Type 1 IFN Induction by Cytosolic Nucleic Acid Is Intact in Neonatal Mononuclear Cells, Contrasting Starkly with Neonatal Hyporesponsiveness to TLR Ligation Due to Independence from Endosome-Mediated IRF3 Activation

Abstract

Two million infants die each year from infectious diseases before they reach 12 mo; many of these diseases are vaccine preventable in older populations. Pattern recognition receptors represent the critical front-line defense against pathogens. Evidence suggests that the innate immune system does not fully develop until puberty, contributing to impaired response to infection and impaired vaccine responses in neonates, infants, and children. The activity of the pattern recognition receptor family of cytosolic nucleic acid (CNA) sensors in this pediatric population has not been reported. We show that in direct contrast to weak TLR-induced type I IFN in human cord blood mononuclear cells, cord blood mononuclear cells are capable of initiating a potent response to CNA, inducing both antiviral type I IFN and, unexpectedly, proinflammatory TNF-α. A deficiency in Rab11-GTPase endosome formation and consequent lack of IRF3 activation in neonatal monocytes is at least in part responsible for the marked disparity in TLR-induced IFN production between neonatal and adult monocytes. CNA receptors do not rely on endosome formation, and therefore, these responses remain intact in neonates. Heightened neonatal responses to CNA challenge are maintained in children up to 2 y of age and, in marked contrast to TLR4/9 agonists, result in IL-12p70 and IFN-γ generation. CNA sensors induce robust antiviral and proinflammatory pathways in neonates and children and possess great potential for use as immunostimulants or vaccine adjuvants for targeted neonatal and pediatric populations to promote cell-mediated immunity against invasive infectious disease.

Nucleic acid cytokine responses in obese children and infants of obese mothers

“…Deficiencies in the responses to TLR activation in children is an example of how the immune system of children and adults differs [12,13]. We have recently reported that Poly(I:C) and Poly(dA:dT), activators of the cytosolic nucleic acid sensors of the innate immune system, can activate the immune systems of neonates and infants as efficiently as in adults [9]. Given that many of the adjuvants in current use rely on activating TLR pathways, we hypothesise that Poly(I:C) or Poly(dA:dT) may be candidates for future childhood vaccines.…”

“…We have recently identified a potential novel adjuvant for childhood vaccines. In adults, Poly(I:C) or Poly(dA:dT), when transfected in to cells, activate cytosolic nucleic acid (CNA) sensors and induce Type I Interferon (IFN) production along with other proinflammatory cytokines such as Tumor Necrosis Factor α (TNFα) [9]. It has previously been shown that while other activators of the innate immune system such as Lipopolysaccharide (LPS) and CpG, TLR4 and 9 ligands respectively, function well in adults, they are less able to activate the immune system of neonates and young children [10][11][12][13].…”

An Analytically and Diagnostically Sensitive RNA Extraction and RT-qPCR Protocol for Peripheral Blood Mononuclear Cells

“…This highlights that our protocol represents a robust alternative to protein-based assays (e.g., when measuring changes in cytokine mRNA expression in PBMCs in response to specific in vitro stimulation). This work will significantly improve analytical capacity of studies relying on irreplaceable, relatively small or costly human samples (e.g., neonatal PBMCs) (66,67).…”

Immunometabolism and innate immunity in the context of immunological maturation and respiratory pathogens in young children

“…21,22 In addition, cell-surface TLR ligation (i.e., TLR4) is impaired by a failure to endocytose after ligation by lack of Rab11a activity in neonates. 23 Of interest, even children up to 5 years old still exhibit lower IL-12 production upon PBMC stimulation with TLR agonists than adults, but are still higher than neonates. 24 This implies that some limitations in either TLR or epigenetic regulation continue even past toddlerhood.…”

“…However, TLR signaling is known to be limited in innate immune cells of newborns . In addition, cell‐surface TLR ligation (i.e., TLR4) is impaired by a failure to endocytose after ligation by lack of Rab11a activity in neonates . Of interest, even children up to 5 years old still exhibit lower IL‐12 production upon PBMC stimulation with TLR agonists than adults, but are still higher than neonates .…”