Rapid leukocyte accumulation by "spontaneous" rolling and adhesion in the exteriorized rabbit mesentery

Leukocyte concentration in venules of exteriorized rabbit mesentery was calculated from intravascular white blood cell counts and venular length and diameter measured in histological whole mount preparations. Immediately after exteriorization, the mean venular leukocyte concentration (MVLC) was found to be slightly below systemic leukocyte concentration. One to five minutes later, MVLC was 7 times, and 30 minutes later, 20 times above systemic values. The concentrations of both polymorphonuclear and mononuclear leukocytes (PMNs, MNs) increased, but PMNs accumulated faster and in higher numbers (8 fold vs. 4 fold at 5 minutes, 24 vs. 14 fold at 30 minutes, respectively). The observed leukocyte accumulation in mesentery venules was found to be due to adherence of leukocytes which is absent in normal tissue, but was rapidly induced by exteriorization. Intravital microscopy revealed that many leukocytes were rolling along the venular endothelium. Dextran sulfate, a potent inhibitor of leukocyte rolling largely prevented leukocyte accumulation after exteriorization (twice systemic vs. 6 times in control). A monoclonal antibody (60.3) blocking CD18 of the leukocyte adhesion complex attenuated leukocyte accumulation to a lesser extent (3.5 times systemic). The data indicate that leukocyte rolling accounts for the major part of "spontaneous" leukocyte accumulation in the exteriorized mesentery.