Interleukin-21-dependent modulation of T cell antigen receptor reactivity towards low affinity peptide ligands in autoreactive CD8(+) T lymphocytes

Candidate Genetic and Molecular Drivers of Dysregulated Adaptive Immune Responses After Traumatic Brain Injury

Abstract Neuroinflammation is a significant and modifiable cause of secondary injury after traumatic brain injury (TBI), driven by both central and peripheral immune responses. A substantial proportion of outcome after TBI is genetically mediated, with an estimated heritability effect of around 26%, but because of the comparatively small datasets currently available, the individual drivers of this genetic effect have not been well delineated. A hypothesis-driven approach to analyzing genome-wide association study (GWAS) datasets reduces the burden of multiplicity testing and allows variants with a high prior biological probability of effect to be identified where sample size is insufficient to withstand data-driven approaches. Adaptive immune responses show substantial genetically mediated heterogeneity and are well established as a genetic source of risk for numerous disease states; importantly, HLA class II has been specifically identified as a locus of interest in the largest TBI GWAS study to date, highlighting the importance of genetic variance in adaptive immune responses after TBI. In this review article we identify and discuss adaptive immune system genes that are known to confer strong risk effects for human disease, with the dual intentions of drawing attention to this area of immunobiology, which, despite its importance to the field, remains under-investigated in TBI and presenting high-yield testable hypotheses for application to TBI GWAS datasets.

IL-15Rα-Independent IL-15 Signaling in Non-NK Cell-Derived IFNγ Driven Control of Listeria monocytogenes

Interleukin-15, produced by hematopoietic and parenchymal cells, maintains immune cell homeostasis and facilitates activation of lymphoid and myeloid cell subsets. IL-15 interacts with the ligand-binding receptor chain IL-15Rα during biosynthesis, and the IL-15:IL-15Rα complex is trans-presented to responder cells that express the IL-2/15Rβγ_c complex to initiate signaling. IL-15-deficient and IL-15Rα-deficient mice display similar alterations in immune cell subsets. Thus, the trimeric IL-15Rαβγ_c complex is considered the functional IL-15 receptor. However, studies on the pathogenic role of IL-15 in inflammatory and autoimmune diseases indicate that IL-15 can signal independently of IL-15Rα via the IL-15Rβγ_c dimer. Here, we compared the ability of mice lacking IL-15 (no signaling) or IL-15Rα (partial/distinct signaling) to control Listeria monocytogenes infection. We show that IL-15-deficient mice succumb to infection whereas IL-15Rα-deficient mice clear the pathogen as efficiently as wildtype mice. IL-15-deficient macrophages did not show any defect in bacterial uptake or iNOS expression in vitro. In vivo, IL-15 deficiency impaired the accumulation of inflammatory monocytes in infected spleens without affecting chemokine and pro-inflammatory cytokine production. The inability of IL-15-deficient mice to clear L. monocytogenes results from impaired early IFNγ production, which was not affected in IL-15Rα-deficient mice. Administration of IFNγ partially enabled IL-15-deficient mice to control the infection. Bone marrow chimeras revealed that IL-15 needed for early bacterial control can originate from both hematopoietic and non-hematopoietic cells. Overall, our findings indicate that IL-15-dependent IL-15Rα-independent signaling via the IL-15Rβγ_c dimeric complex is necessary and sufficient for the induction of IFNγ from sources other than NK/NKT cells to control bacterial pathogens.

NOD receptor and TLR9 modulation in severe acute pancreatitis‑induced intestinal injury

Severe acute pancreatitis (SAP) has a rapid onset and may cause multiple organ dysfunction syndrome (MODS), which has high mortality. Nucleotide binding oligomerization domain (NOD) receptor and Toll‑like receptor 9 (TLR9), a pattern recognition receptor in innate immunity, are involved in inflammation, immunity and pathogen recognition. The role and mechanism of the NOD receptor and TLR9 in early MODS of SAP‑induced intestinal injury, however, remain unclear. Wistar rats were divided into control, SAP, TLR9 inhibitor and NOD receptor activation groups. Reverse transcription‑quantitative polymerase chain reaction was used to analyze the expression of TLR9, NOD1 and NOD2 in the experimental treatment groups. Serum amylase, creatinine and alanine aminotransferase indices were measured, ELISA was used to determine the expression of tumor necrosis factor‑α (TNF‑α) and interleukin‑1β (IL‑1β) and western blot analysis was used to assess nuclear factor (NF)‑κB expression levels in intestinal tissues. Reactive oxygen species (ROS) levels and superoxide dismutase (SOD) activity were quantified by spectrometry. SAP and NOD receptor activation groups exhibited significantly elevated TLR9, NOD1, NOD2, TNF‑α, IL‑1β and nuclear factor (NF)‑κB levels compared with the control group. Furthermore, ROS production was increased, SOD activity was decreased and higher serum indices were exhibited, compared with the control group. The NOD receptor group presented more significant differences compared with the SAP group. The TLR9 inhibitor group exhibited opposite effects, with markedly decreased TLR9, NOD1, NOD2, TNF‑α, IL‑1β and NF‑κB levels. The TLR9 inhibitor group also presented reduced ROS production, increased SOD activity and lower serum indexes compared to the SAP group. The present study therefore indicated that NOD receptor and TLR9 may modulate the inflammatory response and further impact upon intestinal injury of SAP, via the regulation of NF‑κB expression and the oxidation/antioxidation balance, suggesting therapeutically targeting NOD receptor and TLR9 might be a useful approach for the treatment of severe acute pancreatitis.