Characterization of nonmotile neutrophil subpopulations in neonates and adults.

Previous studies have demonstrated that polymorphonuclear leukocytes (PMN) are not a homogeneous population of cells but differ significantly in their structure and function. PMN move at varying rates, and a fraction estimated from 20 to 70% do not move at all in response to chemotactic stimuli. To characterize this PMN subpopulation better, we studied PMN motility in neonates and adults using a polycarbonate micropore filter chemotactic assay and the 31D8 MAb. Most PMN strongly bind 31D8 MAb (31D8 "bright"), but a minority (31D8 "dull") weakly bind the antibody and in this respect are similar to immature PMN precursors. The 31D8 "dull" PMN have impaired function compared with 31D8 "bright" PMN. In the present study, a PMN subpopulation that failed to migrate using the micropore filter assay accounted for 58 +/- 7% of adult PMN and was similar to the migrating subpopulation in regard to viability and phagocytic function. The nonmotile subpopulation had a higher percentage of bands (5 +/- 3% versus 1 +/- 2%, p less than 0.01) and decreased binding of 31D8 MAb compared with the motile subpopulation. Neonates had a larger nonmigrating PMN subpopulation and 31D8 "dull" PMN subpopulation than those of adults (76 +/- 3% versus 58 +/- 7%, p = 0.04 and 26 +/- 11% versus 8 +/- 2%, p less than 0.01, respectively). These data indicate that although PMN appear morphologically as a homogeneous population of cells, there exists a viable, nonmotile PMN subpopulation that may be less mature than the motile PMN subpopulation. They also indicate that impaired neonatal PMN motility may be attributable in part to an increased size of the nonmotile PMN subpopulation.