Immunology Flashcards
What are the functions of a macrophage
- Debridement/ removal of injured tissue and debris (phagocytsosis, collagenase, elastase)
- Chemotaxis and proliferation of fibroblasts and keratinocytes
- Angiogensis
- Deposition and remodelling of ECM
What cell orchestrates tissue repair
Macrophages
What host factors influence inflammation and repair (5)
Nutrition
- Protein, vitamin C
Metabolic status
- Healing is slower in diabetics
Steroids
- Anti-inflammatory and slow collagen synthesis
Infection
- Most important cause of delayed healing
Mechanical factors
- Excessive movement slows healing
Blood supply
- Impaired in diabetics and other disorders
Do dead cells stain more pink or purple
Stain deeper pink (E) due to increased eosinophils, and loss of RNA decreases the purple (H)
What are the major components of innate immunity
- Activation of alternative complement pathway
- Phagocytosis
- Acute phase proteins
- Natural killer cells (In intracellular)
- T and B cells not involved (with the exception of IGM antibodies)
- Inflammatory response exemplifies the innate response.
- Little specificity
- Same reaction each time
- No memory
Outline the role of macrophages in acute inflammation (extracellular i.e bacterial infection)
- Constantly surveying environment phagocystosing and looking for danger signals.
- To activate a macrophage you need 2 steps.
1. Phagocytosis
2. Danger material - Toll like receptors (inside macrophages detect danger materials).
= activation of inflammation
Once activate they make THREE critical cytokines.
- IL-8: Goes to the bone marrow and recruits NEUTROPHILS (chemokine)
- TNF alpha and IL-1, alter endothelial wall to allow neutrophils to stick to it and enter tissue (Margination and diapededesis)
- i.e they make the endothelial cells express receptors (activation) and the neutrophils also have the same receptors/ appropriate adhesion molecule
CD nomeculature
Polypeptide on surface of cells that induce the formation of antibodies.
May be exclusive to a cell type of broadly distributed.
- CD3 = T cell
- CD4 = Th cell
- CD8 = Tc cell
- CD19 or 20 = B cell
- CD11c = DC
- CD56 = NK cell
- CD14 = Monocyte
What is the complement cascade
Complement - a series of 9 major proteins which act in sequence to clear potentially pathogenic material from blood and tissues.
What is the function of the complement cascade
Central aim: to split C3, the most abundant
complement component, to generate the components that
– opsonise microorganisms (labels them)
– degranulate mast cells to release
chemotactic+inflammatory mediators
(e.g.histamine) (i.e chemotaxis)
– assemble the ‘membrane attack complex’ (MAC) which causes perforations (i.e destroy)
What are the 3 complement pathways
- Alternative pathway/bypass (LPS)
- Lectin pathway
- Classical pathway (antibody)
Describe how the alternate and lectin pathways activate complement
- Complement is an inert protein present everywhere.
- It gets activated by LPS and other moietes on bacteria.
- Enzymes chop up C3 and C5 into C3a, C3b, C5a, C5b.
C3a and C5Aa then release IL-8 (chemotactic) and result in the degranulation of mast cells (vasodilation). THIS IS NOT THE SAME AS ANAPHYLAXIS
C3b = Helps speed up phagocytosis (Opsonisation!)
C5B = Binds, to 6,7,8 + ring of C9 (MAC), which essentially punches a hole in bacteria (osmotic lysis).
Receptors that clear complexes containing C3
- CR1: on RBC, monocytes, granulocytes, B cells - provide
entry for mycobacteria, leishmania - CR2: on B cells - provide entry for EBV, and HIV
- CR3: on macrophges, NK cell and polymorphs -
provide entry for mycobacteria - CR4:
(lots of ways for viruses to target complement and invade a cell)
What type of bacteria is the complement pathway particularly important in treating
Gram negative
How do we protect host cells from the effects of complement?
Membrane-bound complement inhibitors on cells include:
DAF (decay accelerating factor) and MCP (membrane
cofactor protein) which break down C3 convertase
HRF (homologus restriction factor) C8 binding protein and CD59 which prevent the formation of MAC on host cells
What are the vascular reactions in acute inflammation
Vasodilation and an increase in vascular permeability
- NO, histamine, serotonin
- Vessels affected are arterioles, capillaries and
venules at site of infection. - Cells get pulled apart
Mediators in acute inflammation
Histamine
Serotonin
Prostaglandins
Leukotrines
PAF
ROS
NO
Cytokines
Neuropeptides
Complement
(C3a, C5a, C3b, C5b-9)
Kinin system
Coagualtion/fibrinolysis
What are acute phase proteins and what are their function
- Fibrinogen (helps wall off infection via fibrin)
- CRP-1 (Helps chop up complement)
- Haptoglobin (Reduces availability of iron to bacteria)
- Mannose binding protein, amyloid a, serum amyloid P, C’ proteins and coagulation proteins
What are natural killer cells
Essentially just granular lymphocytes
What stimulates the release of acute phase reactants
TNF goes to the liver
Which cytokine is responsible for fevers
IL-1
Outline the early response to viruses (i.e how they get into cell and what they do inside)
Viruses have to bind to a cell surface receptor (sometimes a complement receptor).
They then gain access into the cell then they can replicate and lyse cell.
Once inside they try to hide from cytotoxic T cells. They do this by down-regulating the expression of MHC1 (or killing activator). As ALL nucleated cells express MHC1.
What is a natural killer cell and how do they get activted.
Essentially the viral version of a macrophage.
Alternatively called large granular lymphocytes.
