Principles of immune response Flashcards Preview

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Flashcards in Principles of immune response Deck (36):
1

Functions of immune responses

- Protection of host from pathogenic microorganisms
- Distinguishing self from non-self
- Distinguishing self from abnormal self (cancerous cells)

2

Principles of immune responses

- Activation requires recognition of danger signals.
- Encountering a pathogen causes formation of specific antibodies
- This leads to faster, larger, more efficient clearance of pathogen during second exposure
- Highly polymorphic (variable) genes

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Consequences of failure of immune system

This is immunodeficiency, increased infection, increased risk of cancer

4

Definition of autoimmunity

Recognition of self cells as harmful material by immune system

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Definition of allergy/hypersensitivity

Recognition of harmless non-self as harmful

6

Two immune system response INITIATION strategies

Strategy 1 - Pattern Recognition Receptors
Strategy 2 - Antigen-specific receptors on lymphocytes

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Summary of pattern recognition receptor strategy

- Common molecular patterns
- Germline encoded
- Recognise (PAMPs) pathogen associated molecular patterns and (DAMPs) damage associated molecular patterns

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Summary of antigen-specific receptors on lymphocytes used as initiation strategy

- Each antigen receptor binds a specific site (epitope) on an antigen
- Randomly generated through gene recombination in lymphocytes
- Millions of potential different receptors possibly encoded

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Definition of lymphocyte

Type of white blood cell which carries an individual receptor specific to a particular antigen

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Antigen definition

A molecule that is recognised and bound by lymphocytes

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Antibody definition

A soluble receptor specific to an antigen synthesised and secreted by B lymphocytes = Immunoglobulin (Ig)

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Features of innate immunity

- Fast
- Germline encoded, pre-formed components
- Limited specificity to DAMPs/PAMPs
- Independent of previous exposure
- No memory

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What do DAMP and PAMP stand for

- Damage Associated Molecular Pattern
- Pathogen Associated Molecular Pattern

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Cells of innate immunity

Macrophages/monocytes
Neutrophils
Basophils
Eosinophils
Complement
Natural Killer cells
Dendritic cells

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Roles of innate immunity

- Destruction of invading nucleic acids (viruses) in cytoplasm
- Activation of inflammatory pathways and production of antiviral type 1 interferons
- Contain and limit pathogenic spread whist adaptive immune response begins
- Prime and direct appropriate adaptive response

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Features of adaptive immunity

- Slow
- Clonal selection of randomly generated antigen receptors
- Unlimited specificity, can theoretically bind any epitope with high specificity
- Dependent on previous exposures
- Memory (acquired immunity)

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Cells of adaptive immunity

B-lymphocytes
T-lymphocytes

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Roles of adaptive immunity

- Selection and expansion of antigen specific clones
- Targeted elimination of pathogen
- Production of memory cells

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Antigen receptors of B and T cells

B cells - Membrane-bound Immunoglobulin
T cells - T cell receptor

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Process of clonal expansion

- B/T lymphocytes circulate in naive, inactive form
- Encounter complementary antigen, survive and proliferate
- Produces clones of cells which present the same antigen

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Process of clearing infection

- Cytotoxic T cells kill infected cells
- Antibodies activate complement
- Antibodies inactivate toxins directly
- Antibodies activate Natural Killer cells

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Final fates of clonal lymphoctes

- Death by apoptosis
- Survival as memory cells

23

Cytokine definition

A substance which is secreted by certain cells of the immune system and have an effect on other cells

24

Examples of cytokines and their actions

- Interleukins, between WBCs
- Interferons, anti-viral effects
- Chemokines, chemotaxis and movement
- Growth factors, growth and repair
- Cytotoxic, tumour necrosis factor

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Process of cytokine release

- Cytokine-producing cell stimulated
- Cytokines released
- Bind to receptor on target cell
- Signal amplified inside target cell
- Gene activation occurs
- Leads to desired biological effects

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Three mechanisms of cytokine action

Autocrine - act on releasing cell
Paracrine - Act on nearby cell
Endocrine - Act on distant cell, travel by circulation

27

Process of dendritic cell cytokine release

- Network of cells located at likely sites of infection
- Recognise microbial patterns, secrete cytokines
- Capture pathogens and migrate to lymph nodes
- Present antigens to adaptive immune system

28

Definition of complement

A system consisting of a number of small proteins found in the blood, synthesised in the liver, which circulate as inactive pro-proteins

29

Process of complement action

- Stimulation by trigger
- Proteases cleave specific proteins to release cytokines
- Initiates further cascade of further cleavages
- Stimulate phagocyte movement
- Initiate inflammation
- Construction of membrane attack complex

30

Complement activation pathways

Classical pathway - activated by antigen-antibody complex
Alternative pathway - activated by pathogen surfaces
Lectin pathway - Antibody-independent activation of classical pathway, lectins bind to carbohydrates found on pathogens

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Mechanisms of control of complement

- Short half-life of components
- Dilution of components in biological fluids
- Specific regulatory proteins

32

Functions of complement

- Lysis
- Opsonisation
- Activation of inflammatory response
- Chemotaxis

33

Features of acute-phase response

Fever
Increased WBC production
"Acute-phase" protein production in liver

34

Acute phase proteins

C-reactive protein - activates complement
Mannan-binding lectin - activates complement
Complement
Fibrinogen - clotting

35

Role of toll-like receptors

Involved in immune response as a type of pattern recognition receptor

36

Mechanism of toll-like receptors

- Ligands bind and activate receptor
- TLRs recruit proteins in cytosol of immune cell with propagate signal transduction pathway
- Upregulation or suppression of inflammatory response genes
- Bacterial ligand = pathogen phagocytosed, digested, antigens presented to CD4+ T cells
- Viral ligand = infected cell enters apoptosis or release interferons