Efficiency of neutrophil migration in the neonate

To assess release of neutrophils from the neutrophil storage pool (NSP) and subsequent neutrophil migration into tissue sites, polyvinyl sponge discs were placed into subcutaneous pockets in either newborn or 4-wk-old rats. After 20 hr, the sponges were removed, and the animals' NSP size and the number of neutrophils which had migrated into the sponges were measured. In response to the sponge stimulus, neonatal rats released 83.6 +/- 1.2% (mean +/- S.E.) of their NSP (106.3 +/- 15.3 X 10(5) neutrophils), whereas the older animals released 28.4 +/- 5.0% (628.5 +/- 124.4 X 10(5) neutrophils) of their NSP (P less than 0.001). Neonatal neutrophils displayed a decreased ability to successfully migrate from the NSP to the sponges. The proportion of released neutrophils accumulating in the sponges was 9.2 +/- 0.6% in the neonates, compared with 58.5 +/- 7,8% (P less than 0.001) in the 4-wk-old rats.