Members of the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) superfamily share an intracytoplasmic Toll-IL-1 receptor (TIR) domain, which mediates recruitment of the interleukin-1 receptor-associated kinase (IRAK) complex via TIR-containing adapter molecules. We describe three unrelated children with inherited IRAK-4 deficiency. Their blood and fibroblast cells did not activate nuclear factor kappaB and mitogen-activated protein kinase (MAPK) and failed to induce downstream cytokines in response to any of the known ligands of TIR-bearing receptors. The otherwise healthy children developed infections caused by pyogenic bacteria. These findings suggest that, in humans, the TIR-IRAK signaling pathway is crucial for protective immunity against specific bacteria but is redundant against most other microorganisms.

SUMMARY Most autoreactive B cells are normally counterselected during early B cell development. To determine whether Toll-like receptors (TLRs) regulate the removal of autoreactive B lymphocytes, we tested the reactivity of recombinant antibodies from single B cells isolated from patients deficient for IRAK-4, and MyD88, whose cells do not respond to TLRs except TLR3 and from UNC-93B-deficient patients whose cells are irresponsive to TLR3, TLR7, TLR8 and TLR9. All patients suffered from defective central and peripheral B cell tolerance checkpoints resulting in the accumulation of large numbers of autoreactive mature naïve B cells in their blood. Hence, TLR7, TLR8, and TLR9 may normally prevent the recruitment of developing autoreactive B cells in healthy donors. Paradoxically, IRAK-4-, MyD88- and UNC-93B-deficient patients do not display autoreactive antibodies in their serum nor develop autoimmune diseases revealing that IRAK-4/MyD88/UNC-93B pathways blockade is likely to thwart the development of autoimmunity in humans.

The expression of uncoupling protein 2 (UCP2) was reduced in macrophages after stimulation with lipopolysaccharide (LPS). The physiological consequence and the regulatory mechanisms of the UCP2 down-regulation by LPS were investigated in a macrophage cell line, RAW264 cells. UCP2 overexpression in RAW264 cells transfected with eukaryotic expression vector containing ucp2 cDNA markedly reduced the production of intracellular reactive oxygen species. Furthermore, in the UCP2 transfectant, nitric oxide (NO) synthesis, inducible NO synthase (NOS II) protein, NOS II mRNA, and NOS II promoter activity were definitely decreased after LPS stimulation compared with those in parental RAW264 or RAW264 cells transfected with the vector alone. Reporter assays suggested that an enhancer element was located in the region of intron 2 of the UCP2 gene and that the UCP2 expression was down-regulated not by the 7.3-kb promoter region but by the 5 region of the UCP2 gene containing two introns. Deletion of intron 2 resulted in the low transcriptional activities and abolishment of the LPS-associated negative regulation. In addition, the mRNA expression of transfected UCP2 was suppressed in RAW264 cells transfected with expression vector containing UCP2 genomic DNA, but was markedly increased in cells transfected with the vector containing UCP2 intronless cDNA. These findings suggest that the LPS-stimulated signals suppress UCP2 expression by interrupting the function of intronic enhancer, leading to an up-regulation of intracellular reactive oxygen species, which activate the signal transduction cascade of NOS II expression, probably to ensure rapid and sufficient cellular responses to a microbial attack. U ncoupling protein 2 (UCP2) is a recently discovered member of the mitochondrial inner membrane carrier family with high homology to the brown adipose tissue-specific proton transporter, UCP1 (1-3). Because the gene ucp2 resides within a region of genetic linkage to obesity (1) and its product UCP2 uncouples respiration (4), a role in energy dissipation has been proposed. Mice lacking Ucp2 after targeted gene disruption, however, are not obese and have a normal response to cold exposure or high-fat diet (5). On the other hand, it has been proposed that UCP2 limits production of reactive oxygen species (ROS) by decreasing the mitochondrial membrane potential (6). Indeed, Ucp2 Ϫ/Ϫ mice are resistant to Toxoplasma gondii infection, and macrophages of the mutant mice have higher levels of ROS (5), which are associated with higher cytolytic activity (7). In addition, unlike UCP1, expression of UCP2 teems in spleen, lung, and isolated macrophages (1, 2, 8). These findings suggest a role for UCP2 in immunity or inflammatory responsiveness.Recognition of lipopolysaccharide (LPS) is crucial for host antimicrobial defense reactions (9, 10). Nitric oxide (NO) production by the inducible isoform of NO synthase (NOS II) after LPS stimulation plays a pivotal role in numerous and diverse biological functions, in particular, as a principal mediat...