Diminished priming of neonatal polymorphonuclear leukocytes by lipopolysaccharide is associated with reduced CD14 expression

Abstract

Previous research in our laboratory has shown that polymorphonuclear leukocytes (PMN) from neonates are not primed effectively in vitro with lipopolysaccharide (LPS) (from Escherichia coli O111:B4) compared with priming of adult PMN. This finding led us to speculate that differences between neonatal and adult LPS receptors may account for the lower response by neonatal PMN to LPS. In these experiments, we investigated if CD14 or other LPS receptors contribute to the priming activity of PMN by LPS. We found that unprimed neonatal and adult PMN expressed similar numbers of CD14 (11.6 ؎ 9.2 versus 18.6 ؎ 2.7 fluorescence units [FlU]; P > 0.05) and LPS-binding sites (2.94 ؎ 1.4 versus 4.94 ؎ 0.79 FlU; P > 0.05). Monoclonal antibody against CD14 (MY4) did not significantly change the binding of LPS to adult unprimed PMN, suggesting that LPS receptors other than CD14 receptors are predominant on PMN. However, when PMN were pretreated with LPS (10 ng/ml) for 45 min at 37؇C, expression of CD14 on adult PMN increased to 33.8 ؎ 4.9 FlU (P < 0.05 versus unprimed adult PMN) while that on neonatal PMN showed little change, increasing to 17.2 ؎ 10.3 FlU (P > 0.05 versus unprimed neonatal PMN; P < 0.05 versus primed adult PMN). Furthermore, MY4 specifically blocked oxidative-radical production from PMN primed with LPS (10 ng/ml) compared with that from control PMN (P < 0.01). These studies suggest that LPS primes PMN by activating CD14 expression. We conclude that lower expression of CD14 or failure to up-regulate CD14 after LPS pretreatment contributes to the inability of neonatal PMN to be primed by LPS.

Human newborn polymorphonuclear neutrophils exhibit decreased levels of MyD88 and attenuated p38 phosphorylation in response to lipopolysaccharide

“…We have identified significant agespecific differences in the LPS activation of a major intracellular MAP kinase, p38, and have shown that newborn PMN have lower concentrations of MyD88, an important mediator of LPS signaling. In this and previous studies 10 we have shown no differences between adult and newborn PMN in the levels of the major LPS membrane receptors (CD14 and TLR-4). Moreover, many of the intracellular kinases implicated in LPS signaling (Erk, p38, Lyn, Hck, Fgr) are present in similar amounts in these cells.…”

“…34 Indeed, our findings of diminished LPS responses of newborn PMN are similar to those using cells from MyD88 -/mice or MyD88 truncated cells. 10 In such cells LPS-induced nitric oxide release and degranulation are diminished although responses to other stimuli are preserved. 30,[35][36][37] The increased susceptibility of human newborns to gram-negative bacterial infections is due to a variety of humoral and cellular factors.…”

“…For instance, LPS-induced CD14 upregulation and priming of the oxidative burst are diminished in newborn compared with adult PMN. [5][6][7][8][9][10] We hypothesize that the decreased functional responses of newborn PMN to LPS may be due to differences in their signaling pathways compared to those of adults.…”

Immune responses in mothers of term and preterm very-low-birth-weight infants

“…Another possibility is that there is a shift in the composition of circulating monocyte populations and that these differ between mothers of term infants and mothers of VLBW infants. A recent study has shown diminished expression of CD14 on neonatal monocytes and neutrophils (35). Furthermore, the expression of these receptors may be altered by steroid, endocrine, or other serumderived factors in mothers of VLBW infants.…”

Characterization of Memphis 37 strain of human respiratory syncytial virus in neonatal lambs

“…Once at the site of infection, neutrophils of infants do not function at the same level as those of adults (187). They have about half the amount of lactoferrin, a 30% reduction in bactericidial/permeability increasing protein (BPI), and impaired oxidase activity (188)(189)(190).…”