IMMUNOLOGY - Basic (B-cells/T-cells, Immunoglobulins, MHC) Flashcards
Which immunoglobulin passes through the placenta to assist foetal immunity?
IgG
What is the main immunoglobulin in human tears?
IgA
What receptors do macrophages have? (3)
- pattern recognition receptors which recognise microbial components
- surface receptors that recognise Fc portion of immunoglobulin and complement components. Binding of these receptors to their ligands enhances phagocytosis of antigen (opsonisation)
- MHC class II molecules on surface when activated - present antigen to helper T-cells. Secrete IL-12 which directs T-cell differentiation to Th1 subset.
What pro-inflammatory cytokines do macrophages produce?
Bacterial:
IL-1,
IL-6,
IL-8,
TNF-alpha
Viral:
IL-12 (NK cells),
IL-18
Tissue repair: IL-10, TGF-B
Which complements are involved in the terminal pathway (membrane attack complex) and its deficiency predisposes to Neisserial infections?
C5-C9 (C3 is also associated)
IL-2 is produced by what cells?
CD4+ cell
HLA Class I Antigens vs
HLA Class II Antigens
Class I : all nucleated cells, allows CD8+ cytotoxic T cells to recognise and eliminate virus infected cells
Class II:
Professional APCs: macrophages, dendritic cells, B cells,
Non professional APCs: endothelial cells, fibroblasts, epithelial cells
allows initiation of immune response by interaction with T-helper CD4+ cells
difference in structure between class 1 and class II HLA
HLA-1: 3 alpha subunits, 1 B2 subunit
HLA-2: 2 alpha, 2 beta (1 alpha chain, 1 beta chain)
What cytokines do TH1 produce? What is their role
What cytokines do TH2 produce? What is their role
Both TH1 and TH2 are types of CD4+ cells
TH1 - cell-mediated (intracellular)
TH2 - humoral (extracellular)
1. TH1 : IFN-gamma, IL2 –> B cells, NK cell and macrophage activation to attack intracellular pathogens.
- TH2: IL3, IL4, IL5, IL6, IL-13 –> mast cell and eosinophil activation and stimulate antibody production by B cells to attact extracellular parasites
What are the main functions of interferon? (3)
- activation of NK cells and macrophages
- directive antiproliferative action on tumour and virus infected cells
- increased expression of Class 1 HLA on infected/tumour cells
What cells produce interferon?
T lymphocytes & macrophages
Which immunoglobulin is the first antibody to appear in infection?
IgM
What pathway does IgA activate?
Activates the alternative complement pathway (unlike other antibodies that activate the classical pathway)
What are the main types of eicosanoids? (3)
- Prostaglandins
- Leukotrienes
- Thromboxanes
What is the role of thromboxanes? (3)
vs
What is the role of leukotrienes? (3)
thromboxanes block, leukotrienes leak**
thromboxanes:
vasoconstriction, platelet aggregation and bronchoconstriction
leukotrienes
Bronchoconstriction, vasocontriction and increased vascular permeability
What is the arachidonic acid pathway?
See diagram.
What is the effect of prostaglandin I2?
causes vasodilation and reduced platelet adhesion
What are the effects of prostaglandin E2? (5)
- vasodilation
- bronchodilation
- Release of pituitary hormones, adrenal cortex steroids and insulin from pancreas
- Macrophage activation
- Uterine contraction
What are antigens? Definition
molecules (sugars, proteins or glycoproteins) that are immunogenic (cause immune cell proliferation) and reactive (cause production of antibodies)
What are the main secretion chemicals from mast cells? (3)
What is their main function?
histamines, leukotrienes and prostaglandins
- They work on plasma endothelial cells to cause p-selectin protein translocation to the cell surface –> monocyte/neutrophil margination/activation into interstitial space.
- endothelial cell contraction which creates spaces between endothelial cells which allows plasma leakage through the pores into interstitial place to cause swelling/oedema (INCREASED VASCULAR PERMEABILITY)
- Nociceptor activation to cause pain (usually by bradykinins)
- smooth muscle relaxation –> vasodilation (localised hyperaemia)
What is the function of phospholipase A2?
breaks down phospholipids into arachidonic acid
What do macrophages secrete?
- IL-1 and TNF-alpha –> activates plasma endothelial cells cause selectins to translocate to endothelial cell surface to cause monocyte and neutrophil activation.
