Impaired Priming and Activation of the NADPH Oxidase in Patients with TLR Signaling Defects

Abstract

The NADPH oxidase of neutrophils (PMN) plays a key role in host defense by producing reactive oxygen species (ROS). Here we examine the molecular basis of priming and activation of the NADPH oxidase in PMN from patients with two types of TLR signaling defects: interleukin‐1 receptor associated kinase‐4 deficiency (IRAK4) and NF‐kB essential modulator deficiency. (NEMO) We observed Impaired superoxide generation by LPS‐primed and fMLP‐activated IRAK4 PMN that correlated with inefficient translocation of cytosolic factors: p47phox, p67phox and Rac2 and the flavo‐cytochrome subunit: gp91phox to the membrane. While IRAK4 PMN produced ≤ 5% of normal ROS levels, NEMO PMN displayed ~50% of normal ROS with normal translocation of regulatory subunits. Compared to LPS‐primed normal PMN, p47phox phosphorylation was significantly lower in IRAK4 PMN. We further observed the down‐modulation of p47phox phosphorylation and membrane translocation by phosphatidylinositol 3‐kinase (PI3K) inhibitor LY2940002 in LPS‐primed normal PMN. In addition the phosphorylated levels of signaling kinases p21‐activated kinase (Paks) (IRAK4 deficiency) and p38 (IRAK4 and NEMO deficiency) were significantly lower in PMN of TLR signaling defects. We, hereby, reveal the role of defective p38‐ PI3K‐ Rac‐Paks signaling pathway in IRAK4 deficiency patient in impairing the NADPH oxidase mediated ROS generation.Research support: NIH, NIAID