Week 0 - Immune Intro Flashcards
What are the 2 soluble factors in the innate immunity?
- Antibacterial factors
2. Complement system
What is the cellular factor of the innate immunity?
Scavenger Phagocytes
What is a lysozyme?
Enzyme present at mucosal surfaces that breaks down the gram positive cell wall
What does lactoferrin do (protein found at mucosal surfaces)?
- Chelates iron & reduces soluble iron in the GI/respiratory tract
- Inhibits growth of bacteria
What are the 3 pathways in the complement system of innate immunity?
- Classical Pathway
- MB-Lectin Pathway
- Alternative Pathway
Describe the classical pathway of the complement system?
Antigen : Antibody complexes
Describe the MB-Lectin Pathway of the complement system?
Lectin binding to pathogen surfaces
Describe the Alternative pathway of the complement system?
Activated through pathogen surfaces
What 3 things does complement activation do?
- Recruit inflammatory cells
- Opsonization of pathogens
- Killing of pathogens
What does MB-Lectin stand for?
Mannose-binding lectin
What are the 2 key roles of macrophages?
- Clearance of micro-organisms
2. Summon help (releasing cytokines)
What is the difference between monocytes and macrophages?
- Monocyte= blood
- Macrophages= tissue
Describe phagocytosis?
- Specialises in destruction of pathogens
- Removes harmless debris
Describe antigen presentation?
Processes engulfed particles, travels to draining lymph nodes & presents to T cells in MHC II
What 3 things are pattern recognition receptors able to do?
- Recognise molecules found in micro-organisms
- Recognise extracellular & intracellular threats
- Respond to bacteria, fungi and yeasts
Why is the immune system not enough at times?
- Highly pathogenic bacteria
2. Structural failure
What % of neutrophils are in white blood cells?
50-70%
Neutrophils provide a _____ response to infection?
Rapid
What are the 4 factors of neutrophils?
- Chemotaxis
- Phagocytic
- Degranulation
- Die locally
Describe neutrophil chemotaxis?
Migrate towards bacterial products (LPS), chemokines & “danger signals” (complement components)
Describe neutrophil phagocytosis?
Ingest & destroy pathogens using proteases, reactive oxygen species, lysozyme etc.
Describe neutrophil degranulation?
Release toxic granules extracellularly
Describe how neutrophils die locally?
By producing characteristic pus
Eosinophils have a pathological role in _____?
Allergy
What are the 3 factors of eosinophils?
- Chemotaxis
- Degranulation
- Cytokine production
Describe eosinophil degranulation?
Release toxic substances onto surface of parasites e.g. Major Basic Protein, Eosinophil Cationic Protein, Eosinophil Peroxidase
What does eosinophils classically respond to?
Parasites
What is the difference between basophils and mast cells?
- Basophils= blood
- Mast cells= tissues
What are basophils/mast cells important in?
Allergy
What are the 2 factors of Basophils/Mast cells?
- Degranulation
2. Cytokine release
Describe Basophil/Mast cell degranulation?
Rapid release pre-formed granules containing cytokines & mediators
What is the typical reaction caused by basophils/mast cell degranulation?
Histamine Wheal & Flare reaction
What are the 3 factors of dendritic cells?
- Phagocytosis
- Migration
- Antigen presentation
Describe dendritic cell phagocytosis?
- Not specialised in destruction of pathogens
- Functions mainly as antigen presenting cells
Describe dendritic cell migration?
- In tissues constantly sampling environment
- When activated will travel to draining lymph nodes
Describe dendritic cell antigen presentation?
Presents to CD4 T cells & can initiate an adaptive immune response
What are the 2 types of adaptive immunity?
- Humoral
2. Cellular
What is the humoral adaptive immunity mediated by?
B cells
What does the B cells do in humoral adaptive immunity?
Release antibodies (immunoglobulins) which targets extracellular pathogens ie. bacteria
What 2 things mediate the cellular adaptive immunity?
- CD4 T cells
2. CD8 T cells
What do the CD4 T cells in the cellular adaptive immunity do?
- Directs B cells & CD8 T cells
- Cytokine secretion
What are CD4 T cells also known as?
“Helper” T cells
What are DC8 T cells also known as?
“Killer” or “Cytotoxic” T cells
Describe the 2 regions on an antibody?
- Fab region: antigen binding
- Fc region: binds to Fc receptors on phagocytes & activates complement
What are the 3 functions of antibodies?
- Opsonise for phagocytosis
- Activate complement for lysis
- Neutralise toxins & pathogen binding sites
Describe IgM?
