Leukocyte recruitment in the airways: An intravital microscopic study of rat tracheal microcirculation

Because of its relative inaccessibility, inflammatory cell extravasation within the airway circulation in vivo has been difficult to investigate in real time. A new method has been established using intravital microscopy in the anesthetized rat to visualize leukocytes in superficial postcapillary venules of the trachea. This technique has been validated using local superfusion of lipopolysaccharide (LPS) and Nformyl-methionyl-leucyl-phenylalanine (FMLP). Basal leukocyte rolling velocity (55.4 ± 9.3 μm/s) and adhesion (1.4 ± 0.3 cells/100 μm) were monitored in postcapillary venules (33.9 ± 1.3 μm diameter). At all time points up to 90 min, these parameters were unaltered in control rats (n = 7). In contrast, vessels exposed to 1 μg/ml of LPS (n = 6) exhibited a 57% reduction in leukocyte rolling velocity and an increase in the number of adherent cells (4.7 ± 1 cells/100 μm, P < 0.05). Superfusion with 0.1 μM of FMLP (n = 6) also resulted in a 45% reduction in rolling velocity and an increase in adherent cells (4 ± 0.7 cells/100 μm, P < 0.05). Histological evaluation confirmed local stimulus-induced leukocyte extravasation. These results demonstrate leukocyte recruitment in the airway microvasculature and provide an important new method to study airway inflammation in real time.