BMS150 Barrier Immunity PDF

Immunology V Concepts in Barrier Immunity BMS 150 Week 3 Barrier Immunity - Objectives Relate the polarization of T-helper cells to common infectious or allergic diseases in the skin and upper respiratory tract List the key mediators secreted by eosinophils and mast cells and briefly describe the fu...

Immunology V Concepts in Barrier Immunity BMS 150 Week 3 Barrier Immunity - Objectives Relate the polarization of T-helper cells to common infectious or allergic diseases in the skin and upper respiratory tract List the key mediators secreted by eosinophils and mast cells and briefly describe the function of each and whether they are located in granules or produced de novo Relate the function of IgE and its Fc receptor to the activity of mast cells and eosinophils Describe the appearance of the histologic structures and key immunological cells that are present in the barrier tissues of the skin and the upper respiratory tract Describe the basic functions/immunologic advantages of Th1, Th2, and Th17 responses at barrier structures Briefly compare the characteristics of type 1 and type 2 inflammation, focusing on tissue effects and major immune pathways activated Barrier Immunity - Objectives Describe the mediators released as well as the cellular and tissue effects during a Th1, Th2, or Th17 response at the skin or upper respiratory tract mucosal barrier Describe the activation of innate lymphoid cells at barrier tissues and how they impact the overall immune response Describe how PRRs in epithelial cells and innate immune cells impact the development of immune responses at the skin and upper respiratory tract barrier tissues Describe how defects in the barrier function of the skin can lead to the development of a Th2 response in atopic dermatitis Describe how a viral upper respiratory infection results in a predominantly “Type 1” inflammatory response Key Information to Review (from prior lectures) Th polarization The production of IgE by B-cells PRRs (Innate Immunity lectures 1 and 2) ▪ Extracellular vs. Intracellular? And back to semester 1! ▪ Filaggrin and tight junctions in the skin Th2 cells – a quick review Polarizing cytokines that transform a naïve Th into a Th2: IL-4 is the major polarizing cytokine ▪ The source of IL-4 is a bit of a mystery – when a dendritic cell presents antigen to a naïve Th, the dendritic cell does not seem to secrete IL-4 Main determining transcription factor: GATA-3 ▪ All Th2 cells express GATA-3 Th2 effector functions: ▪ Production of IgE IgE enhances mast cell immune and eosinophil activity ▪ Secretion of IL-4, IL-5, IL-13 IL-4 is potent Th2 polarizing factor (positive feedback) and also increases antibody secretion by B-cells IL-5 aids eosinophil activity and migration IL-13 increases the production of IgE Antibody production: Th1 & Th2 review Different cytokines secreted by the T-helper cells will induce class switching ▪ TH1 cells secrete IFN-y which stimulates class switching to IgG subtypes ▪ TGF-beta and Retinoic Acid seem to stimulate class switching to IgA ▪ TH2 cells secrete IL-4 & IL5, which stimulates class switching to IgE IL-21 IL-4 Also secretion of large amounts to IgM Kuby Immunology (6th ed) Figure 11-19, page 271 Antibody classes: IgE review Secreted as a monomer in small quantities Functions: ▪ Binds to cells with an Fc receptor for IgE triggering degranulation of granulocytes Eosinophils, basophils, mast cells TOP: Adapted from: https://upload.wikimedia.org/wikipedia/commons/1/14/2221_Five_Classes_of_Antibodies_new.jpg BOTTOM: Kuby Immunology (6th ed) Figure 4-16, page 94 Tight Junctions - Review Key proteins: Claudins – trans-membrane proteins that can act as channels for small molecules (paracellular) Occludin – trans-membrane protein, function not clear Junctional adhesion molecules (JAM) ▪ Trans-membrane protein that may mediate permeability to larger molecules ZO-proteins ▪ Important in tight junction formation, interact with the cytoskeleton https://commons.wikimedia.org/wiki/File:Life_cycle_and_protein_associations_of_connexins.jpg The Skin – Review As skin matures from deeper layers, junctions are modified ▪ Loss of hemidesmosomes (no contact with the basement membrane) ▪ Modification of desmosomes ▪ Tight junctions remain Net result – the “outside” surface of the skin is flattened layers of dead “bags” of keratin and filaggrin linked by tight junctions ▪ Filaggrin helps compact keratin and attracts water, aiding in skin moisturization Barrier Immunity – the Players in the Upper Respiratory Tract and Skin Mast cells Eosinophils Innate lymphoid cells (ILCs) Epithelial cells Secondary lymphoid tissue of the upper respiratory and cutaneous barriers Already discussed – to some