The immune system Flashcards
Name cells of the immune system which are of lymphoid linage?
- Lymphocytes (both t and b lymphocytes).
How do lymphocytes recognise antigens?
- Either by B cell or T cell receptors.
In the early stages of inflammation what order do you normally get cells of the immune system?
- Neutrophils, monocytes and then lymphocytes.
Cells of lymphoid origin have how many nucleus?
- They are mononuclear (1).
Cells of myeloid origin usually have how many nucleus?
- Either mononuclear (1) or polymorphonuclear.
What are the main functions of NK (lymphoid in origin) cells and CD8+ T cells?
- Cytotoxicity.
What are the main functions of CD4 + T cells and gamma delta T cells (lymphoid in origin)?
- Regulation of immune response.
What are the main functions of B cells?
- Involved in antibody production and antigen presentation.
What is the main function of dendritic cells?
- Involved in antigen presentation.
What are the main functions of monocytes and macrophages?
- They are involved in antigen presentation but their main function is phagocytosis and killing.
What are the main functions of neutrophils?
- Phagocytosis and killing.
What are the main functions of eosinophils?
- Extracellular digestion.
What are the main functions of basophils and mast cells?
- Inflammation.
Where do cells of the lymphoid and myeloid linage stem from?
- The haematopoietic stem cell.
Give an example of a mononuclear myeloid cell?
- Macrophage and dendritic cells.
Where are immature and mature dendritic cells found?
- Immature: peripheral sites.
- Mature: lymph nodes.
Name some polymorphonuclear (granulocytes) myeloid cells?
- This means they have lobed nucleuses (E.g. neutrophils, eosinophils).
Activated B cells are known as what?
- Plasma cells.
What are natural killer cells?
- Like cytotoxic T cells, contain lytic granules inside the cell that can kill virally infected cells.
What happens when MHC class 1 gets presented to a cytotoxic cd8 T cell?
- Cell is killed.
What happens if a pathogen is presented by MHC class 2 and interacts with cd4 helper T cell?
- This helps regulate the immune response and generate the most appropriate immune response.
How do B lymphocytes respond to the presence of an antigen?
- Recognise antigen via B cell receptor on surface of cells.
- They can recognise antigen in native form doesn’t need to be presented.
- B cell becomes activated to become plasma cell whose main function is to produce antibodies which can then kill those extracellular pathogens.p
What is the T cell receptor composed of?
- Alpha chain and beta chain, small minority can also express a gamma-delta T cell.
Name cells of the immune system which are of myeloid linage?
- Neutrophil, eosinophil, basophil and monocyte.
What are the four classes of pathogen that the immune system protects against?
- Bacteria, viruses, fungi and parasites (can be split into protozoa and worms).
What is a pathogen?
- Any organism with the potential to cause disease.
Give an example of a bacteria?
- Salmonella: causes food poisoning.
Give an example of a virus?
- HIV: causes AIDS.
Give an example of a fungi?
- Candida: causes thrush.
Give an example of a parasite?
- Protozoa: e.g. Leishman causes leishmaniasis.
- Worms: e.g. Schistosoma causes schistosomiasis.
Name the pathogens from largest to smallest.
- Worms (large) -> Protozoa -> fungi -> bacteria -> viruses (small).
What are the two main stages of immune response to infection?
- Recognition: locate and identify invader.
- Defence: repel or destroy the invader (pathogen).
What are the fundamental features of the immune system?
- has to have specificity.
- memory.
- self discrimination.
What is the bodies first line of defence against infections?
- Skin and mucosal surfaces.
What are the routes of infection?
- via airways (inhaled droplets/spores).
- via GI tract (contaminated water and food).
- via reproductive tract (physical contact).
- via external epithelium (physical contact).
- via wounds/abrasions (puncture/damage skin).
- via insect bites.
What are the two types of defence?
- Innate immune responses and adaptive (or acquired) immune responses.
What are the different stages of immune responses?
- 1st innate immunity (occurs immediately 0-4h). Infection - recognition performed by preformed non specific effectors (complement) can get removal of infectious agents.
- early induced response (4-96 hours “early”). Infection - recognition of PAMPs, inflammation recruitment and activation of effector cells - removal of infectious (if not successful adaptive response occurs later).
- adaptive immune response (late: >96h). Infection - transport of antigen to lymphoid organs, recognition by naive t and B cells, clonal expansion and differentiation to effector cells, removal of infectious agents.
What are the stages of the primary immune response?
- epithelial barrier.
- wound.
- early induced response.
- later adaptive response.
