Immunology 1 Flashcards
List the 4 main functions of macrophages
1) Antigen presenting cells (APC) ingest and kill microbes -> PAMPS
2) highly phagocytic
3) clearance of RBC, WBC, apoptotic cells - DAMPS - damaged cells
4) Produce cytokines – signalling and amplification of immune response and colony stimulating factors – haematopoiesis
What are the 3 main killing mechanisms of neutrophils and examples of granules
3 killing mechanisms 1. phagocytosis 2. degranulation 3. NETs - neutrophil extracellular traps Primary (azurophilic) granules: - Larger, denser - Contain peroxidase, lysozyme, hydrolytic enzymes Secondary (specific) granules: - Smaller - Collagenase, lactoferrin, phospholipase
What are the 3 main areas mast cells are found and roles there
1) Gastrointestinal tract - important for parasites and worms
2) Airways - decreased diameter - prevent more pathogens from entering and increased mucus secretion - entrap the microbes
3) Blood vessels - as mast cells degranulate increase permeability of the blood - if get systemic infection can cause anaphylactic shock as too much leakage through blood vessels throughout body causing a decrease in blood volume and pressure
List 2 mediators from mast cells, basophils and eosinophils and their functions
Mast cells and basophils
1) histamine -> increase vascular permeability, stimulate smooth muscle contraction
2) Prostaglandin D2 -> Vasodilation, bronchoconstriction, neutrophil chemotaxis
Eosinophils
1) peroxidase -> degrades helminthic and protoxoan cell walls
2) leukotrienes C4 -> prolonged bronchoconstriction, mucus secretion, increased vascular permeability
What are Yδ T cells where found and function
mainly present in high levels in ruminants and neonatal animals
Only have a limited amount of molecules it can recognise unlike other T cells
List the 4 main anatomical and physiological barriers
1) Epithelial Barriers
- Skin and mucosal membranes, Tight junctions, keratin, apid turnover rates
2) Secretions
- Lysozymes, Antimicrobial peptides, oxidative radicals, Intraepithelial lymphocytes
3) Effector cells
- Macrophages, Neutrophils Mast cells, Eosinophils, Natural killer (NK) cells
4) Effector proteins
- Complement proteins, Acute phase protein eg Mannose binding lectin & C-reactive proteins
List the 6 features of the gut that acts as a barrier to infection
1) intestinal epithelial cells - physical
2) goblet cells -> produce mucus -> trapping
3) paneth cells -produce antimicrobial peptides and alpha defensins when given signals - cytokines -> insert themselves into membranes and form pores in the membranes that destroy the pathogen
4) M cells - sample intestinal lumen and stimulate cells within the peyer’s patches below if foreign material detected
5) Peyer’s patches
- lymphoid aggregates
6) Lamina propria
- Lymphocytes, B cells, dendritic cells, macrophages, plasma cells IgA
Describe the two main molecules that are involved with the activation of the innate immune system and give 2 examples
- Pattern-recognition receptors (PRR) expressed by cells of innate immune system and detect microbes
- Limited repertoire (recognize 103 molecular patterns) - Pathogen-associated molecular patterns PAMP = unique microbial molecules (PAMP) shared by groups of related microbes not found associated with mammalian cells.
1) Flagella protein
2) peptidoglycan from the cell wall
What are the 4 main types of PPR and main types within (example if needed)
1) Cell surface
1. Mannose receptor
2. scavenger receptor
3. N-formyl Met receptor
4. opsinon receptor
2) Cell surface signalling
- Toll-like receptors - TLR-4 (LPS)
3) endosomal
- other Toll-like receptors - TLR-3 (double-stranded viral RNA)
4) Cytosolic
- NOD like receptors
Cell surface PRR what are the 4 types of receptors and their function
1) Mannose receptor - bind lectins and mannose rich glycans
2) scavenger receptor - bind to bacterial cell wall components, LPS
3) N-formyl Met receptor - promotes motility and chemotaxis of phagocytes
4) Opsonin receptors - allows others to bind acute phase proteins, complement pathway, immune complexes
What are the functions of the PRR cell surface signallying and endosomal
1) Cell surface signalling
- TLR-4 recognise LPS
- Most use a intracellular signalling pathway within the cell that involves gene transcription of inflammatory cytokines and chemokines and antiviral chemicals such as interferons
2) Endosomal
- TLR-3 binds double-stranded viral RNA
- Activates same pathway as TOL-like receptors on the cell membrane
Cytosolic PRR what type of receptors where found and function
NOD-like receptors
Two main families of PRR recognize PAMps within cytosol.
