OP0040 HIPPOCAMPAL IMMUNE CELL TRAFFICKING AND A MYELOID PREDOMINANT INFLAMMATORY RESPONSE WITH ENHANCED ANTIGEN PRESENTATION AND DECREASED LEVELS OF NEUROTRANSMITTERS UNDERLY THE NEUROPSYCHIATRIC PHENOTYPE OF THE NZW/NZB MURINE LUPUS MODEL

Background:Neuropsychiatric events are common in patients with systemic lupus erythematosus (SLE), yet the underlying pathogenesis remains ill-defined, as the access to brain tissue is limited. We have previously shown that NZW/NZB F1 murine lupus model recapitulates the neuropsychiatric lupus phenotype including depressive-like behavior, increased rates of anxiety, cognitive dysfunction and motor disturbances, both at pre-nephritic and nephritic stages of the disease.Objectives:To dissect specific regions in the brain, which account for this phenotype and elucidate inflammatory and non-inflammatory mechanisms involved.Methods:Four distinct brain regions (hippocampus, amygdala, striatum and pre-frontal cortex) were dissected from brains of female C57BL/6 (WT) and NZW/NZB F1 mice at the age of 3 months (pre-nephritic) and 6 months (nephritic stage) (n=5-8/condition/experiment). Since most of the behavioral phenotype corresponds to the hippocampus, we first examined in depth the hippocampal pathology by bulk RNA sequencing, measurements of neurotransmitters levels via high-performance liquid chromatography (HPLC) and by immunophenotyping via flow cytometry analyses. For comparisons, statistical significance was indicated as a two-sided P<0.05.Results:Transcriptomic analysis revealed aberrant immune mediated response in the hippocampus of 6 month-old lupus mice compared to WT. Specifically, inflammatory pathways including both innate and adaptive immune responses, increased cytokine production, increased antigen presentation and immune cell trafficking, along with increased apoptosis and decreased cell proliferation suggest that immune aberrancies may lead to neuronal damage. These aberrancies were present in mice at 3 month-old, yet were progressed with time being more prominent at 6 month of age in lupus hippocampus. The RNA sequencing date were validated by immunophenotyping on lupus hippocampus demonstrating increased reactive GFAP+ astrocytes both at 3 and 6-month old mice. Activated IBA1+ microglia and CD11b+CD45hi CNS myeloid cells were increased only at 6 months of age. Furthermore, increased immune cell infiltration from the periphery including lymphocytes (CD45+CD11b-) mainly T cells (CD4+/CD8+) and monocytes (CD45+CD11b+Ly6G-Ly6C+), was evident only in 6 month-old lupus hippocampus compared to WT. Importantly, microglia cells in lupus hippocampus at 6 but not at 3 month of age, exhibited increased expression of antigen presenting markers including CD80, CD86 and MHC-II indicating that microglia cells may carry out the antigen presentation process seen in transcriptomic data. Low levels of serotonin and noradrenaline were observed at both 3 and 6 months of age in lupus mice; these aberrancies were mainly attributed to decreased serotonin synthesis as evidenced by intact serotonin metabolism (no differences were observed at its metabolite: 5-hydroxyindoleacetic acid). Analysis of the remaining regions of the brain combined with studies of metabolic activities of various brain regions by PET-CT scanning is in progress.Conclusion:Immune cell trafficking from the periphery combined with marked inflammatory response in the hippocampus underlie the neuropsychiatric phenotype in NZW/B murine lupus. Our data indicate increased expression of activated myeloid cells -including microglia- in the hippocampus of lupus mice culminating in increased antigen presentation and decreased neurotransmitter levels.References:[1]Nikolopoulos, D., et al. “THU0223 THE NEUROPSYCHIATRIC PHENOTYPE OF NZB/W LUPUS-PRONE MOUSE MODEL AT PRE-NEPHRITIC AND NEPHRITIC STAGES OF THE DISEASE: MURINE MODEL RECAPITULATES HUMAN DISEASE.” (2020): 334-335.Acknowledgements:This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 742390)Disclosure of Interests:None declared

Targeting Immune Cell Trafficking – Insights From Research Models and Implications for Future IBD Therapy

