Immunity Flashcards
Define pathogen.
An organism with the potential to cause disease.
Define immunity, immune system and immune response.
- the ability to resist disease
- a network of cells, tissues and organs that functions to defend the body against pathogens
- coordinated reaction of immune system
Define antigen.
- Molecules that are recognised by the immune system and can stimulate an immune response.
What precursor cell gives rise to most cells involved in innate response?
common myeloid progenitor
What does common lymphoid progenitor give rise to?
- B and T lymphocytes and NK cells
Which immune cell triggers main characteristics of inflammation?
- Macrophages produce cytokines triggering heat and swelling.
What does the innate immunity involve? (4)
- Rapid response
- Recognises pathogen-associated molecules
- Facilitates the adaptive response (calls for reinforcements)
- Components include: physical barriers (skin, mucus, chemical barriers), proteins (complement, cytokines, chemokines), cells (macrophages, granulocytes)
Describe the 2 forms of adaptive immunity.
- Humoral (liquid/soluble part of body): mediated by antibodies derived from B cells.
- Cellular: mediated by T cells.
Define epitope.
- Only part on antigen that is recognised by lymphocytes.
- A single antigen may have multiple epitopes.
- Each lymphocyte is specific for one epitope
Function of B cells.
- Primary defence against extracellular pathogens.
Function of T cells.
- Primary defence against intracellular pathogens.
What are the primary lymphoid organs and their function?
- Bone marrow (B cells) and thymus (T cells).
- Development and maturation of lumphocytes.
What are the secondary lymphoid organs and their function?
- Spleen, lymph nodes, tonsils, Peyer’s patches, mucosa-associated lymphoid tissue (MALT), appendix
- Where lymphocytes encounter pathogens and become activated.
Where are most lymphocytes found?
- More than 50% are found in lymph nodes and spleen.
Function of the spleen.
- Acts primarily to filter blood and fight infection.
- Largest lymphatic organ
Describe the coordinated response of the immune system.
- Lymphocytes recirculate through lymph node/spleen via blood.
- Antigens/pathogens are funnelled from the periphery into the local lymph nodes.
- Lymphocytes encounter antigen in the secondary lymphoid organs.
How does lysozyme act as a chemical barrier?
- Exposes the lipid bilayer.
How does the immune system detect pathogen?
- Components of innate immunity recognise pathogen-associated molecular patterns (PAMPs) and microbe-associated molecular patterns (MAMPs).
- PAMPs is detected by pattern recognition receptors (PRRs- on cell can express many PRRs).
What are macrophages and their function in immunity? (3)
- Reside in blood (monocyte precursor) and tissues (macrophage)
- Usually the first to encounter pathogen
- Function include phagocytosis, antigen presentation and cytokine production.
Name a few PRRs and describe one. (2)
- Mannose receptor, scavenger receptor, C-type receptor and toll-like recpetors (TLRs)
- TLR-4 recognises lipopolysaccharide (LPS). TLR5 recognises flagellin, TLR 3, 7, 8, 9 recognises internal stranger signals.
Function of NF-kB.
- A protein that controls transcription of DNA, cytokin and or/chemokine production and invovled in inflammatory response.
How does opsonisation enhance phagocytosis? (3)
- Host proteins called opsonins coats the bacteria presenting more markers for phagocytic cell to be able to see/bind to the pathogen and engulf it.
- Opsonins are soluble proteins which bind to pathogens. eg. antibodies (IgG), C3b (complement protein)
- Phagocytic cells express receptors that recognise these molecular tags. eg. FcR (binds antibody) or CR1
Function of cytokine and chemokine.
- Important in producing inflammation, changing permeability of blood vessels and recruiting cells to site of infection.
- Cytokines block viral spread (interferons block transcription/translation), activate other cells (NK cells, macrophage), upregulate MHC molecules
- Chemokines regulate movement of cells and mobilise/recruit immune cells.
What are granulocytes and list some examples?
- Characterised by secretory granules in their cytoplasm and multi-lobed nucleus. eg. neutrophils, eosinophils, basophils
Function of neutrophil. (5)
- Most common white blood cell and is largely stored in bone marrow.
- Mobilised by following concentration gradients of chemotaxins/chemokines (interleukin 8).
- Predominant role is phagocytosis (express PRRs and receptors for complement and antibody (FcR))
- Short lived (die after destroying pathogen- pus)
- Expels sticky strands of DNA (NETs) to capture and kil pathogen.
Function of eosinophils. (4)
- Mainly found in tissues
- Role in anti-parasite immunity (protozoans and helminth worms)
- Contribute to allergic responses
- Triggered to release content of their granules into surrounding area. eg. cytotoxic compounds.
Function of basophils. (2)
- Similar role to eosinophils and mast cells
- Important for allergic response (release of histamine, causes inflammtion).