Family of proteins involved in both PAMP (and DAMP) recognition and in cell signalling.
Include
1. NOD-like receptors (NLR) family of over 20 members) recognize peptidoglycan component of bacterial cell walls
- Regulate pro-inflammatory pathways via NFkB signalling via transcription
2. RIG - like receptors (RLR) family of 3 RNA helicases that detect viral RNA within cytosol.
- bind viral RNA (SS and DS)
- Activate NFkB signaling but also release interferons via transcription
What are DAMPs
- Associated with cellular and tissue injury and the result of release of cytoplasmic or nuclear molecules.
- DAMPs recognised by receptors against mitochondrial DNA, heat shock proteins ,adenosine metabolites, DNA interacting protein (HMGB1) .
What are the 3 functions of natural killer cells
1) Killing of injured cells - DAMPS
2) Killing of infected cells - altered MCH1 or altered antibody (binding to Fc receptor)
3) Killing of phagocytosed microbes
What are the 2 ways NK cells ill microbes
1) Via Fc receptor on the NK cell (Fcƴ RIII) - Antibody dependent cellular cytotoxicity (ADCC)
- Antibody is altered when binds to antigens on the surface of infected cells allowing NK cells to bind via their Fc receptor
2) Inhibitory and activating receptors
What is the mechanism for NK cells that allows some cells to be killed and others not
1) Inhibition
The cells have activating ligand that binds to the activating receptor on the NK cell
Normal cells have MHC class 1 receptors that bind to the inhibitor receptor on the NK cell which prevents NK cell from destroying healthy host cells
2) Activating
- Infected cells still have the activating ligand that bind to the activating receptor on the NK cell however the MCH class 1 receptor has been modified or downregulated due to viral or bacterial infection therefore inhibition doesn’t occur
- This leads to the activation of the NK cell and therefore lysis of the target cell
Structure of antibodies, what is the variable region, what gives functional change and what occurs
Basic antibody structure is composed of 2 heavy chains and 2 light chains
- The combination of a light chain with a heavy chain determine the antigen binding site -> variable region
- Once bound structure changes in the tail of the antibody so it can bind to Fc receptors, complements etc. ACTIVATED
Tail is giving the functional difference
what are the two main functions of antibodies
1) Neuralisation - prevent virus , bacteria and toxins from binding to key molecules on cell surfaces or within the body by blocking the binding region
2) Opsonisation - focus immune cells and complement to pathogens leading to phagocytosis or lysis of the pathogen depending on the immune cell it binds to.