- IL-8 binds to receptor on endothelial surface cell membrane –> ICAM/VCAM proteins on cell surface membrane –> monocyte/neutrophil activation
What are the effects of IL-1 and TNF-alpha? (4)
- activates plasma endothelial cells cause selectins to translocate to endothelial cell surface to cause monocyte and neutrophil activation.
- activates hypothalamus to secrete PGE2 which initiates fever –> denaturation of pathogen proteins and increase metabolism.
- acts on liver to produce acute phase reactant proteins (CRP - also activated by IL-6)
- acts on bone marrow to increase leukocytosis.
What is the main difference between macrophage and neutrophil in terms of breakdown of pathogen process?
macrophage is APC cell so exposes antigens with MHC2 to cell surface
neutrophils breaks down and exocytosis the antigen. They also release NETS (chromatin) which attach to foreign microbes which are broken down by cathepsin G.
Where are complement proteins synthesised?
In the liver
What is the lysis mechanism of classical complement pathway?
antibodies (IgG) attach to antigens of PATHOGEN, exposing Fc portion to complement proteins
C1 attaches to Fc portion –> forms complement cascade complex in form of C1 + C4 + C2 +C3a/C3b + C5a/5b + C6 + C7 _ C8 + C9.
C3a/C5a - breaks off and is chemotaxic agent
for more WBCs to enhance inflammatory response
C5b/C6/C7/C8/C9 breaks off complement complex, forms a membrane attack complex (MAC) on cell surface of pathogen, creating a channel to allow water and Na+ influx into the pathogen, which eventually causes lysis of pathogen.
What is the mechanism of opsonisation part of the classical complement pathway?
C3b of complement after chemotaxis by C3a recruits macrophages/neutrophils (more often macrophages) has C3b receptor of macrophages to encourage phagocytosis of whole pathogen and complement protein complex.
OPSONISATION –> enhancement of phagocytosis
What are the 3 main mechanisms of complement pathway?
- Membrane attack complex
- Opsonisation
- C3a + c5a (chemotaxis)
What is the alternative complement pathway?
direct access of complement C3b to directly attach to antigen on pathogen (without antibody).
C3b releases c3a to enhance macrophage recruitment
C3b then attaches to C5b –> C6 + C7 + C8 + C9 which then breaks off to form membrane attack complex on the pathogen surface which encourages H2o and Na+ influx which causes lysis.
What is the mechanism of the lectin pathway?
mannose-binding lectin acts on the antigen on pathogen and recruits C4.
C4 –> C2 –> C3b –> C5b –> C6 –> C7 –> C8 –> C9.
1) Opsonisation - C3b is an opsinin so recruits macrophage as it has C3b receptor –> phagocytosis by macrophage or exocytosis by neutrophil
2) Membrane attack complex - C5b -> C9 come off and form MAC which attaches onto pathogen surface and encourages lysis
3) Chemotaxis by C3a and C5a
What are the different types of interferons?
alpha, beta and gamma
alpha and beta - grouped together and produced by tissue cells
gamma - usually produced by immune cells.
What is the mechanism of activation of interferon alpha and beta?
what are their effects?
- host cell infected with virus
- IRF transcription factor activated to produce interferons alpha and beta
- alpha and beta interferons released into plasma/system
EFFECTS
1. alert nearby tissues/healthy cells to stimulate production of protein kinase R (anti-viral peptides) to destroy virus
2. activates natural killer cells to initiate apoptosis of infected host cells
What is the structure of a toll-like receptor? Are they part of the adaptive or innate immune system?
single membrane-spanning non-catalytic receptors
Part of the adaptive immune system.
Which is the most abundant antibody? Where are they predominantly located.
IgG, 65-70% in the blood plasma and produced by plasma cells.
What are the primary mechanisms of IgG?
IgG is GREAT at binding.
Secreted much more in the secondary immune response.
- Initiate complement cascade which enhances opsonization and MAC
2.neutralises viral proteins on their surface preventing their binding and infection of host cells
- binds to free antigen to trigger precipitation (antigen/antibody complexes) to trigger opsonisation and phagocytosis
- placental production of IgG to encourage passive immunity for baby - involved in haemolytic disease of the newborn.
What is the structure of IgA antibody vs IgG antibody?
IgA - dimer (joined by J chain when secreted, monomer in circulation)
IgG - monomer
Where is IgA primarily located? (4)
- Sweat
- Saliva
- Mucosal lining of GI tract
- Milk (lactation)
Responsible for mucosal immunity.
What is the structure of IgM antibodies?
IgM has MANY binding sites.
Pentamer or monomeric.