Age-Dependent Maturation of Toll-Like Receptor-Mediated Cytokine Responses in Gambian Infants

Abstract

The global burden of neonatal and infant mortality due to infection is staggering, particularly in resource-poor settings. Early childhood vaccination is one of the major interventions that can reduce this burden, but there are specific limitations to inducing effective immunity in early life, including impaired neonatal leukocyte production of Th1-polarizing cytokines to many stimuli. Characterizing the ontogeny of Toll-like receptor (TLR)-mediated innate immune responses in infants may shed light on susceptibility to infection in this vulnerable age group, and provide insights into TLR agonists as candidate adjuvants for improved neonatal vaccines. As little is known about the leukocyte responses of infants in resource-poor settings, we characterized production of Th1-, Th2-, and anti-inflammatory- cytokines in response to agonists of TLRs 1-9 in whole blood from 120 Gambian infants ranging from newborns (cord blood) to 12 months of age. Most of the TLR agonists induced TNFα, IL-1β, IL-6, and IL-10 in cord blood. The greatest TNFα responses were observed for TLR4, -5, and -8 agonists, the highest being the thiazoloquinoline CLO75 (TLR7/8) that also uniquely induced cord blood IFNγ production. For most agonists, TLR-mediated TNFα and IFNγ responses increased from birth to 1 month of age. TLR8 agonists also induced the greatest production of the Th1-polarizing cytokines TNFα and IFNγ throughout the first year of life, although the relative responses to the single TLR8 agonist and the combined TLR7/8 agonist changed with age. In contrast, IL-1β, IL-6, and IL-10 responses to most agonists were robust at birth and remained stable through 12 months of age. These observations provide fresh insights into the ontogeny of innate immunity in African children, and may inform development of age-specific adjuvanted vaccine formulations important for global health.

Malaria Modifies Neonatal and Early-Life Toll-Like Receptor Cytokine Responses

“…The overall age-related patterns of cytokine responses to TLR ligands we observed here in infancy are consistent with those reported in the only study of its kind published to date, in subSaharan African (Gambian) infants, that used whole blood and a short-term (18-to 24-h) culture period, i.e., conditions almost identical to those we used (28). The principal similarities include the presence of robust IL-6 and IL-10 responses at birth and of proinflammatory TNF-␣ and IFN-␥ responses that increased markedly from birth through the first 3 months of life.…”

“…At all times, the balance between production of proand anti-inflammatory mediators is tightly regulated to allow efficient, protective immune responses to develop while preventing the pathological consequences of excessive inflammation (26). In the particular context of control of inflammatory activity in early life, a pivotal role for neonatal B cells producing IL-10 as a result of TLR9 activation has been reported (27), a role that is consistent with reports of robust TLR ligand-mediated IL-10 responses present at birth both in non-African and in African populations (28)(29)(30).…”

“…Nevertheless, and as seen both in Caucasian (47,48) and Gambian infants (28), we did find that R848 was the agonist that consistently induced the strongest proand anti-inflammatory cytokine responses in Beninese infants, while responses induced by the TLR9 agonist were relatively weak. Cytokine production in response to the TLR9 agonist nevertheless increased from birth up to 6 months of age, a pattern not seen in the comparable studies of European or African infants (28,49). These disparate findings may be explained (i) by the comparatively broad target populations of R848 that can stimulate pDC, mDC, monocytes, and B cells (50) and (ii) by the TLR9 ligand we used (ODN CpG 2216) that exerts selective activity only on pDC (46) as opposed to on both pDC and B cells (28,49).…”

Use of the Microparticle Nanoscale Silicon Dioxide as an Adjuvant To Boost Vaccine Immune Responses against Influenza Virus in Neonatal Mice

“…Many of the next-generation adjuvants, for example, glucopyranosyl lipid adjuvant (GLA) (6), a lipopolysaccharide mimic, target the Tolllike receptors (TLR), but the functionality of TLR is diminished during early life (7). In multiple studies, the production of the cytokine tumor necrosis factor (TNF) after exposure to TLR ligands has been shown to be age related (8,9).However, TLR are not the only pattern recognition receptors and it may be that targeting other receptors can boost neonatal responses; for example, the dectin-1 ligand curdlan has been shown to activate neonatal dendritic cells (DC) (10). The inflammasomes are another family of danger-sensing receptors (11) that respond to a wide range of cellular damage and infection, leading to the formation of a caspase 1 complex, which can catalyze the cleavage of pro-interleukin 1-beta (IL-1␤) into the active form.…”

“…Many of the next-generation adjuvants, for example, glucopyranosyl lipid adjuvant (GLA) (6), a lipopolysaccharide mimic, target the Tolllike receptors (TLR), but the functionality of TLR is diminished during early life (7). In multiple studies, the production of the cytokine tumor necrosis factor (TNF) after exposure to TLR ligands has been shown to be age related (8,9).…”