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The GCN2 kinase is shown to have a protective role in the regulation of intestinal inflammation during amino acid starvation in a mouse model of colitis. Gut inflammation reduction by amino acid starvation This study shows that the amino acid sensing protein kinase GCN2 suppresses gut inflammation during amino acid starvation. GCN2 deficiency correlates with impaired induction of autophagy in intestinal antigen presenting cells and epithelial cells, increased reactive oxygen species production and increased inflammasome activation in a mouse model for colitis. The integrated stress response (ISR) is a homeostatic mechanism by which eukaryotic cells sense and respond to stress-inducing signals, such as amino acid starvation. General controlled non-repressed (GCN2) kinase is a key orchestrator of the ISR, and modulates protein synthesis in response to amino acid starvation. Here we demonstrate in mice that GCN2 controls intestinal inflammation by suppressing inflammasome activation. Enhanced activation of ISR was observed in intestinal antigen presenting cells (APCs) and epithelial cells during amino acid starvation, or intestinal inflammation. Genetic deletion of Gcn2 (also known as Eif2ka4) in CD11c.sup.+ APCs or intestinal epithelial cells resulted in enhanced intestinal inflammation and T helper 17 cell (T.sub.H17) responses, owing to enhanced inflammasome activation and interleukin (IL)-1[beta] production. This was caused by reduced autophagy in Gcn2.sup.-/- intestinal APCs and epithelial cells, leading to increased reactive oxygen species (ROS), a potent activator of inflammasomes.sup.1. Thus, conditional ablation of Atg5 or Atg7 in intestinal APCs resulted in enhanced ROS and T.sub.H17 responses. Furthermore, in vivo blockade of ROS and IL-1[beta] resulted in inhibition of T.sub.H17 responses and reduced inflammation in Gcn2.sup.-/- mice. Importantly, acute amino acid starvation suppressed intestinal inflammation via a mechanism dependent on GCN2. These results reveal a mechanism that couples amino acid sensing with control of intestinal inflammation via GCN2., Author(s): Rajesh Ravindran [sup.1] , Jens Loebbermann [sup.1] , Helder I. Nakaya [sup.2] , Nooruddin Khan [sup.3] , Hualing Ma [sup.1] , Leonardo Gama [sup.2] , Deepa K. Machiah [sup.4] [...]

Starving for DENV vaccines: Nearly 50% of the world's population is considered at risk of infection with dengue virus (DENV), a mosquito-borne RNA virus that can potentially cause lethal disease. The efficacy of currently approved vaccines is poor in people who have not previously encountered DENV. Afroz et al. found that pretreatment of mice with the amino acid starvation mimetic halofuginone (HF) increased the adaptive immune response to a DENV vaccine. Known to activate the nutrient-sensing kinase GCN2, HF promoted phosphorylation of the translation initiation factor eIF2α in immune cells, increased germinal center formation, and increased neutralizing antibody responses. These data demonstrate how activation of this stress-induced kinase improves vaccination. Specific reduction in the intake of proteins or amino acids (AAs) offers enormous health benefits, including increased life span, protection against age-associated disorders, and improved metabolic fitness and immunity. Cells respond to conditions of AA starvation by activating the amino acid starvation response (AAR). Here, we showed that mimicking AAR with halofuginone (HF) enhanced the magnitude and affinity of neutralizing, antigen-specific antibody responses in mice immunized with dengue virus envelope domain III protein (DENVrEDIII), a potent vaccine candidate against DENV. HF enhanced the formation of germinal centers (GCs) and increased the production of the cytokine IL-10 in the secondary lymphoid organs of vaccinated mice. Furthermore, HF promoted the transcription of genes associated with memory B cell formation and maintenance and maturation of GCs in the draining lymph nodes of vaccinated mice. The increased abundance of IL-10 in HF-preconditioned mice correlated with enhanced GC responses and may promote the establishment of long-lived plasma cells that secrete antigen-specific, high-affinity antibodies. Thus, these data suggest that mimetics of AA starvation could provide an alternative strategy to augment the efficacy of vaccines against dengue and other infectious diseases. [ABSTRACT FROM AUTHOR]

