Immunology Flashcards
Where are mast cells most commonly found?
The connective tissue (under the skin) and the epithelial mucosae (the respiratory and intestinal epithelia).
Which chemicals are secreted by mast cells when IgE binds to the cell surface?
Histamine and leukotrienes.
What are the effects of inflammatory mediators released by mast cells upon blood vessels and smooth muscle?
In connective tissue, vasodilation is caused, increasing blood flow near the surface of the skin and oedema. Around mucosae, smooth muscle constricts, causing constriction of the airways and intestinal walls.
What is urticaria?
A skin rash caused by an allergen. Stimulation of connective tissue mast cells causes vasodilation leading to the red colour of the rash, and oedema leading to its raised appearance.
What are the symptoms of a reaction to an inhaled allergen?
Stimulation of epithelia in the nose - leading to mucus secretion.
Contraction of smooth muscle of the bronchioles in the lungs, alongside inflammation and increased mucus secretion. This leads to difficulty breathing.
What are the symptoms of an allergen that is ingested?
Vomiting and diarrhoea due to constriction of smooth muscle lining the GI tract. If the allergen is absorbed and passes into the blood stream it may also cause skin symptoms.
What is anaphylaxis?
A SYSTEMIC response to an allergen causing immediate responses throughout the body.
List symptoms of anaphylaxis.
High RR and HR.
Nausea, abdominal cramps and/or diarrhoea.
Difficulty breathing.
Describe the emergency treatment given to someone undergoing an anaphylactic reaction.
First tackle hypotension –> then underlying inflammation
Lay them down with feet up to improve blood supply to head and torso. Inject adrenaline to constrict peripheral blood vessels. May need to control BP using IV.
Then administer antihistamines and anti-inflammatory corticosteroids.
If breathing problems persist oxygen may be required and bronchodilators given by inhaler.
What substances can cause anaphylaxis?
Ones which can pass freely throughout the body.
Penicillin (especially if previously given by IV), some other drugs (local anaesthetics and x-ray contrast agents), venom, peanuts.
Which 2 pattern recognition receptors (PRRs) does the innate immune system use?
PAMPs - pathogen-associated molecular patterns
DAMPs - damage-associated molecular patterns
Give 2 examples of PAMPs
Flagellin of bacteria, envelope glycoproteins of viruses
Give 2 examples of DAMPs
Extracellular ATP, heat shock proteins.
What are primary lymphoid organs?
Sites where lymphocytes are produced by lymphopoiesis (B and T lymphocytes)
What are secondary lymphoid organs and give 3 examples.
Sites where lymphocytes can interact with antigen and other lymphocytes.
Spleen; lymph nodes; mucosal associated lymphoid tissues (MALT).
Describe lymphocyte recirculation.
Naïve lymphocytes enter the blood from the primary lymphoid organs. The lymphocyte circulates through the peripheral lymphoid tissues. If it comes across its antigen being presented, it becomes activated. If not, it recirculates until death.
Describe the extravasation of naïve t-cells into lymph nodes from high endothelial venules (HEVs).
The t-lymphocytes roll along the wall of the HEV, adhering weakly by selectin. Integrin is a low-affinity binding form. When chemokine on epithelial cell surface binds to chemokine receptor on the lymphocyte, the integrin changes to a high-affinity binding form. Then lymphocyte then undergoes transendothelial migration. NEUTROPHILS also migrate into tissues by this mechanism.
Describe the structure of lymphocytes.
Small cells with agranular cytoplasm and large spherical nucleus.
What are cluster of differentiation (CD) markers?
Cell surface markers used to differentiate between cells of the haematopoietic system.
What are CD4+ cells?
Helper T-cell (regulatory function) - secrete cytokines.
What are CD8+ cells?
Cytotoxic T-cells which lyse infected cells.
What are antigen presenting cells (APCs) and give 3 examples.
Cells which can present processed antigens to T-lymphocytes to initiate an adaptive immune response.
Dendritic cells, B lymphocytes and activated macrophages
What do mast cells do?
Release granules (containing histamine and leukotriene) - pro-inflammatory.
What are the functions of monocytes/macrophages?
Phagocytosis, killing microbes, cytokine release, APCs.
What’s the function of eosinophils?
Defence against parasites.
What is opsonisation?
The coating of microbes with proteins (OPSONINS) to facilitate phagocytosis.
What are neutrophil extracellular traps (NETs)?
Activated neutrophils release granule proteins and chromatin to form extracellular fibres, trapping microbes. This enhances phagocytosis.
What’s the difference between monocytes and macrophages?
Monocytes circulate in the blood and become macrophages when they migrate into tissues.
How do macrophages function?
They express receptors for many different bacterial constituents. Binding stimulates the release of cytokines (alerting the immune system). They then engulf and destroy the bacterium.
How does vasodilation and increased vascular permeability (caused by mast cells) help the immune system?
Slows blood flow at the site of infection.
What are natural killer cells?
Large granulated lymphocytes. They lyse infected cells. They have receptors which bind to antibody-coated cells. Self recognition –> leave target alone. Missing self –> lyse target cells.
What are cytokines, their effects and characteristics?
They are small secreted proteins, used for cell to cell communication, generally acting locally. They have biological effects at low concentrations.