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MCD - Immunology > Organisation of the immune system > Flashcards

Flashcards in Organisation of the immune system Deck (32)
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Physical barriers for host defence

Skin - mechanical barrier, acidic environment
Mucous membranes - mucus secretions trap microorganisms, cilia expel microorganisms


Physiological barriers for host defence

Body temperature/fever
Low pH in stomach
Chemical mediators - lysosomes, interferons, complement


Cell types of the immune system

T lymphocytes
B lymphocytes
Antigen presenting cells
Mast cells
Dendritic cells
Natural Killer cells


The two major types of T lymphocyte

CD4+ T lymphocytes
CD8+ T lymphocytes


CD4+ T lymphocyte function

T helper cells
Regulatory T cells
- Secrete cytokines


CD8+ T lymphocyte functions

Cytotoxic T cells
- Lyse infected cells
- Secrete cytokines


Process of antigen recognition in T cells

T cells only recognise processed antigen presented at the surface of another cell upon binding with T cell receptor.
Antigen is presented by an MHC molecule after processing.


B lymphocyte features

- Surface antigen receptor is an Immunoglobulin-like structure
- Express MHC class II which present antigen to T helper cells
- Recognised free, intact antigens in body fluids or on cell surfaces
- Use B cell receptor


Role of antigen presenting cells and examples

- Present processed antigens to T lymphocyte to initiate an adaptive immune response
- Dendritic cells
- B lymphocytes
- Macrophages


Roles of neutrophils

Killing of microbes


Roles of eosinophils

Granule release
Defence against parasitic infections


Roles of basophils

Granule release
May act as APC


Roles of monocytes/macrophages

Killing of pathogens
Cytokine release
Acting as APC


Roles of mast cells

Pro-inflammatory granule release
- Secrete histamine and inflammatory mediators such as cytokines
- Can recognise, phagocytose and kill bacteria
- Activation leads to vasodilation and increased vascular permeability


Roles of dendritic cells

Antigen capture
Antigen presentation


Roles of Natural Killer cells

Lysis of infected cells (NOT pathogens)


What are neutrophil extracellular traps

Activated neutrophils release granule proteins and chromatin to form extracellular fibres which trap and immobilise pathogens


Method used to distinguish white blood cells

Cluster of Differentiation
- Uses CD markers
- System differentiates cells based on which antibodies bind to specific molecules expressed on the cell surface


Definition of a primary lymphoid organ

An organ where lymphocytes develop and congregate


Primary lymphoid organs

- Bone marrow, site of B cell maturation and production of immature T cells
- Thymus, site of T cell maturation


Definition of a secondary lymphoid organ

An organ where lymphocytes interact with antigens and other lymphocytes


Secondary lymphoid organs

The spleen
Lymph nodes
Mucosal associated lymphoid tissues (MALT)


Features of the thymus

- Bi-lobed
- Contains whirls of fibroblasts (Hassall's corpuscles) site of T cell development
- Size decreases with age (atrophy)
- T-cell variation output decreases with age but total output number remains the same


Features of bone marrow

- Site of haematopoiesis
- Increases white blood cell output during acute-phase response
- 2 types, Red and Yellow
- Red marrow = haematopoietic tissue
- Yellow marrow = fatty tissue


Functions of the lymphatic system

- Drainage system for extracellular fluid
- Provides sites for immune cells to interact


Features of the spleen

- Red and white pulp
- White pulp contains lymphocytes and carries out active immune response
- Red pulp is primarily a filter for the blood, also site of red cell turnover
- PALS periarterial lymphatic sheath is T cell area
- Primary follicles is B cell area


Features of the mucosa associated lymphoid tissues (MALT)

Lymphoid tissues located near sites of likely infection in the mucosa. Provide defence support to epithelia.


Features of Gut Associated Lymphoid Tissue (GALT)

Organised lymphoid tissue - "Peyer's patches" which contain compartmentalised cells.
Disorganised lymphoid tissue parts are associated with lymph drainage
M-cells sample antigens and transfer them to dendritic cells
Dendritic cells then migrate to Peyer's patch and present the antigens to lymphocytes for clonal expansion


Problems leading to necessity of lymphocyte recirculation

- Very large number of T cells with different specificities
- Very large number of B cells with different specificities
- May only limited amounts of antigen
- Body needs a way of ensuring lymphocyte meets its specific antigen


Lymphocyte recirculation process

- Naive lymphocytes leave bone marrow/thymus and enter bloodstream
- Travel through blood and either find its complementary antigen or dies
- Recirculates through peripheral lymphoid tissues


Fates of lymphocytes in lymphocyte recirculation

- Due by apoptosis
- Recognise antigen, activation of B cells leading to massive B cell proliferation in secondary lymphoid tissue


Process of extravasation (movement from blood vessel into tissue) of naive T cells into lymph nodes

- Rolling, naive T cells 'roll' along epithelium
- Activation, T cells stopped and activated by chemokine at a particular place by selectins
- Arrest and adhesion, integrins increase adhesion of T cell to epithelium leading to arrest of cell
- Transendothelial migration, movement of T cell from epithelial surface into lymph node