Mechanisms underlying reduced responsiveness of neonatal neutrophils to distinct chemoattractants

Potential mechanisms underlying impaired chemotactic responsiveness of neon atal neutrophils were investigated. Two distinct chemoattractants were comp ared: bacterially derived N-formyl-methionyl-leucyl-phenylalanine (fMLP) an d a unique chemotactic monoclonal antibody, designated DL1.2, which hinds t o a neutrophil antigen with an apparent molecular mass of 120 kDa. Chemotax is of neutrophils toward fMLP, as well as DL1.2, was reduced in neonates wh en compared with adult cells. This did not appear to be a result of decreas ed fMLP receptor or DL1.2 antigen expression by neonatal neutrophils. fMLP, but not DL1.2, induced a rapid increase in intracellular calcium in adult and neonatal cells, which reached a maximum within 30 s. The calcium respon se of cells from neonates to fMLP was reduced when compared with adult cell s, and an unresponsive subpopulation of neonatal neutrophils was identified . NF-kappaB nuclear binding activity induced by fMLP and DL1.2, as well as expression of the p65 NF-kappaB subunit and I kappaB alpha, was also signif icantly reduced in neonatal cells, when compared with adult cells. In contr ast, although fMLP, but not DL1.2, activated p42/44 and p38 mitogen-activat ed protein (MAP) kinases in neutrophils, no differences were observed betwe en adults and neonates. Chemotaxis of adult and neonatal neutrophils, towar d fMLP and DL1.2 was also blocked to a similar extent by inhibitors of phos phatidylinositol 3-kinase, as well as an inhibitor of NF-kappaB. These find ings indicate that reduced chemotactic responsiveness in neonatal neutrophi ls is a result of, at least in part, aberrations in chemoattractant-induced signaling. However, the biochemical pathways mediating this defect appear to be related to the specific chemoattractant.