Toll-like receptor signaling in neonatal sepsis and inflammation: a matter of orchestration and conditioning

Abstract

Altered neonatal Toll-like receptor (TLR) function is hypothesized to contribute to the heightened susceptibility to infection and perpetuated inflammation in term and preterm neonates, clinically evident in neonatal sepsis and increased rates of inflammatory disorders. Current data indicate that basal TLR expression in term neonates equals adult expression patterns, while expression in preterm infants seems to increase, depending on gestational age. Regarding TLR signaling, some studies suggest TLR incompetence in neonates associated with impaired pro-inflammatory responses, others describe neonatal TLR function well developed and allude to its hyper-inflammation tendency. We discuss the competing positions and considerable limitations of research approaches and conclude that neonatal innate immunity is not generally less able to respond to TLR stimulation. Moreover, we describe pre-conditioning factors other than immaturity having a comparable impact. In the long term, better understanding of the complex interplay of pre- and postnatal conditions and maturation-dependent neonatal TLR function may provide new therapeutic approaches.

Keywords::

• BPD
• inflammatory disorders
• innate immunity
• NEC
• neonatal sepsis
• PWM
• TLR signaling
• Toll-like receptors

Financial & competing interests disclosure

CP Speer has a consultancy agreement with Chiesi Farmaceutici S.p.A. (Italy). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • Basal Toll-like receptor (TLR) expression in immune cells of term neonates has been shown to equal adult expression patterns. In preterm neonates, findings suggest a gestational-age dependent increase in TLR expression.

• • TLR sensor function seems to be well developed in neonates, and innate immune function appears similarly able to respond to TLR stimulation as the adult counterpart but exhibits rather qualitatively different responses.

• • Further investigations are needed to define the extent of modification of neonatal TLR-mediated cytokine responses by antenatal and perinatal conditioning, the impact of immaturity and the influence of potential inborn immunological deficiencies on altered TLR responses in neonatal study collectives.

• • TLR signaling has been demonstrated to be a highly complex interplay in terms of both signaling cascades and a variety of co-stimulatory and regulatory molecules modifying TLR response making it even more difficult to integrate neonatal inflammation in one model and to derive therapeutic strategies.

Notes