Inflammatory bowel diseases (IBDs), including Crohn’s disease (CD) and ulcerative colitis (UC) are multifactorial diseases with still unknown aetiology and an increasing prevalence and incidence worldwide. Despite plentiful therapeutic options for IBDs, the lack or loss of response in certain patients demands the development of further treatments to tackle this unmet medical need. In recent years, the success of the anti-α4β7 antibody vedolizumab highlighted the potential of targeting the homing of immune cells, which is now an important pillar of IBD therapy. Due to its complexity, leukocyte trafficking and the involved molecules offer a largely untapped resource for a plethora of potential therapeutic interventions. In this review, we aim to summarise current and future directions of specifically interfering with immune cell trafficking. We will comment on concepts of homing, retention and recirculation and particularly focus on the role of tissue-derived chemokines. Moreover, we will give an overview of the mode of action of drugs currently in use or still in the pipeline, highlighting their mechanisms and potential to reduce disease burden.

Immune cell trafficking across the blood-brain barrier in the absence and presence of neuroinflammation

To maintain the homeostatic environment required for proper function of CNS neurons the endothelial cells of CNS microvessels tightly regulate the movement of ions and molecules between the blood and the CNS. The unique properties of these blood vascular endothelial cells are termed blood-brain barrier (BBB) and extend to regulating immune cell trafficking into the immune privileged CNS during health and disease. In general, extravasation of circulating immune cells is a multi-step process regulated by the sequential interaction of adhesion and signalling molecules between the endothelial cells and the immune cells. Accounting for the unique barrier properties of CNS microvessels, immune cell migration across the BBB is distinct and characterized by several adaptations. Here we describe the mechanisms that regulate immune cell trafficking across the BBB during immune surveillance and neuroinflammation, with a focus on the current state-of-the-art in vitro and in vivo imaging observations.

Difference in Strain Pathogenicity of Septicemic Yersinia pestis Infection in a TLR2−/− Mouse Model

ABSTRACT Yersinia pestis is the causative agent of bubonic, pneumonic, and septicemic plague. We demonstrate that Toll-like receptor 2-deficient (TLR2−/−) mice are resistant to septicemic infection by the KIM5 strain of Y. pestis but not to infection by the CO92 Δpgm strain. This resistance is dependent on TLR2, the route of infection, and the isoform of YopJ. Elevated bacterial burdens were found in the spleens of CO92 Δpgm-infected animals by 24 h postinfection and in the livers by 4 days. The YopJ isoform present contributed directly to cytotoxicity and inflammatory cytokine production of bone marrow-derived macrophages from TLR2−/− mice. Immune cell trafficking is altered in CO92 Δpgm infections, with an increased neutrophil infiltration to the spleen 5 days postinfection. Immune cell infiltration to the liver was greater and earlier in KIM5-infected TLR2−/− mice. The functionality of the immune cells was assessed by the ability to develop reactive oxygen and nitrogen species. Our data suggest an inhibition of granulocytes in forming these species in CO92 Δpgm-infected TLR2−/− mice. These findings suggest that resistance to KIM5 in TLR2−/− mice is dependent on early immune cell trafficking and functionality.

Role of the lymphatic vasculature in cardiovascular medicine

The lymphatic vasculature has traditionally been considered important for removal of excessive fluid from the interstitial space, absorption of fat from the intestine and the immune system. Advances in molecular medicine and imaging have provided us with new tools to study the lymphatics. This has revealed that the vessels are actively involved in regulation of immune cell trafficking and inflammation. We now know much about how new lymphatic vessels are created (lymphangiogenesis) and that this is important in, for example, wound healing and tissue repair. The best characterised pathway for lymphangiogenesis is the vascular endothelial growth factor C (VEGF-C)/VEGFR3 pathway. Over recent years, there has been an increasing interest in the role of the lymphatics in cardiovascular medicine. Preclinical studies have shown that lymphangiogenesis and immune cell trafficking play a role in cardiovascular conditions such as atherosclerosis, recovery after myocardial infarction and rejection of cardiac allografts. Targeting the VEGF-C/VEGFR3 pathway can be beneficial in these conditions. The clinical spectrum of lymphatic abnormalities and lymphoedema is wide and overlaps with congenital heart disease. Important long-term complications to the Fontan circulation involves the lymphatics. New and improved imaging modalities has improved our understanding and management of these patients. Lymphatic leaks and flow abnormalities can be successfully treated, minimally invasively, with percutaneous embolisation. Future research will prove if the preclinical findings that point to a role of the lymphatics in several cardiovascular conditions will result in new treatment options.