Alterations in peripheral blood leucocyte distribution in response to local inflammatory stimuli in the rat.

Changes in peripheral blood leucocyte distribution were monitored following subcutaneous injections of turpentine and subcutaneous and intrapleural injections of dextran. The responses in all three groups were similar; marked increases in total counts occurred at 6 hr, 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 hr, total counts fell, due to drops in both neutrophil and lymphocyte counts. In both dextran groups, neutrophil counts rose again between 24 and 72 hr, but in the turpentine group the fall persisted until 96 hr before counts reached a second peak at 14 days. In all groups lymphocytes showed an increase again at 18-72 hr. The rise in neutrophil counts observed 6 hr after the injection of turpentine was shown to be 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 hr, in spite of the continued release of progressively less mature cells. The recovery in neutrophil counts between 72 and 96 hr was thought to be the expression of an increase in the rate of stem cell division. The continued rise to a second peak at 7 days probably resulted from increased marrow cellularity. It is suggested that the fluctuations in peripheral blood leucocyte counts may influence the initial colonisation of the local inflammatory lesion. The increase in neutrophil counts at 6 hr corresponds with the time of maximum neutrophil emigration reported by other workers and the fall in counts at 12 hr corresponds with the time of decreased neutrophil emigration.