Function of mast cells. (2)
- Only found in tissues
- Its cytoplasm is full of granules containing histamine and active agents which are important for recruiting other cells to site of infection, increasing inflammation and triggering muscular contractions.
Function of dendritic cells.
- Programmed to detect and phagocytose pathogens.
- Display foreign antigen on surface to present to lymphocytes.
- Involved in T cell activation.
Difference between immature and mature dendritic cells.
- Immature/resting DC: sample environment for antigen, phagocytic, pattern recognition receptors.
- Mature DC: morphological changes, migrate to lymph node, present antigen to T cells.
Function of NK cells. (4)
- Secrete anti-viral cytokines. eg. interferon-gamma and tumour necrosis factor-alpha.
- Respond to changes in expression of self proteins.
- Activated NK cell release perforin and granzymes that together trigger the target cell to commit suicide.
- May also recognise and kill cells opsonised by antibodies (ADCC).
Function of complement. (4)
- Soluble proteins in blood that can interact with pathogens to mark them for killing.
- Activated sequentially in a cascade, which can be activated by 3 different pathways.
- All pathways converge at the activation of C3 protein to C3a (recruits phagocytes/inflammatory cells) and C3b (tags bacterium for destruction/phagocytosis).
- The 3 pathways are classical, lectin and alternative.
What can antibodies do?
- Opsonise bacteria, neutralise viruses, sensitise mast cells and activate complement.
What does a naive cell mean?
- Haven’t encountered a foreign antigen yet.
What is the difference between negative and positive selection of B cells?
- Negative mean alteration, elimination or inactivation of B-cell receptors that bind to components of the host body.
- Positive mean promotion of a fraction of immature B cells to become mature B cells in the secondary lymphoid tissues.
What is conformational epitope and linear epitope?
- Multiple different amino acids coming together in the shape of their 3-D structure (no continuous).
- Continuous amino acids in a linear fashion can be recognised.
- Denaturation results in the loss of conformational epitopes.
Difference between surface Ig and secreted Ig.
- Secreted Ig has hydrophobic tail removed so it doesn’t embed into cell surface.
What is Fc and what is Fab?
- Stalk of Y is the crystallisable fragment and is composed of only the constant region.
- Top of Y is two antigen-binding fragments composed of both a constant and a variable region.
What are the 5 classes/isotopes of immunoglobulin and what region of the antibody do they reside in? (3)
- IgM, IgD, IgG, IgA, IgE
- Determined by the heavy chain constant region gene segments.
- Effector function of antibody is largely derived from the Fc region.
Describe IgM. (4)
- Expressed as receptor on naive B cells and early during infection.
- Secreted as pentamer
- Linked by J chains
- Efficient at activating complement
Describe IgG. (4)
- Major immunoglobulin class in serum and secondary response.
- Binds receptors (FcRs) expressed by monocytes, macrophages and NK cells.
- Can activate complement
- Can cross placenta
Describe IgA. (3)
- Expressed on the cell surface as a monomer
- Secreted as dimer (held together by J chain that binds to the secretory component)
- Prominent in mucosal secretions (airways, gut, breast milk)
Describe IgD. (2)
- Expressed on naive B cells (along with IgM)
- Not really seen in secreted form
Describe IgE. (2)
- Important in responses to parasites.
- Can cause allergic reactions.
Where does thymic education occur and what selections are involved? (3)
- Occurs in thymus where TCR is first expressed.
- Positive selection: If TCR has no capacity to bind slef MHC molecules, the T cell will die.
- Negative selection: If TCR binds to host MHC/peptide complexes present in thymus too tightly, T cell will die.
Describe the structure of a TCR. (4)
- Heterodimer of the alpha and beta chain
- Membrane bound
- Multiple V gene segments
- One constant-alpha gene segment and one constant-beta gene segment
Function of T cell receptors.
- Can only bind short linear epitopes.
Which cells express MHC class 2?
- macrophages, B-cells and dendritic cells
What proteins are presented on MHC 1 and MHC 2?
- Present peptides from endogenous proteins.
- Present peptides from exogenous proteins.
How is peptide presented onto MHC class 1? (2)
- Peptides are created by proteolysis in the cytoplasm by proteasome.
- Peptide transported through TAP and loaded into MHC class 1 in the lumen of the ER.
What are the 3 signals required to activate naive T cell?
- Presentation of MHC and antigen to TCR.
- Costimulation through CD28:B7 (CD80/86) for T cell expansion.
- Cytokine receptor signalling for T cell differentiation.
How is dendritic cell activated and what results from it?
- Binding of pathogens, signalling by PRR (on DC) following ligation with molecular patterns (PAMPs) on pathogens.
- Increased surface expression of MHC 1 & 2, expression of co-stimulatory molecules (CD80, CD86), secretion of cytokines, Mature DCs lose capacity to capture antigen.
