Newborn polymorphonuclear leukocyte aggregation: a study of physical properties and ultrastructure using chemotactic...

N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) and N-formyl-L-methionyl-L-phenylalanine (FMP) were used to investigate neutrophil (PMN) aggregation. Neutrophils were isolated from healthy adult volunteers and term newborn cord blood. Neutrophil aggregation was measured after the addition of FMLP and FMP. Adult PMN aggregation curves demonstrated initial aggregation with slow deaggregation. Newborn neutrophil aggregation curves showed slow aggregation with no deaggregation. These results were identical to the adult and newborn neutrophil aggregation curves produced by C5a. Newborn PMN aggregates examined by scanning electromicrography showed frequent, dense aggregates compared with fewer, less dense aggregates of adult PMNs. Adult and newborn PMN aggregates differed when compared by transmission electromicrographs (EM). Newborn PMNs were tightly bound with cell membrane projections; adult PMNs were loosely bound with no cell membrane projections. Cytochalasin-B pretreated adult and newborn PMN aggregates displayed close approximation of cell membranes with large numbers of cytoplasmic projections. Newborn neutrophils are irreversibly aggregated by FMLP and FMP whereas adult neutrophils display an aggregation-deaggregation reaction. EM studies suggest that this irreversible aggregation of untreated newborn neutrophils may differ from the irreversible aggregation of cytochalasin-B pretreated neutrophils.