Selective Impairment of TLR-Mediated Innate Immunity in Human Newborns: Neonatal Blood Plasma Reduces Monocyte TNF-α Induction by Bacterial Lipopeptides, Lipopolysaccharide, and Imiquimod, but Preserves the Response to R-848

Abstract

Newborns are at increased risk of overwhelming infection, yet the mechanisms underlying this susceptibility are incompletely defined. In this study we report a striking 1- to 3-log decrease in sensitivity of monocytes in human neonatal cord blood, compared with monocytes in adult peripheral blood, to the TNF-α-inducing effect of multiple TLR ligands, including bacterial lipopeptides (BLPs), LPS, and the imidazoquinoline compound, imiquimod. In marked contrast, TNF-α release in response to R-848, a TLR ligand that is a congener of imiquimod, was equivalent in newborn and adult blood. Differences in ligand-induced TNF-α release correlated with divergent ligand-induced changes in monocyte TNF-α mRNA levels. Newborn and adult monocytes did not differ in basal mRNA or protein expression of TLRs or mRNA expression of functionally related molecules. Newborn monocytes demonstrated diminished LPS-induced, but equivalent R-848-induced, phosphorylation of p38 mitogen-activated protein kinase and altered BLP- and LPS-induced acute modulation of cognate receptors, suggesting that the mechanism accounting for the observed differences may be localized proximal to ligand recognition by surface TLRs. Remarkably, newborn plasma conferred substantially reduced BLP-, LPS-, and imiquimod-induced TNF-α release on adult monocytes without any effect on R-848-induced TNF-α release, reflecting differences in a plasma factor(s) distinct from soluble CD14. Impaired response to multiple TLR ligands may significantly contribute to immature neonatal immunity. Conversely, relative preservation of responses to R-848 may present unique opportunities for augmenting innate and acquired immunity in the human newborn.

Responsiveness of human monocytes to the commensal bacterium Staphylococcus epidermidis develops late in gestation

“…TLR4 was expressed on a smaller subset of monocytes in preterm infants, but the expression was also equivalent across groups. Similar levels of mRNA and of protein expressions of TLR2 and TLR4 are reported in neonatal cells of term infants and in adult cells (35), whereas another study found that TLR4 expression increased with increasing GA (36). We conclude that differences in responses to SE in preterm infants are unlikely to result from GA-related increases in TLR2 expression.…”

Attenuated innate immune defenses in very premature neonates during the neonatal period

“…The measure of responses on whole blood provides a more global determination of anti-microbial responses. Indeed, previous studies have demonstrated that neonatal plasma suppresses TLR-mediated cytokine production, indicating that both cellular and soluble humeral factors are important in the functional determination of immune responsiveness (13,14).Our data are consistent with previous studies that have measured a low surface expression of TLRs on blood mononuclear cells of preterm neonates, with TLR2 and TLR4 expression increasing during the first 2 mo of age (15). However, because TLR-dependent cytokine responses generally correlate poorly with their corresponding receptor gene or protein expression, it is important to validate the impact of a reduced expression of PRR at the functional level by examining relevant cytokine responses (6).…”

TLR7/8 Triggering Exerts Opposing Effects in Acute versus Latent HIV Infection

“…Based on published work (5,13,14), we usually tested cultures with R-848 at 1 g/ml to investigate its effects on HIV replication. Titrating R-848 from 10 -0.01 g/ml revealed a clear dose dependency: R-848 gradually lost its anti-HIV activity at concentrations Ͻ 0.1 g/ml (Fig.…”

“…The B cell line Namalwa was cultivated in RPMI 1640, 15% FCS, 1 mM sodium pyruvate, 1 mM nonessential amino acids, and 1% P/S. R-848 (InvivoGen) was used mainly at 1 g/ml (5,13,14), polyinosic: polycytidylic acid (poly(I:C); Amersham Biosciences) at 20 g/ml, flagellin from Salmonella typhimurium (provided by J. C. Sirard (Institut de Biologie de Lille, Université E0364 1, Lille, France)) at 100 g/ml, peptidoglycan from Staphylococcus aureus (Fluka) at 10 g/ml and LPS (Escherichia coli K-235; Sigma-Aldrich) at 20 g/ml. Sequences of phosphothioate-modified ssRNA (i.e., ssRNA40, 41, and 42) were identical to those published by Heil et al (6); in particular the RNA40 is a 20 mer identical to the U5 region from 108 to 127; RNA41 and 42 are 20 mer where all U or G nucleotides were replaced with adenosine, respectively (IBA).…”