Lecture 7 PDF - Sequential Activation Of Immunity In Viral Infection

Sequential Activation of Immunity in Viral Infection 1. First days of infection (Days 1-5) Increase in virus titer correlates with increase in viral replication. Produ...

Sequential Activation of Immunity in Viral Infection 1. First days of infection (Days 1-5) Increase in virus titer correlates with increase in viral replication. Production of cytokines of the innate immune system. Cytokines include: interferon-alpha, interferon-beta, tumor necrosis factor alpha and IL- 12. 2. Innate Immune system cytokines activate natural killer cells Natural killer cells begin to kill infected cells. Peak right after onset of infection. Natural killer cell activity begins to decline after about 5 days. Virus titer plateaus. 3. T-cell activation Typically after 5 days, T-cell mediated killing of infected cells occurs. T-cells kill remainder of infected cells and decrease virus titer significantly. T-cells are specific to an antigen. Body must eliminate most T-cells to avoid a T- cell sludge. Some T-cells are kept as memory cells. 1 Innate Immunity 2 Innate Immunity Appears early in phylogeny - phagocytes present in sponges, annelids, arthropods. Adaptive components appear in vertebrates and are most developed in mammals Innate immune system involved in protection of host against microbial infections and can greatly reduce or even eliminate microbial burden Interacts with the adaptive immune response: Components of the adaptive response activate the innate response Components of the innate response are required for the adaptive response 3 Non-induced Innate Responses are Active at Sites Throughout the Body Protective barriers part of the innate immune response throughout the body include: Skin- largest lymphoid organ. Enzymes within mouth and airway. Epithelial lining of airway, lung and alimentary canal actively provide protection. Microbiome/ virome within gastrointestinal tract. 4 Inflammation Once the epithelium is breached, the innate response takes over in an inflammatory response 1) Recruitment of effector cells/mechanisms; vasodilation, permeability. Presence of fluids such as blood and swelling due to permeability (fluids rushing to assist in repair). 2) Blood clotting to prevent pathogen spread Localized clotting mechanisms help prevent pathogen spread in addition to stoping the bleed. 3) Tissue remodeling to repair damage Components of the immune response such as macrophages assist in damage repair. 5  Some cells of the innate immune system Immune cells all come from Hematopoietic stem cells. Hematopoietic Stem Cell Hematopoietic stem cells are predominantly found in bone marrow. They differentiate in Myeloid and lymphocyte cell lineages. Myeloid cells include: neutrophils, macrophages and dendritic cells. Myeloid Lineage Lymphocyte Lineage Lymphocytes include: Natural killer cells and innate lymphoid cells. Lymphocyte precursors may also go on to differentiate into T cells and B cells. Innate Lymphoid Cells Cytokines Wound Healing Mucosal tissues 6 Recognition of “Danger” by the Innate Immune System Pathogen-associated molecular patterns (PAMPS) Components on the pathogen that are common to different pathogens and elicit a response Danger-associated molecular patterns (DAMPS) Body is programmed to recognizing problems that are not necessarily infections. Potential DAMPS include: Things that would induce Heat shock proteins. High Mobility Group B1 proteins (HMGB1) - a chromatin-associated protein that is secreted in response to “danger” and can induce dendritic cell maturation, induce pro-inflammatory cytokines Purine metabolites - ATP, adenosine, uric acid. Can be released upon necrotic cell death ATP is a danger signal because it is needed for all metabolic processes. Once cells die by necrosis, ATP and adenosine are released from cell signaling necrotic death. Uris acid forms crystals which activate innate pathways. Uric acid crystals are sharp and can poke holes and signal damage. DNA is a danger signal when found anywhere except the nucleus and mitochondria. 7  Illustration of Pathogen Associated Molecular Patterns (PAMPS) Three pathogens depicted are considered similar because they are all part of the same bacterial family. The PAMPS are recognized by the innate leukocytes. The unique structures (antigens) are what differentiate each pathogen. The antigens present on the pathogens are recognized by adaptive leukocytes. In summary: PAMPS = innate and Antigens = Adaptive From Mak and Saunders, Primer to the Immune Response, 2008 8  Natural Killer cells are cytotoxic cells with key roles in defense against viruses and tumors Natural Killer cell characteristics: Non-phagocytic Lymphoid lineage but do not rearrange receptors Kill by release of cytolytic granule contents in the area of an immunological synapse. Granules of the Natural killer cells contain Perforin and Proteases. Perforin pokes holes in the membranes Proteases (such as granzymes) digest the cell. Target cell dies by apoptosis. Apoptosis is a well controlled cell death that prevents the contents of the dying cell from being released throughout the body. Image from http://www.nutritionandhealthcenter.com/natural- 9 killer-cells/ Natural Killer cell responses upon encounter of SARS-CoV-2–infected cells and anti–SARS-CoV-2 vaccine. Aspects of Natural killer cell responses to SARS- CoV-2 virus: 1. Activation: When a Natural killer cell encounters a SARS-CoV-2 infected cell, the natural killer cells will begin to produce cytokines and respond to cytokines created by other cells. 