- Main antibody of primary immune response
- Low affinity
- Activates Complement
Describe IgG?
- Main antibody of secondary immune response
- Higher affinity as part of secondary response
- Activates Complement, binds Fcg receptor on phagocytes (opsonsises)
- Crosses placenta
Describe IgA?
- Present in secretions & lines epithelial surfaces
- Neutralises by blocking binding of pathogens
Describe IgE?
- High affinity binding to Mast cells through Fc receptor
- Role in allergy
The antibody isotopes differ in ______?
Fc regions
Describe the primary B cell response?
- 5-10 days
- Smaller peak
- IgM>IgG
Describe the secondary B cell response?
- 1-3 days
- Larger peak
- Increase in IgG & sometimes IgA / IgE
List the 5 things that T cells can encourage in the immune system response?
- Clonal expansion of specific B cells
- Progression to antibody secreting cells (plasma cells)
- Progression to memory B cells
- Isotype switching to IgG, IgA & IgE
- Affinity Maturation
Where are B cells developed?
Bone marrow
How do B cells die?
If B cell receptor binds strongly to “self” antigen in bone marrow it dies by apoptosis
Where are T cells developed?
Bone marrow and migrate to thymus
How do T cells die?
If T cell receptor binds strongly to “self” antigen in thymus it dies by apoptosis
T cells only see antigen in context of ____?
MHC
Describe Class I MHC?
- Presents to CD8 T Cells
- Found on all nucleated cells
- Presents intra-cellular antigen
Describe Class II MHC?
- Presents to CD4 T Cells
- Presents extra-cellular derived antigen (phagocytosed)
- Found on Antigen Presenting Cells
List 3 antigen presenting cells?
- Dendritic cells
- Macrophages
- B cells
What are the 2 primary organs of the adaptive immune system?
- Thymus
2. Bone marrow
What are the 3 secondary organs of the adaptive immune system?
- Lymph nodes
- Spleen
- Mucosal Associated Lymphoid Tissue of GI Tract (MALT) & Bronchial Tract (BALT)
What is the function of the spleen?
Filters blood of senescent cells &
blood borne pathogens
List the 4 functions of the adaptive immune system?
- Provides specific antibodies to innate immune system, enhancing pathogen clearance
- Provides cytokines to innate immune system to upregulate activity
- Finishes off clearing pathogens
- Develops memory to prevent future infection
List the 5 immune cells in the secondary immune response?
- Memory B cells
- Memory T cells
- Memory lymphocytes
- Preformed antigen specific IgA
- Preformed high affinity IgG
Describe the role of memory lymphocytes in the secondary immune response?
Have lower threshold for activation & actively patrol sites of previous pathogen entry
What happens to B cells in an immune response?
Enters lymphoid follicle to form germinal centre & undergo affinity maturation
What is the classification framework called for the adaptive immune system?
Coombes and Gell Classification
Describe type I hypersensitivity response?
- Immediate, atopic
- IgE mediated bound to mast cells
- Increase in severity with repeated challenge
Describe type II hypersensitivity response?
- Cytotoxic, antibody dependent
- IgM or IgG bound to cell/matrix antigen
- Uncommon cause of allergy
Describe type III hypersensitivity response?
- Immune complex
- IgM or IgG bound to soluble antigen
- Aggregate in small blood vessels
Describe type IV hypersensitivity response?
- Mediated by action of lymphocytes infiltrating area
- T cells (CD4+ & CD8+)
What is type I hypersensitivity responsible for?
Most allergies
List the 6 stages of type I hypersensitivity/ an allergic response?
- Sensitisation
- Mast cells primed with IgE
- Re-exposure to antigen
- Antigen binds to IgE associated with mast cells
- Mast cells degranulate
- Pro-imflammatory process stimulates and amplifies future responses
List 6 things that mast cells release when degranulating in an allergic response?
- Toxins (i.e. histamine)
- Tryptase
- Pro-inflammatory cytokines
- Chemokines
- Prostaglandins
- Leukotrienes
What 2 things does the early phase tissue effects in type I hypersensitivity result in?
- Smooth muscle contraction
2. Increased vascular permeability
What 2 things does the late phase tissue effects in type I hypersensitive result in?
- Sustained smooth muscle contraction/ hypertrophy
2. Tissue remodelling
What is anaphylaxis?
Severe, systemic type I hypersensitivity
Describe anaphylaxis?
- Widespread mast cell degranulation caused by systemic exposure to antigen
- Vascular permeability is principle immediate danger:
ie. Soft tissue swelling threatening airway, loss of circulatory volume causing shock
What is type II hypersensitivity a common cause of?