Their activity is inhibited when they see MHC1 on target cells.
- THEREFORE they recognise when cells infected with viruses have down-regulated MHC1 (to try and escape cytotoxic T cells).
- They have CD16 Fc receptors for igG
- I.e they can acquire an antibody and allow antigen specific recognition
- This is called anti-body dependent cell mediated cytotoxicity
Can you tell the difference between lymphocytes under the microscope.
No B cells and T cells look the same.
They have a very large nucleus compared to cytoplasm.
NK cells however have granulocytes so you can differentiate them on the blood smear.
Two ways that NK cells result in apoptosis.
- Upon activation, NK cells release cytotoxic granules containing perforin and granzymes to directly lyse tumor cell.
- Activated NK cells express FAS ligand which interacts with FAS on APC (extrinsic pathway)
(same mechanisms as Tc cells)
Where are lymphocytes made
All lymphocytes are made in the primary lymph tissue
- T cells: Thymus
- B cells: Bone marrow
Describe T cell development in the thymus
All T cells begin as double negative.
I.e they do not have CD3, CD4, or CD8.
They then begin to express T cell receptors. CD3 (alpha/beta OR delta, most are alpha or beta), CD4 and CD8. They have now gone from being double negative to double positive.
They then drop EITHER CD4 or CD8 to become T helper or cytotoxic T cell.
CD4 = helper CD8 = toxic
They then learn how to recognise MHC and learn to not respond to self peptide before being exported to the periphery.
How many T helper cells do you get for each cytotoxic developed
2
Which T cell recognises which MHC
CD8 = MHC1
CD4 = MHC2
What antibody do all B cells express
IgM
How do lymphocytes enter the lymph nodes and the spleen
Via the blood or via the AFFERENT lymph
Only enter spleen via the blood
Where are B cells and T cells located in the lymph node and spleen
They are separated out.
Lymph node
- T cells: Paracortex (centre)
- B cells: Outer cortex
Spleen
- T cells: Inner region of PALs (DC here)PA
- B cells: Marginal zone or outer region of PALS
What cell is responsible for activating T cells and how/where does this occur.
If the stimulus persists and we haven’t been able to clear the infection with the innate immune response.
Dendritic cells will start getting ready to interact with T cells.
Only happens in the lymph not in the periphery.
Dendritic cells are responsible for priming T cells.
How do we present antigens to cells
If APC is phagocytosing cells we get MHCII interacting with Thc (CD4) (naive)
If APC is cystolic derived we get MHC-1 and cytotoxic T cell CD8
What is an antigen
Any substance that can bind to an antibody and generate and immune response (i.e immunogen)
OR react with antibody/T cells but do not generate an immune response
e.g hapten which can only generate a response if it is couple to a carrier CNP
Are antigens big or small
Generally high molecular weight but can have low molecular weight carbohydrate antigens
What is an epitope
Small part of an antigen recognised by the antigen combining site of an antibody (paratope) or a T cell receptor.
Comprises 6 amino acids of linear protein or up to 21 amino acids of a globular protein
(conformation important -degradation = no
recognition)
Do TCR and B cells recognise the same epitope
Not necessarily
What is MHC/HLA
- It is the molecule that presents antigens to T cells (derived from inside or outside the cell)
- Conserved in evolution
- Essential for recognition of a foreign antigen
What chromosome is HLA coded on, how many regions are there, what are the products of each region
Short arm of chromosome 6
Class 1 region
- A, B, C, E
Class II
- Putative peptide transported
- DP, DQ, DR
Class 3
- HSP70
- C2 and C4
Is HLA polymorphic and explain the implication
Yes, very polymoprhic
This means it can express millions of different peptides
How is HLA Expressed, compare this to B cells and explain the implication
HLA is co-dominantly expressed.
This means that both copies you get from your parents are expressed (instead of one or the other), this means that you can present even more peptides.
(Unlike B cells when you can only express one antibody e.g IgG or igA)
Outline the structure of MHC
- Heterodimer (an alpha and a beta chain)
- On MHC1 - the alpha chain forms the peptide binding groove and has a b2 microglobulin which stabalises the alpha chain has 1 cytoplasmic tail
- On MHCII the alpha chain and the beta chain, has 2 cytoplasmic tails. MHCII is bigger than MHC1 therefore can hold a bigger peptide.
- MHC look similar to T cell receptor
- NOT biochemically similiar to B cell receptor
- To be stable they have to have a peptide in their binding site (most of the time this is just self peptide)
How is HLA passed on
In blocks, i.e the offspring of 2 parents can only give 4 different combinations
(linkage disequilibrium)
What is MHC restriction
A T cell recognizes antigen as a peptide bound by a particular allelic variant of an MHC molecule, and will not recognize the same peptide bound to other MHC molecules.
How do we activate Th cells
Requries 2 signals
Signal 1: Interaction between MHC and peptide complex
Signal 2: Co-stimulatory molecules.
CD80/86 (dendritic): CD28 (Tcell)
Activation of antigen presenting cell required to induce co-stimulatory molecules (danger signals)
Outline the structure and function of a T cell receptor
- Any naive T cell expresses a UNIQUE receptor for a specific antigen.
- All receptors on that T lymphocyte will be the same
I.e CAN ONLY REACT TO ONE ANTIGEN - NOT secreted (unlike B cell receptor/antibody)
How many gene segments are required to make a BCR and TCR
7
What segments are on the alpha chain of a TCR and what are on the beta chain
- V,J and C region (a chain)
- V,D, J and C (b chain)
Do TCR show generation diversity
Yes the different segments are spliced and transcribed etc