PE/PPE genes, present in cluster with ESAT-6 like genes, are suspected to have a role in antigenic variation and virulence of Mycobacterium tuberculosis. Their roles in immune evasion and immune modulation of host are also well documented.We present evidence that PE32/PPE65 present within the RD8 region are co-operonic, co-transcribed, and co-translated, and play role in modulating host immune responses. Experiments with macrophage cell lines revealed that this protein complex suppresses pro-inflammatory cytokines such as TNF-α and IL-6 whereas also inducing high expression of antiinflammatory IL-10. Immunization of mice with these recombinant proteins dampens an effective Th1 response as evident from reduced frequency of IFN-δ and IL-2 producing CD4+ and CD8+ T cells. IgG sub-typing from serum of immunized mice revealed high levels of IgG1 when compared with IgG2a and IgG2b. Further IgG1/IgG2a ratio clearly demonstrated that the protein complex manipulates the host immune response favorable to the pathogen. Our results demonstrate that the co-transcribed and co-translated PE32 and PPE65 antigens are involved specifically in modulating anti-mycobacterial host immune response by hampering Th1 response. [ABSTRACT FROM AUTHOR]

The T-helper (Th) 1 T-cell response to purified protein derivative (PPD) is known to be suppressed in tuberculosis patients which favours intracellular survival of the bacilli. We demonstrate that the Mycobacterium tuberculosis heat shock protein 60 (Mtbhsp60) plays an important role to skew the anti-PPD T-cell response towards the Th2 type when macrophages were used as antigen presenting cells. We found that the PPD-induced IL-12 p40 was downregulated in macrophages by Mtbhsp60. The Mtbhsp60 preferentially induced Toll-like receptor (TLR) 2 without affecting TLR4 expression on macrophages. Interaction of Mtbhsp60 with TLR2 resulted in significant suppression of nuclear c-rel and consequently IL-12 p40 levels in PPD-activated macrophages. Our findings reveal a unique role of the Mtbhsp60 favouring development of Th2 type response by upregulating surface expression of TLR2 on macrophages which could be a survival strategy adopted by the bacilli. [ABSTRACT FROM AUTHOR]

Objective: Dengue is a viral infection endemic in more than 100 countries as per the WHO reports with approximately 5.2 million patients worldwide that spreads from mosquitoes to humans. Severe form of dengue fever can cause serious bleeding (low platelets) and death. Megakaryocytes are the immune cells responsible for the production of platelets. The molecular drivers behind platelet defects are mostly ambiguous. Here, we attempted to understand the distinct pathogen-elicited toll-like receptors (TLRs) functions in megakaryocyte biology. To understand the TLR induction and the molecular events that are governed in the mammalian system during dengue infection and to study TLR2-mediated cellular signaling-associated mechanisms with respect to their dimerization partners during dengue infection., Methods: In this study, we used the human Megakaryoblastic cells, DAMI, and treated them with TLR agonists (LPS and Zymosan) and Dengue virus (DNV-II)., Results and Discussion: TLR2 could play an important role by dimerizing with TLR1, TLR4, and TLR6, which we induced for functional characterization. We observed that megakaryocyte maturation markers CD-41 and CD-61 were elevated. This augmentation under the LPS and Zymosan system along with DNV Infection was further confirmed. Our analysis also suggested that activation of miR-125b and MAPK signaling led to lipid droplet elevation. This led us to analyze TLR-mediated consequences and their impact on megakaryocyte development under diverse pathogen-elicited conditions., Conclusion: Pathogenic challenges associated with toll-like receptor system activation could further our understanding of the platelet biogenesis mechanistic pathways under various pathogenic circumstances., Competing Interests: None., (AJTR Copyright © 2023.)

Blocking T cell co-stimulatory signals by anti-B7-1/B7-2 mAb is an attractive approach to treat autoimmune diseases. However, anti-B7-1/B7-2 mAb treatment is known to exacerbate autoimmune diseases through mechanisms not fully understood. Tumor necrosis factor alpha (TNF-alpha) and reactive oxygen species (ROS) also play important roles in determining the clinical outcome of autoimmune diseases. In this study, we demonstrate that the anti-B7-1 and the anti-B7-2 mAbs activate macrophages for higher induction of TNF-alpha and other effector responses such as bacterial cytotoxicity and production of ROS. Nuclear factor-kappaB (NF-kappaB) was found to be increased with anti-B7-1/B7-2 mAb treatment. Inhibition of NF-kappaB activity by over-expression of phosphorylation-defective I-kappaB alpha in anti-B7-1/B7-2 mAb-treated macrophages decreased TNF-alpha production. These data indicate that anti-B7-1 and anti-B7-2 mAbs can trigger innate-effector responses in macrophages by activating NF-kappaB-signaling pathway. Our results suggest that the B7 molecules are not only essential for induction of adaptive immune responses but also play roles in activation of innate immune responses.