Autoimmune disease
List the 3 stages of type II hypersensitivity?
- Sensitisation
- Opsonisation of cells
- Cytotoxicity: Complement activation, inflammation, tissue destruction
What can happen in some cases of type II hypersensitivity?
Direct biological activation with antigen (i.e. receptor activation, impaired enzyme action)
What 2 things is type III hypersensitivity a cause of?
- Autoimmune disease
2. Drug allergy
What 3 things can happen due to type III hypersensitivity aggregating in small blood vessels?
- Direct occlusion
- Complement activation
- Perivascular inflammation
What is type IV hypersensitivity also known as?
Delayed type hypersensitivity
Give an example of type IV hypersensitivity?
Dermatitis
What is the exception for autoimmune disease?
Autoimmune diseases which fit into a single category of hypersensitivity
What is the definition of an autoimmune disease?
Harmful inflammatory response directed against ‘self’ tissue by the adaptive immune response
Describe type I diabetes?
Selective, autoimmune destruction of the pancreatic β-cells
What type of hypersensitive is type I diabetes?
Often mix of Type II & Type IV
What precedes symptoms of type I diabetes?
Inflammation of the Islets of Langerhans
Describe Myasthenia Gravis?
Syndrome of fatigable muscle weakness (limbs, respiratory, head & neck)
What is Myasthenia Gravis caused by?
IgG against acetylcholine receptor which therefore prevents signal transduction
List 5 examples of systemic autoimmune disease?
- Rheumatoid arthritis
- Systemic lupus erythematosus
- Inflammatory bowel disease
- Connective tissue disease
- Systemic vasculitis
List the signs and symptoms of rheumatoid arthritis?
- Pulmonary nodules & fibrosis
- Pericarditis & valvular inflammation
- Small vessel vasculitis
- Soft tissue nodules
- Skin inflammation
- Weight loss, anaemia
Describe the pathophysiology of rheumatoid factor?
- IgM & IgA directed against IgG Fc region
- Forms large immune complexes
Where are the large immune complexes in rheumatoid factor located?
- High conc in synovial fluid
- Also found in other tissues
Describe the pathophysiology of rheumatoid arthritis?
- Inflammation = release of PAD from inflammatory cells
- Further chemoatraction of inflammatory cells into synovium
- Osteoclast activation & joint destruction
- Fibroblast activation & synovial hyperplasia
What is common in rheumatoid arthritis?
Anti-citrullinated protein/ peptide antibodies
What does PAD do?
Alters variety of proteins by converting alanine –> citrulline
What 3 inflammatory cells are sent into the synovium during rheumatoid arthritis?
- Macrophages
- Neutrophils
- Lymphocytes
What are the 3 means of treatment for autoimmune diseases?
- Steroids
- Inhibitors of metabolism
- Inhibitors of T-cell function
What are biologic therapies?
Therapeutic agents synthesised biologically rather than chemically
What is the nature of biologic agent Infliximab & what is its target?
- NATURE: monoclonal antibody
- TARGET: soluble cytokine
What is the nature of biologic agent Etanercept & what is its target?
- NATURE: soluble receptor
- TARGET: soluble cytokine
What is the nature of biologic agent Rituximab & what is its target?
- NATURE: monoclonal antibody
- TARGET: surface marker
List 3 examples of biologic therapies?
- Infliximab
- Etanercept
- Rituximab
What are the 3 benefits of biologic therapies for treating rheumatoid arthritis?
- Reduces joint swelling & pain
- Decreases systemic inflammation
- Delays & prevents appearance of erosions & bone deformity
What is the risk of biologic therapies for treating rheumatoid arthritis?
Increased risk of infection especially TB
What can biologic therapeutics turn off in the during the inflammatory reaction in rheumatoid arthritis?
TNF-alpha
List the 3 environmental factors which can lead to autoimmune diseases?
- Infection
- Geographical factors
- Modifiable personal risk factors
Give 2 examples of how infection can be a factor for autoimmune disease?
- Molecular mimicry
2. Tissue damage exposing self-antigens
Give an example of a geographical factor which can lead to autoimmune disease?
Vit D deficiency
Give an example of a modifiable personal risk factor which could lead to autoimmune disease?
Smoking
What autoimmune disease is a deficiency in Vit D associated with?
Multiple Sclerosis
How is smoking associated with rheumatoid arthritis?
Smoking is associated with conversion of alanine to citrulline
What are the 2 different types of autoimmune diseases?
- Organ specific
2. Systemic