extent: Dendritic cells Macrophages Lymphocytes Mast Cells Derived from granulocyte-monocyte progenitors ▪ Seem to leave the bone marrow as a relatively undifferentiated cell then mature in the peripheral tissues that they migrate into ▪ Signals that promote survival and migration may include: High circulating IgE IL-4, IL-33 Their survival is inhibited by IFN- ▪ If more mast cells are needed, can recruit more from the bone marrow OR resident cells can divide Once they migrate to a tissue, they tend to live for months ▪ Live within the connective tissue layers of a barrier (i.e. dermis, lamina propria) Mast Cells - Function Express the Fc receptor for IgE ▪ Circulating IgE accumulates on mast cell membranes and serves as a “specific” receptor for antigen ▪ When antigen binds to IgE which is attached to the mast cell membrane → degranulation (see mast cell granules next slide) Express many PRRs – when they are activated, degranulation can also occur: ▪ TLRs, NLRs, C-type lectins ▪ Complement receptors (C3a, C5a) Granule contents are pre-synthesized – when the mast cell is activated, they can be released instantly or a few at a time ▪ Lipid mediators – prostaglandins, leukotrienes, and some cytokines – are also released by mast cells but are synthesized “as needed” Mast Cells – Early Mediators Mediator Granule or Produced? Function Histamine Granule Increased permeability of small vessels, increased mucous secretion, vasodilation, contraction of smooth muscle Heparin Granule Platelet activation, coagulation Chemotactic factors Produced Attract eosinophils and neutrophils (Eotaxin and NCF-A, respectively). Can also attract monocytes later during fibrosis and repair (CCL-2) Prostaglandins Leukotrienes Produced LTs – smooth muscle constriction, chemotaxis, increased vasc. permeability PGs – vasodilation, increased vasc. permeability Proteases Granule Inflammatory – degradation of type IV collagen, activation of complement, generation of bradykinin, activation of coagulation ?Antinflammatory? – may degrade cytokines Cytokines Both IL-4, TNF- - immediate release (granule) – type II inflammation IL-4, TGF-, IL-6, IL-18 – released later, type depends on stimulus (produced) Mast Cells – Acute Response Integration This is also known as a Type I hypersensitivity response – more about other hypersensitivities later Histamine Heparin Proteases IL-4, TNF-alpha How Do We Organize Mast Cell Activity? Sequentially: 1. Mast cells are recruited into tissue 2. Become sensitized (PRRs, activating cytokines) ▪ Increased expression of Fc receptors for IgE, increased granule production ▪ Some mast cells can be induced to express HLA-2 and present antigen if activation is strong enough 3. A stimulus causes degranulation, resulting in an acute response ▪ See previous slide for acute response – responsible for many signs and symptoms of atopic dermatitis, allergic rhinitis (hay fever) ▪ If this happens over and over, chronic type II inflammation can result 4. Over time, one of three options: ▪ Full resolution and tissue resumes normal appearance and function ▪ Mast cells express “pro-fibrotic” growth factors → repair or fibrosis ▪ The tissue develops features of Type II inflammation – more very soon How Do We Organize Mast Cell Activity? You’re familiar with the early mediators → correlate them with the early activities pictured here Mast cell factors that stimulate issue remodelling: ▪ typical Th2 cytokines (i.e. IL-4) ▪ TGF- ▪ Growth factors* FGF, PDGF, VEGF Macrophages are important in tissue remodelling – mast cells recruit them (M-CSF, GM-MCSF) * Abbreviations in notes on slide Mast Cells – Wrap-up Mast cells are major players in the network of events known as Type II inflammation (more later) ▪ Atopic dermatitis, allergic rhinitis, asthma, food allergies Mast cells are crucial for the defence against parasites, worms, and venoms (proteases can degrade venom) ▪ Mucous secretion, edema, and even damage to the epithelium can all help to expel these invaders Mice depleted of mast cells don’t live very long – death due to peritoneal invasion of these organisms Mast cells aren’t always “pro-inflammatory” ▪ proteases can degrade cytokines ▪ IL-4 can cause macrophages to secrete cytokines and growth factors that favour tissue repair over inflammation Eosinophils Derived from the myeloid lineage – IL-5 is the major cytokine that induces proliferation and activation Eotaxin (FYI – CCL11) promotes migration from blood into peripheral tissues ▪ Eosinophils are normally found in very low numbers in healthy barrier tissues (i.e. skin, lung mucosa, gut mucosa) ▪ Accumulate during acute inflammation and with chronic type 2 inflammation ▪ Interestingly, also accumulate in many chronic inflammatory lesions