Enzyme release and morphological changes in leukocytes induced by mechanical trauma.

Polymorphonuclear (PMN) leukocytes exposed to mechanical trauma in vitro will release enzymes both from azurophilic and specific granules at shear stress levels of between 75 and 150 dyn/cm2 for 10 min. In addition, at these shear stresses the leukocyte count in whole blood decreased only slightly and the number of ruptured leukocytes on Wright-stained blood films increased significantly. At higher shear stresses, enzyme release and leukocyte damage increased monotonically. Transmission electron microscopy evaluation of sheared PMNs revealed that remaining intact cells had minor morphological changes at stresses of 150 dyn/cm2. They were characterized by clublike cytoplasmic potrusions, spherical shape, and a circumferential distribution of cytoplasmic granules. At higher shear stresses (600 dyn/cm2) cell destruction was marked. Intact PMNs contained fewer cytoplasmic granules, a large number of vacuoles, and condensed nuclear chromatin. These studies show that PMN morphology and function are at least as sensitive to mechanical trauma as similar platelet alterations seen in other studies.

Mechanical trauma in leukocytes.

Mechanical and surface traumas in cardiopulmonary bypass circuits alter the function and morphology of human leukocytes. The effect of controlled in vitro shear stess (0 to 2,000 dynes/cm2, 2 to 10 min, 37 degrees C) on electronic cell count, morphology, adhesiveness, and phosphatase cytochemical staining was studied on whole blood from normal donors. Electronic cell counts droppped significantly after shear stress exposure (25% at 600 dynes/cm2 for 10 min). The frequency of disrupted leukocytes in blood smears increased with shear stress above 150 dynes/cm2, and aggregates of the disrupted cells appeared after exposure to higher shear stresses (450 dynes/cm2, 10 min). Cytochemical staining of the alkaline phosphatase in the granules of intact neutrophils was significantly reduced by the application of shear stress (150 dynes/cm2 for 10 min, or greater), but staining of acid phosphatase-containing granules was almost unaffected. Increased cell retention in columns of nylon fibers suggests that increased leukocyte adhesiveness results from exposure to shear stress. Thus exposure to shear stress may alter or disrupt leukocyte morphology and function at values somewhat lower than the 1,500 dynes/cm2 for 2 min which is required to hemolyze erythrocytes.