List 5 innate immune cells that have Fc receptors and what occurs with opsonisation with Abs
1) Neutrophil - degranulation
2) Eosinophils - mainly IgE that binds to mast cell then binds eosinophils and causes degranulation
3) NK cells - leads to apoptosis of the cell via ADCC - Antibody-dependent cellular cytotoxicity
4) Macrophage - phagocytosis
5) Complement - activation causing
1. Lysis of microbes
2. Phagocytosis via opsonisation with complement fragments with C3b production
3. Inflammation
What are the 5 antibody isotypes and their general functions and what is the same about them
HAVE SAME ANTIGEN SPECIFICITY
Heavy chain determine isotype
1) IgM - pentamer -first response, antibody secretion, opsonisation
2) IgA - dimer - gut, resist pepsin cleavage, neutralisation to prevent movement through mucus membranes
3) IgE - parasites, allergic response (mast cells and eosinophils)
4) IgG - secondary response, opsonisation, neutralisation, can go across placenta
5) IgD - B cell receptor
What is different in terms of placental transfer in horses, ruminants and pigs, dogs and cats, primate and rodents and why
1) Horses, ruminants & pigs - epitheliochorial placenta - there are 6 barriers
- No transfer of Ab via placenta so colostrum extremely important
2) Dogs & cats - endotheliochorial placenta
- Only -5-10% IgG transferred via placenta
3) Primates, rodents - haemochorial placenta
- IgG transferred
What are the 6 barriers in epitheliochorial placenta
- Endothelial cells, connective tissue, epithelial - baby
- Epithelial cells, connective tissue, endothelial - mother
In what species and why are immunoglobulins in colostrum important, what type and timing that it occurs
Horses, ruminants & pigs - epitheliochorial placenta so no transfer during pregnancy
- when born no calf antibodies so need maternal from colostrum until can make their own
- IgM, IgG and IgA - neonates suckle (calf 2L colostrum)
- Absorption maximal in first 24h after birth due to epithelial cells not having tight junctions at that point
- Fc receptor on intestinal epithelial cells allow Ab to be transferred
Passive immunisation what does it result in and examples
Short-term as injecting the antibodies straight into patients so not creating own antibodies
EG - Snake-bite anti-venoms have concentrated Abs purified from serum of vaccinated horses
List 5 features of a secondary immune response compared to a first
- A much faster reaction time
- A higher antibody response (typically 2-3 order of magnitude)
- A qualitatively different antibody response (i.e. different isotypes, generally more IgG)
- require T cell help while primary response can occur independently of T cells
- A higher affinity of the antibodies to the antigen
Define epitope and paratope
- Area on the antigen that is bound is called the epitope and the area on the antibody that binds to the antigen (combination of the variable region of the heavy and light chain) is the paratope
○ Paratope-epitope interaction through complementary 3 dimensional structure with specific biochemical proper1es (charge, hydrophobicity, conformation, hydrogen bonds) - amino acid sequence gives the specificity
What is the structure of the MHC class I and II molecules
- Self-molecule: Major Histocompatibility Complex (MHC)
○ beta pleated sheet with 2 alpha helixes on either side makes up the binding site for the peptide
1) Class I MHC - made of 3 alpha domains and 1 beta domain - the alpha 1 and 2 domains hold the peptide
○ Different for individuals
2) Class II MHC - Foreign antigen is small peptide derived from antigen (8-12 AA) and sits within the MHC complex
NK T cells what type of cell, what bind to and structure
NK T cell - different type of T cell
- Not variable between individuals
- Binds glycolipid on the pathogen - type of antigen
NKT TCR - NKT cell receptor binds to the glycolipid
T cell epitopes where found
- Could be exposed but does not have to be (can be within the organism)
- Peptides are selected from anywhere within the protein sequence
- Need to be able to be degraded to peptides of the right size
- Need to be associated with MHC
What are the 2 types of epitopes and what is important
1) Class I restricted T cell epitopes
2) Class II restricted T cell epitopes
• How the antigen is presented to the immune system is important because it determines the type of T cell that gets activated
What is important with activating B cells in vaccines
Respond to antigens outside the cell
- B cells recognise the 3D structure so needs to be perfect protein folding - Recognises 3 areas on the heavy and 3 on the light
- Can recognise amino acids not consecutive
○ Denaturing can change the folding so need to keep cool
○ Any 3D structure will be recognised including proteins with carbohydrates - glycosylation
Recombinant proteins produced in bacteria do not have carbohydrates
Native viral antigens are produced by mammalian cells, which can glycosylate proteins
What is important with activating T cells in vaccines
Repsond to antigen within cells
- T cells recognise the chopped up antigen so doesn’t need perfect folding just small epitopes
○ Don’t really care about glycosylation just need to cut to the right size - amino acids need to be consecutive
- Carbohydrates can affect how antigens are processed and which peptides are produced
Carbohydrates can interfere with antigen processing enzymes
What does CD4 and CD8 bind to
MCH molecules bind to TCR receptor on the T cells
- CD4 binds constant part of MHC II
– CD8 binds constant part of MHC I
Interaction with these molecules stablises the interaction between TCR and MCH molecules
What is the function of lymphocyte development and what are the steps
Lymphocyte development is designed to generate functional lymphocytes with useful antigen receptors that are not self-reactive
1) Takes a stem cell 2-3 weeks to development within thymus, cytokines leads to division and development of T cells
2) Selection then takes place to choose T cells with TCR appropriate for antigens, needs to be able to bind properly and not bind to self - apoptosis
What are the 2 types of T cell receptors their structure and the types of T cells
1) αβ TCR
- Two polypeptide chains α and β
- Constant and a variable regions.
