Case 7 SBA Flashcards
Define immunity
The ability of an organism to resist infection. Can be natural, artificial, active, or passive
Define immune response
The reaction of the cells and molecules of the immune system to the presence of a substance not recognised as self
Define immune system
The cells, molecules, and organs that provide us with specific (adaptive) and non-specific (innate) protection against foreign bodies
What are the four functions of the immune system?
Recognition, reaction, regulation, and retention
Describe active immunity
Requires the engagement of the innate adaptive immune response.
Activation of B cells that differentiate into plasma cells to produce antibodies
Has immunological memory so provides long term protection.
Describe passive immunity
No immunological memory.
Antibodies are transferred rather than actively generated.
Provides short term protection.
Example of natural passive immunity
Mother passing on antibodies to baby via placenta or breast milk
Example of artificial passive immunity
Giving antibodies from an immune individual directly to a non-immune individual
Define immunogen
Any molecule that can induce an immune response
Define antigen
Any foreign molecule that generates antibodies
Define epitope
The specific part of the antigen that binds to the antibody or T cell receptor
Describe the mechanism of B cells
Antigen presented to helper T cells on MHCII which triggers B cells to differentiate into plasma cells that can secrete antibodies
What are the functions of the antibodies secreted by plasma cells?
Opsonisation: neutralisation, agglutination, chemoattraction, natural killer cell activation, and classical complement cascade activation.
Describe how precursory T cells mature
They migrate to the thymus and become thymocytes. The thymocytes are trained to discriminate between self and non-self using MHCI complexes. Thymocytes then become either CD4 or CD8 T cells.
Describe CD4 T cells
Regulatory T cells, helper T cells, and memory cells. Recognise foreign antigens on MHCII complexes
Describe CD8 T cells
Cytotoxic T cells and memory cells. Recognise self antigens on MHCI complexes
Describe T cells
Antigen specific but can’t secrete their own antibodies. Can only recognise processed antigens presented on MHC complexes.
Describe helper T cells
Make cytokines, help maturation of B cells, and help activate cytotoxic T cells and macrophages.
Describe regulatory T cells
Actively supress activation of the immune system
Describe memory T cells
T lymphocytes that have previously encountered and responded to a specific antigen. Long lived and can expand to large numbers upon re-exposure to the same antigen
Describe the action of cytotoxic T cells
MHCI complex binds to antigens. If self, CD8 cytotoxic cells recognise and leave alone. If viral proteins are there instead, it is recognised as not self and a response is triggered - apoptosis is mediated by perforin and granzymes.
What are the lymphoid lineage cells?
B cells, plasma cells, memory B cells, T cells, and natural killer cells
What are the adaptive lymphocytes?
B and T cells
Are natural killer cells part of the innate or adaptive response?
Innate
What are the polymorphonuclear leukocytes/granulocytes and where to they come from?
Neutrophil, eosinophil, basophil, and mast cells. Come from the myeloid lineage.
What type of response do the granulocytes give?
Innate
Describe the function of basophils
Non-phagocytic, instead undergo degranulation – release molecules from the granulocytes to combat pathogen. Found in the blood. Stain blue/purple. Have two lobes in the nucleus.
Describe dendritic cells
Immature dendritic cells are mainly phagocytic, they constantly sample lymph to check for new pathogens. Mature when they encounter a new pathogen then does antigen presenting. Takes phagocytosed antigen to adaptive immune cells and stimulates their response (foreign pathogen on MHCII complex).
Describe the function of eosinophils
Are phagocytic, deal primarily with parasites. Very abundant in allergic and hypersensitivity diseases. Found in the blood. Stain pink/orange with a c-shaped nucleus.
Describe the function of mast cells
Sentinel cell found living in tissues. Non-phagocytic, instead release granules containing histamine and active agents. Major role in allergic response.
Describe monocytes
Differentiate into macrophages and dendritic cells. Only found in the blood. Agranulocyte/professional antigen presenting cell. Phagocytic and cytokine release. Large nucleus because of need to differentiate. Antigen presentation from blood.
Describe macrophages
Phagocytic (first response) and cytokine release. Antigen presentation. Found in lymph and tissue. Can either be fixed or roaming. Have pattern recognition receptors (PRR) on surface that recognise general pathogen cell surfaces that are either phagocytic or signalling
Describe the mechanism of macrophage phagocytosis
PRR looks for pathogen associated molecular patterns (PAMP). PAMP binds with PRR and induces cytoskeletal rearrangement to engulf the pathogen –> internalised phagosome binds with lysosome to form phagolysosome which releases reactive oxygen species to destroy it
Describe macrophage signalling
If pathogen level too high, signalling PRR activated which releases cytokines – PAMP binds to toll-like receptors which induces signalling cascade and activates transcription factors NFκB and IRF3/7 which make cytokines and cause inflammation
Describe natural killer cells
Free roaming cells found in all compartments. Check MHCI levels and kill abnormal cells – MHCI is downregulated in infection so lower levels detected by NK receptors trigger a response
Describe the natural killer cell antibody dependent cell cytotoxicity mechanism
NK cells are activated to degranulate when they bind to antibodies bound to the surface of targeted cells –> crosslinking of CD16 triggers the release of perforins and other proteins and target cell killing occurs through a process of apoptosis.
Describe neutrophils
Main function is phagocytosis but also activate bactericidal mechanism. Make up pus. Undergoes oxidative burst that destroys the cell as well as the pathogen. Found in blood. Stain purple and have a nucleus with three lobes.