What are the main cells in the adaptive immune response?
- B and T cells.
What are the two types of recognition molecules on B and T lymphocytes?
- B cells: B cell receptor/immunoglobulin (Ig).
- T cells: T cell receptor (TCR).
What are lymphocytes?
- Immunocompetent cells of immune system.
They have the ability to recognise and respond to a wide range of antigens.
Describe a B cell receptor.
- 2 identical heavy chains (50-70KDa).
- 2 identical light chains (25KDa).
- pair of identical binding sites for antigen (composed of variable domain from heavy chain and variable domain from light chain).
What are the five classes of immunoglobulin?
- IgG, IgM, IgA, IgD, IgE.
Describe the T cell receptor.
- Made up of 2 polypeptide chains, an alpha and a beta chain.
- Each chain has a constant domain and a variable domain.
- A small number of T cells can express a gamma delta receptor (expressed in a majority of cells).
How many antigen combining sites do T and B cell receptors have?
- B cell: 2 antigen combining sites on B cell receptor.
- T cell: 1 antigen combining site on T cell receptor.
What antigens do T and B cells recognise?
- T cells: T cell receptors only recognise antigens which have been processed and presented by either MHC class 1 or MHC class 2 (t cell becomes activated and becomes an effector T cell producing things like cytokines).
- B cells: recognise antigen in native form, once bound becomes activated and becomes a plasma cell (who’s main function is to produce antibodies).
What are the forms of T cell and how are they presented?
- Cd8+ cytotoxic T cell and is presented by MHC class 1.
- Cd4+ helper T cells and is presented by MHC class 2.
What is MHC class 1 composed of?
- Beta 2 microglobulin and alpha 1, 2, 3 (antigen is presented by alpha 1 and 2 domains).
What is MHC class 2 composed of?
- Alpha 1 and 2, beta 1 and 2 (antigen is presented by alpha 1 and 2).
What are the 2 primary lymphoid organs?
- Thymus and bone marrow (lymphocytes arise from stem cell progenitors in the bone marrow).
Where do B and T cells mature?
- B cells complete maturation in the bone marrow whereas T cells leave at the immature stage and complete their development in the thymus.
There are a variety of secondary lymphoid organs, name a few?
- Lymph nodes, spleen, bronchus-associated lymphoid tissues.
Characteristics of lymph node?
- Small kidney shaped organ, around 1-2cm long, carefully packed with lymphocytes, macrophages and other cells of the immune system.
- T cells in inner cortex B cells in outer cortex.
Characteristics of the spleen?
- Large lymphoid organ found in the upper left hand side of the abdomen.
- Red pulp area: old or damaged cells removed from circulation.
- White pulp area: tissue in which lymphocytes respond to pathogens.
- Periarteriolar lymphoid sheath (PALS) mainly contains t-cells.
- Lymphoid follicle: mainly contains B cells and macrophages.
- Like lymph node B and T cells found in anatomically discrete areas.
Characteristics of gut associated lymphoid tissue (GALT)?
- B cells when activated generate germinal centres.
- B cell rich areas and T cell rich areas.
- The m cell delivers the pathogen from lumeral side of gut closer to the lymphoid tissues.
- In GALT T and B cells become activated when pathogen crosses m cell - they leave via efferent lymphatics to go back into blood circulation.
If pathogens are going to be recognised by T lymphocyte (T cell) they have to be processed and presented by what?
- either MHC Class 1 or MHC Class 2.
Explain B cell development.
- takes place in bone marrow.
- earliest B cells interact with stromal reticular cells where they proliferate and mature.
- cell selection occurs and apoptotic cells are phagocytosed by macrophages any cells that do not survive and therefore removed.
- cells that survive interact with these adventitial reticular cells which facilitate exit out of bone marrow and into circulation.
Explain T cell differentiation in the thymus.
- start off with T cell which doesn’t express any cd4 or cd8, it enters thymus via blood vessel and starts to express and rearrange its T cell receptor and interacts with corticol epithelial cells which express MHC.
- if it doesn’t recognise self MHC it gets removed (apoptosis).
- if it does but also recognises self antigen cell is also removed.
- if it recognises MHC but not self antigen, cell leaves and enters cortiomedullary region still cd4 and cd8 +ve and its only when it reaches the medulla that it decides if it’s a cd4 or cd8 cell.
- these cells then leave as naive T cells all which express lots of T cell receptor.
Where do T cells and B cells congregate in the lymph nodes?
- T cells congregate in inner cortex.
- B cells congregate in outer cortex.
