Leukocyte rolling: a prominent feature of venules in intact skin of anesthetized hairless mice.

Leukocyte (white blood cell; WBC) rolling in postcapillary venules is a frequently reported phenomenon in the microvasculature of experimental preparations. In most reports where this phenomenon has been systematically studied the confounding effects of various procedures associated with tissue preparation have been present. Thus there is sparse information on the extent of WBC rolling under fairly normal conditions. Here observations and features of this phenomenon in venules in the intact skin microvasculature of the homozygous hairless mouse ear are described. One venule in each of 10 mice was observed and continuously video recorded for 90 min. The parameters determined (mean +/- SD) were diameter, 15.9 +/- 3.1 microns; red blood cell velocity, 359 +/- 227 micron/s; flux of rolling WBCs, 3.2 +/- 2.6/min; velocity of rolling WBCs, 9.6 +/- 1.1 micron/s; systemic WBC count (CWBC), 3,220 +/- 1,072/microliters; and total WBC flux, estimated as the product of CWBC and calculated venule blood flow, 8.5 +/- 3.0/min. Overall, 44.8 +/- 13.8% of the total WBC flux exhibited rolling with a velocity that was 3.6 +/- 2.9% of the red blood cell velocity. During the total 15-h combined observation time, no WBCs were seen to be adherent. These findings establish that in small venules of normal skin, WBC rolling is common, since on the average nearly one of two WBCs delivered to the venule exhibits rolling. Furthermore, because the translational rolling speed is very low, they contribute to the marginated pool, which, according to the present data, might be better termed the "rolling" pool.