- Single Ag binding combining site - Ag peptides bound to MHC
- CD4 TH cells bind MHCII
- CD8 TC cells bind MHCI
- Ag binding results in signal transduction
2. ƴδ TCR (5% T cells )
- Recognize antigens without involvement of MHC
- lipid antigens, heat shock proteins
○ Limited repertoire
What are the 3 steps that create the diversity within TCRs
1) Combinatorial diversity
- Genes for TCRs are present in pieces that can be combined in many different ways in different lymphocytes
2) Junctional diversity (second event that occurs after the combinational)
- diversity is further increased by adding or deleting nucleotides at the junctions
3) Third level of diversity
Two strands of the TCR receptor - need to make alpha and beta chain separately then join together to create different binding sites
What are the 5 steps in organsiation of TCR genes to form diversity of TCRs
- DNA rearrangement during TCR-α chain formation in the thymus
- Recombination activating gene (RAG) protein enzymatic complex - COMBINATIONAL DIVERSITY
- Loops out genetic material to be cut - DNA- Dependent Protein Kinases - Excises intervening DNA and forms DNA hairpin loop
- Terminal Deoxynucletidyl transferase (TdT) - randomly add a codons (nucleotides) to join Variable, Joining and Diversity regions to add further diversity in the receptor - JUNCTIONAL DIVERSITY
5) add the alpha and beta chains together to create the receptor - THIRD LEVEL
List the 6 steps in the development of the T cell
- Stem cells in bone marrow enter the outer cortical regions
- Pro-T cell in the thymus is a double negative no CD4 or CD8
- Proliferation occurs via IL-7 which is produced by the thymic stromal cells
- Recombination of the β and α genes leads to expression of TCR and CD4 and CD8 receptors
- The T cell is now a double positive with CD4 and CD8 - if doesn’t form the TCR receptor apoptosis occurs
6) Positive and negative selection of the T cells then occurs
Describe the steps of positive and negative selection for T cells within the thymus
- Thymic epithelial cells (reticular cells) present in the cortex display MCH molecules with different peptides
- TCR tries to bind and if can’t - signal for apoptosis - LACK OF POSITIVE SELECTION
○ If get weak interaction - TCR can progress - POSITIVE SELECTION
§ If it binds to MCH1 then becomes CD8 - CD4 downregulated
§ If it binds to MCH2 then becomes CD4 - CD8 downregulated - Dendritic cells or macrophages present antigens if TCR binds with high avidity then those cells again undergo apoptosis or if weakly or strongly bind to self-antigens - NEGATIVE SELECTION
How are self antigens presented in the thymus when not all are expressed there
- Autoimmune regulatory gene turned on in the thymus - allow cells to produce antigens that are self and only found in other tissues in the periphery
What occurs with the thymus and age and what implications may this have
size diminishes with Age
- Role sex steroid hormones causes decrease in size as when these levels increase probably already interacted many pathogens and building a repertoire
○ Therefore available repertoire is diminished
- This has implications following chemotherapy where lymphocytes are removed and need to be replaced