Neutrophil kinetics in rabbits during infusion of zymosan-activated plasma

Complement activation in vivo produces neutropenia and pulmonary sequestration of neutrophils (PMNs) whereas in vitro activation increases PMN adherence and decreases PMN deformability. The present study examined PMN kinetics in vivo to determine if this sequestration was specific to the lung. Venous or arterial injections of radiolabeled PMNs were given to animals receiving infusions of zymosan-activated plasma (ZAP) or saline, and the PMN distribution was evaluated 10 min later. In control animals, the relative size of the marginated and circulating PMN pools was similar after venous or arterial injection and regional PMN retention increased as blood velocity slowed. ZAP infusion produced threefold increases in PMNs within pulmonary capillaries after venous injection and PMN retention was independent of blood velocity. After arterial injection, ZAP infusion produced PMN sequestration in all organs. Rigid (glutaraldehyde-fixed) PMNs injected into control rabbits showed increased lung recoveries similar to those of fresh PMNs injected into ZAP-treated rabbits. We conclude that activation of the complement system causes PMN sequestration in both the pulmonary and the systemic microvasculature and that the decrease in PMN deformability that occurs with activation of the PMN may be important in the genesis of PMN sequestration.