Uptake of extracellular calcium by neonatal neutrophils

Bacterial Sepsis in the Newborn Infant: Developmental Deficiencies in Neutrophils and the Role of Neutrophil Transfusion

Bacterial sepsis is an important cause of morbidity and mortality in newborns. Group B streptococci and Es cherichia coli are the primary causative organisms. New and theoretically more effective antibiotics have not im proved survival. Because the neonate has defects in the immune response, new forms of therapy may be able to improve outcome by correcting or circumventing those deficiencies. The neutrophil has a substantial role in antibacterial defense, yet neonatal neutrophil function is limited by impaired chemotaxis, phagocytosis, and in tracellular killing. The supply of neonatal neutrophils is restricted by a small neutrophil reserve, a delay in mobilization of neutrophils from the bone marrow re serve after bacterial invasion, a small granulocytopoietic progenitor cell reserve, and a limited ability to acceler ate proliferation of progenitor cells during bacterial in fection. Recent studies of neutrophil transfusions in in fected neonates suggest a beneficial effect at least in certain situations. Exchange transfusion with fresh whole blood may be an alternative to transfusion with neutro phils obtained by apheresis. The ultimate role of neutro phil transfusions as an adjunct therapy for neonatal sep sis remains to be determined.

Calcium mobilization in C5a-stimulated adult and newborn bovine neutrophils

Calcium (Ca2+) is an important second messenger central to many neutrophil (PMN) functional activities. Impaired Ca2+ mobilization in newborn PMNs following membrane perturbation could be one of the mechanisms underlying observed abnormalities in neonatal PMN function. To compare Ca2+ mobilization in bovine newborn and adult PMNs, cytosolic Ca2+ responses after stimulation with recombinant human C5a (rHC5a) were measured. PMNs from normal newborn calves (N = 6) and adult cows (N = 5) were loaded with fura-2/AM for 60 min at room temperature and the fluorescence changes monitored following stimulation with 0.1, 1, 10, or 50 nM rHC5a in Ca2(+)-containing buffer. Resting levels of Ca2+ in both newborn (54.6 +/- 1.9 nM) and adult (57.3 +/- 1.8 nM) bovine PMNs were comparable. After stimulation with rHC5a, a rapid rise of cytosolic Ca2+ was observed, which peaked within 20 sec and was followed by a sustained phase of elevated Ca2+ lasting up to 20 min. There were no significant differences (P greater than 0.05) in peak levels of cytosolic Ca2+ obtained by newborn and adult PMNs at 0.1, 10, and 50 nM rHC5a. At 1 nM rHC5a, newborn PMNs reached significantly (P less than 0.05) higher levels of cytosolic Ca2+ (217.9 +/- 21.7 nM) than did adult PMNs (158.7 +/- 7.9 nM). At 1 nM rHC5a, newborn PMNs also sustained higher levels of cytosolic Ca2+ for 3 min following the peak. At all concentrations of rHC5a tested, the time required to reach the peak and the duration of the peak were comparable in both populations. In the absence of extracellular Ca2+ (Ca2(+)-free buffer with 1 mM EGTA), resting levels of cytosolic Ca2+ were lower in both newborn (33.3 +/- 2.9 nM) and adult PMNs (27.9 +/- 2.4 nM) and the magnitude of the peak response to rHC5a was diminished at all concentrations of agonist. Additionally, in the absence of extracellular Ca2+, the return to basal cytosolic Ca2+ levels occurred rapidly and the sustained phase of increased cytosolic Ca2+ seen with rHC5a-stimulated PMNs in Ca2(+)-containing buffer was virtually eliminated. These results indicate that bovine PMNs respond well to rHC5a, that stimulated newborn bovine PMNs can mobilize Ca2+ as efficiently as adult PMNs, and that the sustained cytosolic Ca2+ response to rHC5a in both age groups requires both release of Ca2+ from intracellular stores as well as influx of extracellular Ca2+. Such data suggest that observed functional deficits in newborn bovine PMNs are probably not related to improper mobilization of Ca2+ following stimulation.

Linkage between neutrophil degranulation and calcium discharge

Calcium flux across organelle and plasma membranes is an important event in neutrophil activation. We measured calcium discharge into the media from neutrophils stimulated with formyl-methionyl-leucyl-phenylalanine after treatment with cytochalasin b. Cytochalasin markedly potentiated calcium efflux from stimulated neutrophils, and similarly promoted release of lysosomal enzymes into the media. Colchicine neither reproduced nor modified the cytochalasin effect. Neutrophil cytoplasts discharged very little calcium in response to stimulation, and discharge was not significantly altered by cytochalasin b. These findings indicate that neutrophil degranulation is accompanied by efflux of calcium into the media, and suggest that the neutrophil granules constitute a source of mobilizable calcium which could be used to modify the extracellular microenvironment.