Mucosal Immunity Flashcards by Ethan Tennant

Describe the structure of an antibody

A Y-shaped structure consisting of 4 polypeptides

2 heavy chains, 2 short chains
With disulfide bonds between the chains
2 Antigen binding sites

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What is agglutination and why can it occur?

Agglutination is the clumping of bacteria

-can happen as an antibody has 2 antigen-binding sites

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What are immunoglobulins?

Antibodies

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How many classes of immunoglobulins are there and what makes the classes different?

There are 5 classes of immunoglobulins 
-each class has a different heavy chain constant region

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What is immunoglobulin class switching?

It is also known as isotopic switching

-It is the biological mechanism that changes a B cells production of immunoglobulin from one type to another

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What are the 5 different types of immunoglobulins?

IgA-secreted at mucosal sites
IgD- B cell receptor
IgE-parasite responses and allergies
IgG-multi-purpose, high affinity and crosses the placenta
IgM- first to be made on first encounter with antigen

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How are B cells activated?

Via 3 signals:

from the antigen binding to the BCR
Co-stimulation frm a helper T cell
Cytokines from a helper T cell (cause class switching)

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How do cytokines regulate expression of antibody classes?

As which ever cytokine the helper T cell secretes causes class switching and determines which antibody the B cell produces

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What are the subclasses of immunoglobulins?

IgG- IgG1, IgG2, IgG3, IgG4
IgA- IgA1, IgA2

-IgM, IgD and IgE dont have subclasses

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What is the effect of IL-4 on antibody class expression?

Inhibits: IgM, IgG3, IgG2a
Induces: IgG1, IgE

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What is the effect of IL-5 on antibody class expression?

Increases production of IgA

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What is the effect of IFN-gamma on antibody class expression?

Inhibits: IgM, IgG1, IgE
Induces: IgG3, IgG2a

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What is the effect of TGF-beta on antibody class expression?

Inhibits: IgM, IgG3
Induces: IgG2b, IgA

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What is the effect of IL-21 on antibody class expression?

Induces: IgG3, IgG1, IgA

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What are the 3 main functions of antibodies?

Neutralisation
Opsonisation
Complement activation

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How do antibodies neutralise pathogens?

Antibodies bind bacterial toxins and virus particles

- This stops them binding receptors on the cells and prevents damage to tissue

What is opsonisation?

Antibodies coating dangerous antigens in opsonins, which promote phagocytosis

How do antibodies cause NK cell sensitisation?

IgG Antibodies binds antigen on the surface of target cells
Fc receptors on NK cells recognise bound antibody
Cross linking of Fc receptors signals the NK cell to kill the target cell by apoptosis

How do antibodies cause mast cell, eosinophil and basophil sensitisation?

IgE binds to Fc receptors on mast cells, causing the mast cell to degranulate releasing histamine
Eosinophils recognise IgE bound to parasites and release granules to kill the parasite
Soluble IgD binds to basophils activating antimicrobial and proinflammatory mechanisms

What is the function of lymph nodes in immunity?

Entrap pathogens/ antigens entering the lymphatic system from tissues
-packed with lymphocytes, macrophages and dendritic cells

Describe how the lymph nodes process foriegn antigens?

Antigen and APC from tissue travel to lymph node via lymphatic fluid
Processed by dendritic cells in paracortex
Specific helper T cells activated
B cells activated in primary follicle
Leads to production of a secondary follicle, germinal centre and antibody producing plasma cells

What is clonal selection and expansion of activated B cells?

Clonal selection- how a single B cell that recognises an antigen that enters the body is selected from a pool of different antigen specificities
Clonal expansion- many copies of that specific B cell are produced with the shared affinity and specificity of the antigen

What is the function of the spleen?

Functions as a fliter for blood

-not supplied by lymphatic vessels therefore spleen responds to systemic infections

What are the 2 distinct regions of the spleen and how are they seperated?

Red pulp and white pulp

-seperated by a diffuse marginal zone

What does the red pulp of the spleen contain?

Contains mainly macrophages, red blood cells with few lymphocytes

What does the white pulp of the spleen contain and what does it surround?

Predominantly populated by T cells | - the white pulp mainly surrounds the arteries in the slpeen, forming a periarteriolar lymphoid sheath (PALS)

Describe how the spleen processes foreign antigens?

- Foriegn antigen carried into the spleen from the splenic artery into marginal zone where it is captured by dendritic cells - In the PALS dendritic cells activate helper T cells - Active helper T cells activates B cells - Leads to production of a secondary follicle with germinal centre

What is a germinal centre?

Germinal centres are a specialised enviroment for B cell proliferation and somatic hypermutation

What is the structure of a germinal centre?

Contains a mantle zone around the edges | Inside there is a light and a dark zone

What is somatic hypermutation?

A way of introducing increased antibody diversity | -introduces point mutations in the variable region of DNA at a very high rate

What is the process of somatic hypermutation in a germinal cell?

- Somatic hypermutation happens in the dark zone of the germinal centre - Selection of survival in light zone - Cells with disadvantageous BCR mutations killed through apoptosis - Cells with advantageous BCR mutations (e.g increased affinity) move further into the light zone - Recieve signal from helper T cells to differentate into plasma or memory B cells (can induce class switching)

What are MALTS?

Mucosa Associated Lymphoid Tissue | -they defend the body agaisnt pathogen entry via the mucous membranes

What are the 2 main types of MALTS?

BALTS- Bronchus-Associated Lymphoid Tissue | GALTS- Gut-Associated Lymphoid Tissue

What structures fall under GALTS?

``` Peyer's Patches (small intestine only) Isolated Lymphoid follicles (throughout the intestine) Appendix Palatine tonsils Adenoid glands Lingual tonsils ```

What are tonsils and what is their function?

Tonsils are nodular structures with a meshwork of reticular cells, macrophages, granulocytes and mast cells - contains follicles and germinal centres - functions in the defence against antigens entering the nasal and oral epithelia

What are peyers patches and what are their function?

Comprised of 30-40 nodules in outer wall of the small intestine The nodules contain follicles which will develop germinal centres on antigen exposure

What are M cells and what is their function?

Microfold cells are intestinal epithelium cells that sample and transport pathogen/antigens from the luminal surface to the sub-epithelium (transcytosis)