Natural killer group 2D and CD28 receptors differentially activate mammalian/mechanistic target of rapamycin to alter murine effector CD8+ T-cell differentiation.

Memory CD8+ T cells are an essential component of anti-tumour and anti-viral immunity. Activation of the mammalian/mechanistic target of rapamycin (mTOR) pathway has been implicated in regulating the differentiation of effector and memory T cells. However, the mechanisms that control mTOR activity during immunity to tumours and infections are not well known. Activation of co-stimulatory receptors, including CD28 and natural killer group 2D (NKG2D), activate phosphatidylinositol-3 kinase and subsequently may activate the mTOR pathway in CD8+ T cells. This study compared the activation of the mTOR signalling pathway after co-stimulation through CD28 or NKG2D receptors in murine effector CD8+ T cells. Compared with CD28 co-stimulation, activation through CD3 and NKG2D receptors had weaker activation of mTORc1, as shown by decreased phosphorylation of mTORc1 targets S6K1, ribosomal protein S6 and eukaryotic initiation factor 4E binding protein 1. NKG2D co-stimulation also showed increased gene expression of tuberous sclerosis protein 2, a negative regulator of mTORc1, whereas CD28 co-stimulation increased gene expression of Ras homologue enriched in brain, an activator of mTORc1, and hypoxia-inducible factor-1α and vascular endothelial growth factor-α, pro-angiogenic factors downstream of mTORc1. Strong mTORc1 activation in CD28-co-stimulated cells also increased expression of transcription factors that support effector cell differentiation, namely T-bet, B lymphocyte-induced maturation protein (BLIMP-1), interferon regulatory factor 4, and inhibitor of DNA binding 2, whereas low levels of mTORc1 activation allowed for the expression of Eomes, B-cell lymphoma 6 (BCL6), and inhibitor of DNA binding 3 during NKG2D stimulation, and increased expression of memory markers CD62 ligand and CD127. These data show that compared with CD28, co-stimulation through the NKG2D receptor leads to the differential activation of the mTOR signalling pathway and potentially supports memory CD8+ T-cell differentiation.

NKG2D receptor activation of NF-κB enhances inflammatory cytokine production in murine effector CD8(+) T cells.

To induce strong immune responses, naïve CD8(+) T cells require stimulation through the TCR and costimulatory receptors. However, the biological effect of activating costimulatory receptors on effector T cells is still unclear. One costimulatory receptor that is likely to be engaged at the target site is NKG2D. This activating receptor is expressed on human and murine CD8(+) T cells with its ligands expressed on the majority of tumor cells and during some infections. In order to determine how activation of costimulatory receptors alters effector CD8(+) T cell functions, this study compared the activation of the NF-κB signaling pathway by two costimulatory receptors, CD28 and NKG2D. Compared to CD28 costimulation, activation of murine effector CD8(+) T cells through CD3 and NKG2D receptors enhanced activation of NF-κB as shown by increased phosphorylation of IKKα, IκBα, and NF-κB and IκBα degradation. NKG2D costimulation also increased activation, nuclear translocation, and DNA binding of NF-κB p65/p50 dimers. Activation of the NF-κB pathway also lead to increased gene expression and secretion of pro-inflammatory cytokines, including IFNα and IFNγ, and decreased gene expression and secretion of anti-inflammatory cytokines, including IL-10 and CCL2. Altered NF-κB activation also increased expression of the effector molecules TNFα, lymphotoxins α and ß, and Fas ligand, and increased tumor cell killing through FasL. These data show that compared to CD28 costimulation, activation through the NKG2D receptor leads to the differential activation of the NF-κB signaling pathway and potentially enhances the anti-tumor and anti-viral functions of effector CD8(+) T cells.

Accidental and nonaccidental poisonings as a cause of apparent life-threatening events in infants.

BACKGROUND: Apparent life-threatening events are a relatively common event in children for which there may be a number of causes. Previous reports have suggested that poisonings, either accidental or intentional, may be causes of some events. However, this theory has not been systematically studied. METHODS: We conducted a prospective, descriptive study of infants aged <2 years presenting to a pediatric emergency department of a large, urban tertiary care children's hospital with signs and symptoms of an apparent life-threatening event. All of the children presenting with an apparent life-threatening event were to undergo a standardized evaluation, which included obtaining a comprehensive urine toxicology screen. A positive toxicology screen result was defined as follows: a clinically insignificant screen result (identification of a medication that would not cause an apparent life-threatening event) or a clinically significant screen result (identification of a medication that could cause apnea or other event consistent with an apparent life-threatening event, even if it was a medication that the child was known to be taking). RESULTS: During the study period, 596 children presented to the emergency department with an apparent life-threatening event, and 274 (46.0%) had a toxicology screen performed. Of 274 toxicology screen results, 50 were considered truly positive (18.2%), and 23 positive screen results were considered clinically significant (23 of 274 [8.4%]). Thirteen toxicology screen results were positive for an over-the-counter cold preparation (13 of 274 [4.7%]). No parent admitted to having given his or her child an over-the-counter cold preparation. CONCLUSIONS: A substantial number of children presenting to the emergency department with an apparent life-threatening event had a positive toxicology screen result. In particular, a number of children were found to have been given an over-the-counter cold preparation. We would recommend that toxicology screens be included as part of the routine evaluation of children who present with an apparent life-threatening event.