphonuclear leukocyte (PMN) activation via the complement system are important events in the inflammatory response. This study tests the hypothesis that PMN of the peripheral blood and the bone marrow behave differently when stimulated with zymosan-activated plasma (ZAP). PMN were treated with ZAP and processed to determine the content and distribution of F-actin, the expression of CD18-integrins, and the cell area/shape with the use of a combination of flow cytometry, fluorescence, and light microscopy. The results show that untreated bone marrow PMN display similar F-actin content and cell area but express less CD18 than peripheral blood PMN. ZAP-activated peripheral blood PMN show a marked increase in the F-actin content, CD18 expression, cell area, and length. Highly elongated PMN develop a polar shape in which microfilaments are redistributed in cell protrusions and CD18 is located in the uropod and the lamellipodium. In comparison, activated bone marrow PMN show a lower and more transient increase in the F-actin content, express less CD18, show a reduced increase in the cell area, and display reduced polarity and microfilament redistribution. We conclude that bone marrow PMN show lower complement-activation response than peripheral blood PMN and suggest that the lower expression of surface membrane integrins and related cytoskeletal filaments may account for their reduced ability to develop the polar shape required for diapedesis and migration.