What are the three major differences between B and T cells?
B cells directly recognise native antigens whereas T cells only recognise processed antigens (partly degraded and displayed as peptides on the surface of antigen presenting cells).
B cells differentiate to plasma cells to secrete antibodies whereas differentiated T cells do not produce antibodies.
B cells produce relative low amounts of cytokines and require specific differentiation and activation conditions whereas activated T cells produce large amounts of cytokines.
Describe the role of primary lymphoid organs in the immune system
Bone marrow created the cells and thymus trains T cells to differentiate between self and not self.
Describe the role of secondary lymphoid organs in the immune system
Spleen and lymph nodes filtrate harmful substances out of blood and lymph fluid, respectively. Immune response occurs within the secondary lymphoid organs.
Describe the origin of cells involved in the immune system
Bone marrow is the origin for all white cell types. Haematopoietic stem cells differentiate into common lymphoid progenitor cells and common myeloid progenitor cells that then further break down into specific cell types.
Describe the function of the innate immune system
The first line of defence against foreign invaders. It can distinguish between invaders and the self but not between different types of invader. Recruits the adaptive immune system by releasing cytokines.
Describe the response of the innate immune system
The same, non-specific response to every invader. Gives a fever response within minutes or hours.
What are the four components of the innate immune system?
Physical barriers, sentinel cellular barriers, complement cascade, and cellular induced innate responses.
Describe chemokines and give an example
A type of cytokine that stimulates migration and activation of cells, the ‘air traffic controllers’ of the cytokine world. Example CXCL-8 which is responsible for the recruitment of leukocytes to the site of infection.
Describe cytokines
Small proteins that alter the behaviour of other cells, particularly immune cells
Examples of cytokines
IL-1β, TNF-α, IL-6, and IL-12
TNF-α action
Lymphocyte activation, increases vascular permeability, activates natural killer cells, eases access of effector cells, causes fever
PRIME MEDIATOR IN SEPSIS
IL-1β action
Lymphocyte activation, improves access of effector cells at site of infection, causes fever
IL-6 action
Lymphocyte activation, causes fever
IL-12 action
Activates natural killer cells
Describe 1st generation antihistamines
H1 receptor blockers. Tend to be drowsy from anticholinergic effects, can cross the blood brain barrier. Examples are chlorphenamine, diphenhydramine, and doxylamine.
Describe 2nd generation antihistamines
H1 receptor blockers. Less drowsy as can’t cross the blood brain barrier. Examples are cetirizine/Zyrtec and loratadine/Claritin.
What are the mechanisms of antihistamines?
Neutral receptor antagonists or inverse agonists (induce the opposite effect to the endogenous agonist)
What are the uses of antihistamines?
Treating allergy, insomnia, motion sickness, and anxiety
Describe some pharmacokinetic characteristics of antihistamines
Oral route, 1-2 hours until peak effect, last for 3-6 hours or 8-12 if long-acting, wide distribution, metabolised by liver, excreted in urine
Major side effects of antihistamines
CNS: drowsiness, dizziness, tinnitus, fatigue
Peripheral antimuscarinic effects: dry mouth, blurred vision, constipation, urine retention
GI disturbances and allergic dermatitis can also occur
Describe muscarinic antagonists
Act as bronchodilators as inhibit ACh from reaching receptors. Mainly used in COPD. Reduce mucus secretion and may increase mucociliary clearance
SAMA
Ipratroprium bromide. Bronchodilation onset relatively slow and usually maximal 30-60 minutes after inhalation. May persist for 6-8 hours. Take 3 or 4 times daily
LAMA
Tiotropium bromide, glycopyrronium bromide, umeclidinium bromide, aclidinium bromide. Take all once daily except for aclidinium which is twice daily.
Side effects of antimuscarinic drugs
Dry mouth, GI motility problems, tachycardia, nausea
Side effects of inhaled corticosteroids
Oropharyngeal candidiasis may occur; adrenal suppression and reduced bone mineral density when taken long-term.
Side effects of oral corticosteroids
Suppression of immune response to infection, Cushing’s, osteoporosis, hyperglycaemia, muscle wasting, and growth inhibition - all from long-term use.
Describe the mechanism of action of corticosteroids
Interact with glucocorticoid receptors –> moves to nucleus –> inhibits NFκB –> inhibits histone acetyltransferase and recruits histone deacetylase 2 –> HDAC2 deacetylates and modulates gene transcription in target tissues
Describe the action of beclomethasone and budesonide
Takes weeks for full effect. Reduces inflammation: reduce activation of eosinophils –> reduce production of IgE –> reduces production of leukotrienes and platelet activating factor –> inhibits induction of cyclo-oxygenase pathway –> fewer inflammatory cytokines.
May also upregulate β2 receptor expression
Mechanism of action of β2 adrenoreceptor agonists
Cause relaxation of airway smooth muscle by increasing cyclic AMP through Gs.
Describe short acting β2 agonists
Examples are salbutamol and terbutaline. Use as needed for acute episodes. Take via inhalation and gives relief within 5-10 minutes. Maximal effect reached within 30 minutes and has a duration of 3-5 hours.
Describe longer-acting β2 agonists
Examples are salmeterol and formoterol. Given regularly twice daily. Slow onset so not appropriate for an acute episode. Roughly 12 hour duration - lipophilic structures aid duration. Used alongside corticosteroids