The fate of blood granulocytes.

The present study was undertaken to determine whether neutrophilic granulocytes leave the vascular bed and enter body tissues, particularly the lung, in pathogen-free mice under normal steady state conditions and also under inflammatory stress. Tissues from normal mice and from mice with granulocytosis-producing tumor were processed for electron microscopic studies. Neutrophils have not been seen outside the capillary or in the pulmonary epithelium in alveoli under normal steady state or in mice with leukocyte counts of 300,000/mm3 in which capillaries were replete with neutrophils. Emigration of neutrophils outside the capillaries was observed under inflammatory conditions. Granulocytes were also observed to be concentrated for destruction in the spleen, perhaps the major site for removal of granulocytes. In the pathogen-free mice granulocytes did not appear to leave blood vessels and enter tissues.