TLR9 Activation Induces Normal Neutrophil Responses in a Child with IRAK-4 Deficiency: Involvement of the Direct PI3K Pathway

Abstract

Polymorphonuclear neutrophils (PMN) play a key role in innate immunity. Their activation and survival are tightly regulated by microbial products via pattern recognition receptors such as TLRs, which mediate recruitment of the IL-1R-associated kinase (IRAK) complex. We describe a new inherited IRAK-4 deficiency in a child with recurrent pyogenic bacterial infections. Analysis of the IRAK4 gene showed compound heterozygosity with two mutations: a missense mutation in the death domain of the protein (pArg12Cys) associated in cis-with a predicted benign variant (pArg391His); and a splice site mutation in intron 7 that led to the skipping of exon 7. A nontruncated IRAK-4 protein was detected by Western blotting. The patient’s functional deficiency of IRAK-4 protein was confirmed by the absence of IRAK-1 phosphorylation after stimulation with all TLR agonists tested. The patient’s PMNs showed strongly impaired responses (L-selectin and CD11b expression, oxidative burst, cytokine production, cell survival) to TLR agonists which engage TLR1/2, TLR2/6, TLR4, and TLR7/8; in contrast, the patient’s PMN responses to CpG-DNA (TLR9) were normal, except for cytokine production. The surprisingly normal effect of CpG-DNA on PMN functions and apoptosis disappeared after pretreatment with PI3K inhibitors. Together, these results suggest the existence of an IRAK-4-independent TLR9-induced transduction pathway leading to PI3K activation. This alternative pathway may play a key role in PMN control of infections by microorganisms other than pyogenic bacteria in inherited IRAK-4 deficiency.

Leukotriene B4 Potentiates CpG Signaling for Enhanced Cytokine Secretion by Human Leukocytes

“…Compared with unstimulated cell controls, stimulation of human neutrophils with LTB 4 or CpG-ODN alone lead to a slight but detectable phosphorylation of both p38 kinase and JNK (Fig. 5A), as reported previously (33)(34)(35). More interesting was the fact that synergism was observed in p38 and JNK kinase activation when both LTB 4 and CpG-ODN stimulations were performed simultaneously.…”

Chromatin remodelling and autocrine TNFα are required for optimal interleukin-6 expression in activated human neutrophils

“…These comprise cell shape changes, CD62L shedding, priming for enhanced respiratory burst 17,[47][48][49] , chemotaxis, phagocytosis 17,50 and neutrophil extracellular trap formation induction 51 , lipid mediator production 18 , prolonged survival 49,52 and cytokine production (using, however, less pure neutrophil populations than in this study), including TNFa 53 and IL-6 (refs 48,53,54). Similarly, two studies 55,56 have reported that human neutrophils cultured in the presence of infectious respiratory syncytial virus produce IL-6 at 1 ng ml À 1 per 5 Â 10 6 cells per 3 h (498% neutrophil purity 55 ), or at 100 pg ml À 1 per 5 Â 10 5 cells per 12 h (497% purity 56 ).…”

Flow cytometric investigation of neutrophil oxidative burst and apoptosis in physiological and pathological situations

“…Pathogen recognition by TLRs promotes the activation of cellular signaling NF-jB and mitogen-associated protein kinase pathways and the subsequent activation of PMN functions for efficient bacterial clearance. The major role of the TIR-IRAK signaling pathway in immunity to infections by pyogenic bacteria is illustrated by the recent description of children with inherited IRAK-4 deficiency associated with recurrent life-threatening and invasive bacterial infections (33,34).…”