2. Recognition: With healthy cells, natural killer cells recognize the “self” peptide and the natural killer cell is inhibited because there was no invader detected. Natural killer cells will detect a viral peptide on infected cells and proceed to activate NK cells. 3. Pathophysiology: in acute infection of COVID-19 Natural killer cell activation/maturation increases as severity of COVID-19 increases. The number of natural killer cells decreases as the infection become more severe. 4. Prevention: Upon receiving an mRNA based vaccine, there is a spike in natural killer cell activation. Eventually decreases days following vaccination. J Leukoc Biol., Volume 114, Issue 5, November 2023, Pages 507–512, https://doi.org/10.1093/jleuko/qiad031 The content of this slide may be subject to copyright: please see the slide notes for details.  The Neutrophil (also known as the “poly” or “PMN”) Characteristics of neutrophils: Neutrohils come from bone marrow. Myeloid precursor: neutrophils differentiate from a myeloid precursor. Short-lived (6hr)- but life extended by infection. 1011 produced/day Resident in blood Phagocytic cells: can take up antigens. They are the first cells recruited to site of infection Downloaded from: S tud entCon sult (on 18 June 2007 03:38 PM) © 2005 Elsevier  Neutrophils in COVID-19 Neutrophilia in patients with COVID-19 (large numbers of neutrophils) Neutrophilia is an increase in neutrophils. Neutropenia is a decrease in neutrophils. White blood counts can be low or normal, but neutrophils make up the bulk of the WBC, with lymphocytes in decreased numbers (lymphopenia). Neutrophil infiltrates in the lungs seen at autopsy. Neutrophilia found in patients that die of SARS-CoV-2. This contributes to death. Neutrophil netosis (neutrophil extracellular traps) – driven by IL-6 As a neutrophil dies, contents are released and DNA is scattered due to de-condesing of chromatin. In the event of Neutrophil Netosis the infectious agent (virus or bacteria) gets trapped by neutrophil extra cellular traps. https://www.researchgate.net/publication 12 /313464581_  Monocytes in SARS-CoV-2 Monocytes come from myeloid precursor. Monocytes differentiate into macrophages. Increased levels of circulating monocytes during acute infection that persist after recovery/viral clearance and in those with post-acute sequelae of Coronavirus-19 (PASC). Long covid is now referred to as PASC. Monocytes/Macrophages are major contributor to the cytokine storm in COVID-19 and persistence of cytokines in plasma after recovery. Changes in monocyte sub-populations persist for months post-COVID even without PASC Even if patients without PASC appear to be recovering well, there are still cytokines that persist. 13 Persistent CD169+ Monocytes Following SARS-CoV-2 Infection in Recovered and PASC CD169+ is a monocyte subpopulation marker that can be used to analyze presence of monocytes in patients. CD169+ is most affected in COVID-19. CD14 is a general marker. In healthy individuals: monocytes are present at 5% to 10%. In COVID-19 recovered patients: percentage of monocytes circulating remains high. In patients with PASC: monocyte count is signficantly increased and remain high overall. 14 10.3389/fimmu.2023.1151780  Type 1 Interferon in viral infection Type 1 interferon cytokine characteristics: Type 1 interferons are produced by by many cell types Antiviral effects. Augments and recruits NK cells Upregulates IL-12 receptors Upregulation of Class I and Class II MHC Regulation/induction of adaptive immune responses Induction of Th1 responses Th1 are inflammatory responses. Establishment of T memory: type 1 interferon help keep memory T cells. Used therapeutically Produced by many cell types; highest level are produced by plasmacytoid dendritic cells (pDC). Type 1 interferons are recognized by toll like receptors present on surface of dendritic cells or in endosomal compartments. There are also intracellular receptors for viral RNA called RIG 1 and MDA 5 which will turn on genes needed (interferon response factors and NF-KB) to activate type 1 interferons and type 3 interferons. Cell Death & Differentiation (2021) 28:3125–3139 15 Type 1 Interferon in COVID-19 There is a delayed production of type 1 interferon in COVID-19. Delayed response of type 1 interferons during early infection. Late, massive production of interferon type 1 (cytokines storm) in severe disease can