ALTERATIONS IN PERIPHERAL-BLOOD LEUKOCYTE DISTRIBUTION IN RESPONSE TO LOCAL INFLAMMATORY STIMULI IN RAT

Changes in peripheral blood leukocyte distribution were monitored following s.c. injections of turpentine and s.c. and intrapleural injections of dextran. The responses in all 3 groups were similar; marked increases in total counts occurred at 6 h, due largely to significant increases in neutrophil counts. Increases in lymphocyte counts also occurred and were more marked in the dextran-treated animals. By 12 h total counts fell, due to drops in both neutrophil and lymphocyte counts. In both dextran groups neutrophil counts rose again between 24 and 72 h, but in the turpentine group the fall persisted until 96 h before counts reached a 2nd peak at 14 days. In all groups lymphocytes showed an increase again at 18-72 h. The rise in neutrophil counts observed 6 h after the injection of turpentine was due principally to premature release of neutrophils from the bone marrow maturation compartment. Depletion of this compartment resulted in a drop in numbers of circulating neutrophils between 6 and 12 h, in spite of the continued release of progressively less mature cells. The recovery in neutrophil counts between 72 and 96 h was thought to be the expression of an increase in the rate of stem cell division. The continued rise to a 2nd peak at 7 days probably resulted from increased marrow cellularity. The fluctuations in peripheral blood leukocyte counts may influence the initial colonization of the local inflammatory lesion. The increase in neutrophil counts at 6 h corresponded with the time of maximum neutrophil emigration reported by other workers, and the fall in counts at 12 h corresponds with the time of decreased neutrophil emigration.