that are not thought to be Type 2 in nature – most prominently in atherosclerotic plaques These cells are short-lived cells (days) in most cases Eosinophils - Function Like mast cells, eosinophils can release mediators from pre-formed granules OR produce them on demand Eosinophil granule contents: ▪ Major basic protein – major component of granules Cationic protein (lots of (+)ve charges) that has multiple functions: ▪ Toxic to bacterial and eukaryotic cells – increases membrane permeability ▪ Causes activation, degranulation of mast cells and can activate complement ▪ Eosinophil peroxidase – free radical generator ▪ Cytokines – IL-4, IL-13, TNF- (pro-inflammatory) Can also release IL-10 sometimes (anti-inflammatory) Sometimes over long periods of inflammation, can secrete Th1type cytokines (i.e. IL-12) – note that mast cells can do this as well Eosinophils - Function Like mast cells, eosinophils also have the Fc receptor for IgE ▪ Therefore secreted IgE that enters the tissues can activate eosinophils, causing their degranulation How eosinophils and mast cells “use” IgE is somewhat different ▪ Mast cells live for long periods in connective tissue – they “grab” IgE out of the circulation and “hold it”, waiting to detect an allergen or microbe ▪ Eosinophils only migrate into a tissue when they are “called in” during an inflammatory stimulus Once they’re arrived, high levels of IgE will bind to the Fc receptor and then the eosinophil will detect the pathogen/allergen Can eosinophil Fc receptors recognize IgE already bound to antigen? Unsure, maybe. Eosinophils – 2nd (or third?) responders Eosinophils do not enter the barrier immune response until “called in”and activated – usually by a basophil or another cell that secretes eotaxin or IL-5 Histamine Heparin Proteases IL-4, TNF-alpha Innate Lymphoid Cells Three major types of innate lymphoid cells (ILCs): ▪ NK cells – already discussed as a cytotoxic monitor of and responder to abnormal-looking or stressed cells ▪ “Resident” ILCs – these cells live in barrier tissues Type 1 ILCs (ILC1) → secrete cytokines such as IFN- and TNF- → “pushes” the barrier into a “Type 1” response and favours the development of Th1 cells Type 2 ILCs (ILC2) → secrete cytokines such as IL-4, IL-5, IL-9, IL-13 → “pushes” the barrier into a “Type 2” response and favours the development of Th2 cells Type 3 ILCs (ILC3) → secrete IL-17, IFN- → effective against extracellular bacteria, also contribute to lymphoid tissue development at the barrier ▪ NKT cells – not be discussed here Innate Lymphoid Cells ILCs are derived from the lymphoid lineage (not myeloid) ▪ However, ILCs do not express unique, “genetically shuffled” Tcell or B-cell receptors They don’t have many (if any) pattern-recognition receptors (PRR) So what activates them? ▪ For ILC1 cells, it’s the presence of IL-12… very similar to how Th1 cells are activated (but is not antigen dependent, no costimulators, etc.) ▪ For ILC2 cells – what we’ll focus on today – it’s the generation of alarmins ▪ Both also seem to need IL-2 remember IL-2 is an important mitogen/activator for T-cells secreted by Th What’s an alarmin? When PRRs are activated by the epithelial cells of barrier tissues, alarmins are often released ▪ Basically, early-release cytokines from the cells at the border of the inside and outside world ▪ Alarmins typically elicit Th2 responses ILC2 alarmins: ▪ IL-25 ▪ IL-33 ▪ TSLP TSLP = thymic stromal lymphopoietin Together IL-25, IL-33, and TSLP “push” a barrier tissue towards secretion of Th2-type cytokines Rerknimitr, P., Otsuka, A., Nakashima, C. et al. The etiopathogenesis of atopic dermatitis: barrier disruption, immunological derangement, and pruritus. Inflamm Regener 37, 14 (2017). https://doi.org/10.1186/s41232-017-0044-7 Epithelial Cells and Barrier Immunity – the Skin Keratinocytes – water-proof barrier (remember filaggrin) that prevents movement of antigens/microbes (remember tight junctions) into the dermis ▪ Also secrete antimicrobial proteins – psoriasin (chemotactic for leukocytes) and cathelicidins (antimicrobial and chemotactic) in particular Langerhans cells – specialized dendritic cells found in the epidermis that extend processes between keratinocytes ▪ sample the epidermal environment using a variety of PRRs, also present antigens via HLA-2 ▪ Langerhans cells migrate widely – they have been found in mesenteric lymph nodes, presenting antigens The Skin – An Immunology View More lymphocytes tend to be found in the dermis than in the epidermis All three types of ILC are found, as well as resident macrophages, within the dermis Filaggrins and tight junctions are key in limiting the penetration of antigens/microbes into the dermis An Immunology Overview – The Respiratory