What the is advantage of direct microscopy?
It is quick, easy and cheap to perform with a light microscope
What are the main advantages of direct molecular tests?
Where are T cells within the lymph nodes?
What cytokines produced by the stroma of the lymph node attract B lymphocytes out of the blood?
What are the cells called in the dark zone of the germinal centre?
What cytokine pushes CD4+ cell towards a Th-1phenotype?
Which part of the lipopolysaccharide molecule is the toxic moiety?
The lipid tail; causes inflammatory response.
What bacteria causes Scarlet fever?
How does a T cell recognise an antigen in a MHC class II receptor on a B cell
Through the T Cell Receptor (TCR)
What cytokine released by T helper cells acts in an autocrine fashion to stimulater proliferation?
How do Type I exotoxins produce damage to the host?
They alter host cell signal transduction, from outside of the cell
Through what structure do lymphocytes in the blood enter the lymph nodes?
Through the high endothelial venules (HEVs)
What is the process called whereby self-antigen recognising B cells are destroyed?
What is the name of the cells found in the basal light zone of the germinal centre?
What are virulence factors?
A variable that denotes the capacity of a organism to cause infection
How many B cells are produced and leave the bone marrow per day?
2.5 billion cells
Roughly what percentage of lymphocytes enter the spleen and how long do they spend there?
45% remain in the spleen for about 5 hours.
What cell types are found within the primary follicle?
- B lymphocytes
- Follicular dendritic cells
What are the 3 main things competent dendritic cells provide?
- MHC and peptide
- Co-stimulatory surface molecules such as B7-1
- T-cell activating cytokines such as IL-12
What are the disadvantages of direct molecular tests?
- Easy to contaminate with nucleic acids from other organism
What mechanisms can be used by microbes to evade the human immune system?
- Shedding of antigen or changing the antigens during infection
- Resistance to phagocytosisInterference with antibodies or complement
- Resistance to complement-mediated lysis or macrophage killing
- Inaccessible to immune system
- Mimicry of host antigens
- Interfere with MHC molecules
- Bind to and inhibit cytokines
How can lipopolysaccharide (LPS) cause endotoxic shock?
- It binds to LPS-binding protein which is recognised by macrophages through the CD14 receptor
- This leads to an over-production of cytokines including PAF, TNF-α, IL-1, IL-6 and IL-8
- This leads to activation of the coagulation cascade, production of prostaglandins and leukotrines and also activates the complement cascade
How can microbes cause direct damage to the host?
- Harmful metabolites
- Degradative enzymes and toxins
- Growth in host cells
How are CD4 T cells activated?
Antigens on tissue dendritic cells.
What are the disadvantages of serological tests
- Must screen specific pathogens
- No sensitivity results.
What cell types is MHC class I found on?
All nucleated cells of the body
Briefly describe the process of monoclonal antibody production?
- Animal is injected with specific antigen, and after a length of time the animal is sacrificed and a B-cell suspension is produced from the spleen
- Myeloma cells are mixed with the B-cell suspension, and a detergent is added to help fusion of the B-cells and myeloma cells
- They are added to a special medium that only allows the hybridomas to proliferate and grow
- Each hybridoma is then screen for the desired antibody
- The selected hybridoma is then grown on a commercial scale to produce vast quantities of monoclonal antibodies
What happens in the dark zone of the germinal centre?
- Proliferation of centroblasts - clonal expansion
- Somatic hypermutation
How do Type III exotoxins gain entry into the host's cells?
- Injection by the pathogen using a Type III apparatus
- Receptor mediated endocytosis; A-B toxins.
Describe endotoxins produced by bacteria.
- They are released on bacterial death, as they are found in Gram -ve cell walls
- They are lipopolysaccharide complex and are relatively stable
- Weakly toxic
- Synthesised from the nucleoid
What is the difference between monoclonal and polyclonal antibody production?
- Monoclonal antibodies are produced by the division of a single B cell
- Polyclonal antibodies are produced by the division of multiple B cells each with a different antigen binding specificity
Describe briefly the process of polyclonal antibody production.
- Animal is injected with specific antigen to induce antibody production
- After a few days, blood is taken and antibodies purified from it
- The purified polyclonal antibodies can be used to detect the original antigen
What cytokine pushes the CD4+ cells towards the Th-2 phenotype?