be harmful to the host. 16 Type I/III IFN in Coronaviruses: possible therapeutics? Decreased Interferon production and interferon response genes expression in COVID-19, associated with severe disease. Type 1 Interferon: Murine hepatitis virus controlled through pDC type 1 IFN SARS-CoV-2 sensitive to type 1 interferon pretreatment Type 3 Interferon: SARS CoV-2 productively infects human gut enterocytes – type 3 interferons active in gut. Critical role of type 3 interferon in controlling SARS-CoV-2 infection, replication and spread in primary human intestinal epithelial 17 Dendritic Cells in COVID-19 Dendritic cells (DC) can be infected by some Coronaviruses, including original SARS. COVID-19 inhibits dendritic cell maturation into becoming antigen presenting cells. This inhibition leads to a weak adaptive immune response because innate cells can’t present antigen to T-cells and trigger them. Absolute numbers of dendritic cells change in blood in COVID-19 infection – important to look at absolute numbers/l rather than just percentages Plasmacytoid dendritic cells: the most potent producers of type 1 interferons. 18 Plasmacytoid Dendritic Cells: Specialized Virus Experts Plasmacytoid dendritic cells are factories of interferon type 1 production. Plasmacytoid dendritic cells have: Endosomal Toll like receptors 7: Constitutive IRF-7 recognize viral RNA. expression Endosomal Toll like receptor 9: recognize viral DNA. High constitutive levels of transcription factor IRF-7 which is required for induction of interferon alpha genes so that they are ready to go. Extensive ER An extensive endoplasmic reticulum. 19  pDC numbers and function in COVID-19 infection with and without dexamethasone (a corticosteroid used to dampen immune response) B. Looked at percent of 100 interferon alpha positive % of IFN-alpha Positive pDC plasmacytoid in patients pDC/l blood 80 with HSV. 60 Data suggests that decreased pDC will 40 contribute to the low type 20 1 interferon production 0 that is seen in COVID-19 because pDC are known SV SV SV + H + H + H to be interferon type 1 A. Study looks at decreased number of plasmacytoid dendritic cells in C x ex H de -t d generating factories. COVID-19 infected patients treated with dexamethasone vs not no s treated with dexamethasone. po Plasmacytoid count was low in COVID-19 patients regardless of dexamethasone treatment. Absolute number of dendritic cells falls dramatically in COVID-19 patients. 20  IFN- Production in HSV-stimulated pDC is Inversely Correlated with COVID-19 Severity Score post-dex HSV-stimulated IFN-+pDC 80 % of IFN-alpha Positive pDC Interferon production and covid- 19 severity score are inversely 60 correlated. As severity of disease increase, percentage of type 1 interferon 40 production decreases. 20 0 0 5 10 15 Severity Score  Viruses spend a lot of genetic energy in suppressing/moderating immune responses Viruses will attempt to suppress immune response by using the following methods: Inhibition of interferon production Pattern recognition evasion Inhibiting antigen presentation Decreasing MHC Class 1 expression on infected cells so that infected cells cannot be killed by T cells. Production of immunosuppressive cytokines Inhibiting natural killer cells 22 Coronaviruses inhibit type 1 Interferons Coronaviruses inhibit type 1 interferons using the following mechanisms: Hide in double-membraned structures inside cells, avoiding RIG-1 and endosomal toll-like receptors Inhibit RIG-1 activation (recognizes dsRNA in cytoplasm) Inhibit type 1 interferon induction in cells Inhibit type 1 interferon signaling through IFNAR (IFN receptor) ORF3b from SARS-CoV-2 is a potent interferon antagonist 23  Uninflected patients: CD4 and CD8 T cells are circulating. Epithelium not infected. No symptoms. Moderate COVID-19: immune response functioning well.Damaged epithelial cell. Cytokine production (TNF-alpha, IL-6 and IL-10). Upregulation of interferon gamma production. Lymphocyte production decreasing because they will be activated in lymph nodes. Cytokine storm. Large number of circulating cells. Severe decrease in lymphocytes, CD4 and CD8 T cells, but large increase in WBC due to increasing neutrophils. 24 Trained Immunity Innate immune cells don’t exhibit classical memory – i.e. unlike T and B memory cells (memory that can be reactivated). But, there is evidence for enhanced (and non-specific) responses based on antigenic history For example, Infants given BCG vaccine have decreased respiratory infections of all types in early life. Vaccines can provide heterologous protection against other infections. For example, flu vaccine may help decrease probability of becoming infected with SARS-CoV-2. Natural Killer cells activated against CMV “remember” that encounter and can be very efficient upon subsequent encounter “Trained Immunity” or ”innate memory” is not as long-lasting as classical memory form T and B cells. Trained or innate immunity may last months (or sometimes longer) rather than a lifetime. 25