Tract An Overview – The Respiratory Tract For the previous slide, note: ▪ The type of microbe that activates various ILC-cells ▪ The detector of the microbe ▪ The cytokine/alarmin that stimulates secretion of cytokines from ILCs ▪ The impact of ILC cytokines on immune responses Focus is more on ILC2 cells for today – note how this information relates to the same pathways as your atopic dermatitis case! ▪ ILC1 cells are fair game too, though Secondary Lymphoid Tissue – Skin and Upper Respiratory Tract NALT – nasalassociated lymphoid tissue ▪ Tonsils and adenoids ▪ These are major sites of Th polarization and antibody production in URTIs Lymphoid follicles can also be found be found in the lamina propria of the mucosa (smaller, not as organized as NALT) ▪ Can also be a site of Th polarization and antigen delivery Secondary Lymphoid Tissue – Skin and Upper Respiratory Tract SALT – skinassociated lymphatic tissue… that’s just those palpable lymph notes you can feel outside the ones associated with the neck There are no lymphoid follicles, since there is no lamina propria in the skin Applied Barrier Immunology – Atopic Dermatitis Many patients have defects in barrier proteins ▪ Most common – filaggrin abnormalities ▪ Next most common – abnormalities in claudins (tight junctions) ▪ 20% or more cases of AD can be attributed to defects in barrier proteins ▪ Interestingly, patients with defects in barrier proteins are significantly more likely to develop other allergic diseases later Food allergies, allergic rhinitis Some show particular genetic polymorphisms in Th2related cytokines (i.e. IL-4 or its receptor) Most patients have no clear genetic risk factors ▪ Many of these will still have a prominent family history of atopic disease, though Applied Barrier Immunology – Atopic Dermatitis Some patients with atopic dermatitis do not activate Th2 responses – instead they activate Th17 responses in the skin ▪ Often the skin features more hyperkeratosis, and there is no increase in IgE secretion ▪ Chronic Th2 responses can also result in a “co-existence” of Th17 and Th2 responses/cytokines ▪ More knowledge is being developed here – the signaling is less clear than in Th2 responses Applied Barrier Immunology – Atopic Dermatitis Langerhans cells in particular are good at causing Th cells to become polarized to Th2 cells when they migrate to secondary lymphatic organs (SLOs) ▪ The costimulator that seems to induce Th2 development is OX40-OX40L interaction between the Langerhans cell and the naïve Th cell ▪ TSLP seems to drive the expression of OX40 in the dendritic cell ▪ The Th cell is further “pushed” into a Th2 pathway when it migrates to the inflamed skin and encounters IL-4, IL5, IL-13 ▪ ILC2s produce lots of these cytokines in the presence of alarmins Why Does Atopic Dermatitis Itch So Much? Itching will of course contribute to damaging the skin barrier → loss of moisture ▪ This dryness, damage and the release of alarmins seems to somehow increase neuronal sprouting of pain/itch Cfibres within the dermis and epidermis ▪ This problem is compounded when filaggrin and claudin abnormalities are present Histamine, TSLP, and some Th2 cytokines also seem to contribute to the itching sensation Upper Respiratory Tract Infection – Influenza at the Barrier Influenza invades the respiratory epithelial cell by binding to the glycocalyx ▪ Influenza is endocytosed… and now you have an URTI. What happened? 1. Epithelial cells and dendritic cells detect influenza via TLR7 (viral RNA) and RIG-like receptors ▪ IL-1, IL-23 released → activation of ILC1 cells ▪ Type I IFNs released → activation of NK cells 2. Early response → NK cells recognized the flu particle’s hemagglutinin particles on the cell membrane OR stress molecules on the membrane → killing of respiratory epithelium ▪ Later → NK cells and dendritic cells (or other APCs) are activated by PRRs → release of IL-12 in SLOs Upper Respiratory Tract Infection – Influenza at the Barrier 3. Later response → NK cells and dendritic cells (or other APCs) are activated by PRRs → release of IL-12 in SLOs to naïve Th 4. Th is polarized to Th1 → ▪ Secretion of IFN-y → activation of macrophages Macrophages will continue to be activated in the epithelium due to secretion of IFN-y by ILC1 and any local Th cells ▪ Activation of CD8+ lymphocytes → migration of Tc to the inflamed upper respiratory tract How do cytotoxic T-cells help us clear viruses? Upper Respiratory Tract Infection – Influenza at the Barrier Note as well that Type 1 inflammation (illustrated below) can also result in expression of IL-23 by a wide variety of cells ▪ This leads to activation of ILC3 and Th17 cells (eventually) which can aid AMP secretion and recruitment of neutrophils