Where in the lymph nodes do B cells aggregate?
What is the chemokine that follicular dendritic cells secrete to attact B cells to the primary follicle?
If an unbound antigen is captured by a B cell, what receptor is that antigen presented in?
MHC class II
What are the 4 main categories of exotoxin, based on their site or mechanism of action?
- Cell or tissue degrading enzymes
- Toxins that alter cell signalling pathways
What cytokine is released by Th-2 cells?
What happens in the apical light zone of a germinal centre?
B cells present their antigen to Th cells, if they recognise each other, the B cell differentiates into plasma or memory cells
What is affinity maturation?
- There is random mutations in the V-region genes, that code for the CDR
- This affects the ability of B cells to bind to the antigen
- The stronger the match, the more likely the cell is to survive
What are the disadvantages of culturing a pathogen?
- Long time to get results
- Certain pathogens hard/impossible to culture
- Certain pathogens to dangerous to culture
- Can't always differentiate pathogen or commensal
What is MHC restriction?
It where a T cell will only recognise 1 class of MHC
- CD4+ cells can only recognise MHC class II
- CD8+ cells can only recognise MHC class I
What toxins can Staphylococcus aureus produce and what diseases do they cause?
- It can produce toxic shock syndrome toxin, which causes toxic shock syndrome
- It can also produce exfoliative toxin which leads to scalded skin syndrome
What receptors must interact to fully activate the cells?
- MHC class II - TCR
- CD40 - CD154
- B7RP - ICOS
What cytokine is released by Th-1 cells to activate macrophages?
What are the 4 main techniques used in identification of pathogens?
- Serological tests
- Molecular tests
What are the 3 types of exotoxin (based on where they act on the cell)?
- Type I - Membrane acting
- Type II - Membrane damaging
- Type III - Internally acting
What toxin is produced by E. coli and what common disease can this cause?
It produces enterotoxin which causes diarrhoea
What are the symptoms of endotoxic shock?
- Acute respiratory distress syndrome
- Disseminated intravascular coagulation
- Multi-organ system failure through endothelial damage
What happens in the basal light zone of a germinal centre?
Centrocytes are selected by follicular dendritic cells = affinity maturation
Describe exotoxins produced by bacteria.
- They are actively produced by Gram -ve and +ve bacteria
- High Molecular weight polypeptides
- Relatively unstable
- Highly toxic
- Synthesised from plasmids
Where are Interdigitating dendritic cells found in the lymph node?
In the T cell region of the paracortex
What are the main disadvantages of direct microscopy?
- Can only use certain types of sample
- Requires personal with specialist training - electron microscope
- Electron microscope expensive to install, maintain and use
- No antibiotic sensitivities can be performed
What are the advantages of serological tests?
- Quick, easy and cheap to use
- Moderately sensitive
- Good specificity
- Detect pathogens that can't detect be cultured
- Can be automated
What are the 2 types of Type II exotoxins and how do they cause damage?
Pore forming; generate a channel leading to disruption of the membrane potential
Enzymatic enzymes; destroy the phospholipid integrity of the host cell membrane.
What surface immunoglobulins are found on the virgin B cells?
What is contained in the cytotoxic granules of CD8 effector cells?
What is another name for the disease scalded skin syndrome?
Toxic epidermal necrolysis
What are the other endotoxins apart from LPS?
- Bordetella pertussis tracheal cytotoxin (TCT)
- Streptococcus pneumoniae pneumolysin
- Various muramyl dipeptides
On what cell types are MHC class II found?
All activated antigen presenting cells.
How can microbes cause indirect damage to the host?
- Inflammation and the immune response
- Use of host nutrients such as Fe
What bacterium is responsible for whooping cough?
What do activated macrophage use in order to kill phagocytosed bacteria?
- O2 radicals
- Nitrous oxide
What are the advantages of culturing a pathogen?
- Relatively cheap to perform
- Viable organism grown so antimicrobial sensitivities can be performed
What is virulence?
The ability of of a micro-organism to cause disease.
What percentage of lymphocytes enter the lymph nodes via afferent lymphatic vessels?
What are the disadvantages of polyclonal antibodies?
- The mixture is not very specific
- Antibodies are short-lived so must re-bleed animal every time you want them
What toxin is produced by Corynebacterium diphtheiae and what disease does it cause?