Physiology of immunology Flashcards
1
Q
What are the 4 mechanisms by which neutrophils can destroy organisms
A
- “Respiratory burst”: activation of NADPH oxidase complex and production of H2O2 and OCl- in phagosome or extra-cellular space
- Enzymatic destruction: fusion of lysosome with phagosome (-> phagolysosome)
- Degranulation: release of anti-microbial enzymes into the extra-cellular environment
(can be combined as “enzymatic destruction” but happens in extra-cellular matrix rather than in phagosome) - Release of neutrophil extracellular traps (NETs): core DNA with multiple proteins (histones, proteases) able to destroy extracellular organisms
2
Q
What cells are sentinel cells
A
- Mast cells
- Dendritic cells
- Macrophages
–> initiate inflammatory response
3
Q
What eicosanoids can be produced from arachidonic acid
A
- Leukotrienes by lipoxygenase
- Prostaglandins, thromboxane, prostacyclins by cyclooxygenase
4
Q
What is a major mechanism of destruction of organisms by macrophages
A
Activation of NO synthase -> generates NO from arginine -> reacts with superoxide anion to form nitrogen dioxide radicals
5
Q
What is the definition of an acute phase protein
A
Protein whose serum concentration increases by more than 25% in response to pro-inflammatory cytokines
6
Q
Name some positive and negative acute phase proteins. Which are the most important in the cat and in the dog
A
Positive
- C-reactive protein (CRP)
- Serum amyloid A (SAA)
- Haptoglobin
- Ceruloplasmin
- Alpha2-macroglobulin
- Fibrinogen
- Alpha1-acid glycoprotein (AGP)
- Complement proteins (C3, C4)
- Lipopolysaccharide binding protein (LPB)
Negative
- Albumin
- Transferrin
- Retinol-binding protein
- Adiponectin
Cat: SAA most important, followed by AGP and haptoglobin
Dog: CRP and SAA most important, followed by haptoglobin, AGP, ceruloplasmin
7
Q
What is the time required for establishment of the adaptive immune response at an injury site
A
4-7 days
8
Q
What characteristics of epithelial barriers allow defence against micro-organisms
A
- Movement (airway muco-ciliary escalator, GI peristalsis)
- Secretion of antimicrobial substances (enzymes, immunoglobulins)
- Microflora
- Presence of epithelial macrophages
9
Q
What globulins are the antibodies? What is their molecular composition?
A
- Immunoglobulins = gamma-globulins
- Made of 2 heavy chains and 2 light chains, which each have a variable portion at the N-terminal segment (->antigen binding site, Fab region) and a constant portion at the C-terminal segment (-> Fc region)
10
Q
What are the immunoglobulin classes and their main different functions / locations? What is the molecular difference between them?
A
They have different heavy chains
- IgA -> dimer mostly in mucosal secretions, prevents attachment of micro-organisms to mucosal surfaces
- IgD -> only on naive B lymphocytes
- IgE ->found in circulation and on mast cells, key to type I hypersensitivity
- IgG -> monomer found in serum, main actor of secondary immune response (opsonization)
- IgM -> polymer found in serum, important in primary immune response, actor of agglutination
11
Q
What can activate the complement
A
- Classical pathway:
- Direct binding of C1 to an antigen
- Binding of C1 to C-reactive protein
- Binding of C1 to an antigen-antibody (IgG or IgM) complex - Lectin pathway:
- Mannose binding protein - Alternate pathway:
- Presence of a “trigger-surface” (bacteria, PAMPs, DAMPsetc.)
- Bacterial endotoxin
12
Q
What is the endpoint of the complement pathways
A
Formation of the membrane attack complex (MAC)
13
Q
What are the biological consequences of complement activation
A
- Cytolysis of target micro-organism / cell due to formation of membrane attack complex (MAC)
- Generation of bioactive substances -> anaphylatoxins and chemoattractants leading to vasodilation, increased endothelial permeability, mast cell degranulation, and chemotaxis
- Enhancement of phagocytosis by neutrophils and macrophages (chemotaxis to site of infection or opsonization for phagocytosis in liver or spleen)
- Interaction with other inflammatory pathways
- Enhancement of coagulation: induction of TF and PAI-1
14
Q
What are the most important proteins of the complement
A
C3a and C5a
15
Q
What are the components of the innate and adaptive immune responses
A
- Innate immune response:
- Neutrophils
- Macrophages
- Complement
- Natural Killer cells
- Secreted (polyreactive) antibodies
- Epithelial barriers
- Secreted enzymes
- Dendritic cells - Adaptive immune response:
- T lymphocytes
- B lymphocytes
- Plasma cells
- Specific antibodies
16
Q
Where is the largest proportion of lymphoid tissues found
A
In the intestinal mucosa (GALT = gastro-intestinal associated lymphoid tissue)
17
Q
What are the primary lymphoid tissues and secondary lymphoid tissues
A
- Primary lymphoid tissues:
- Bone marrow
- Thymus - Secondary lymphoid tissues:
- Encapsulated tissues = lymph nodes and spleen
- Unencapsulated tissues = mucosal lymphoid aggregates (MALT = mucosa associated lymphoid tissue)
18
Q
What cells are antigen-presenting cells? Name antigen presenting cells of the epidermis and the liver
What cells recognize the presented antigen?
A
- Dendritic cells (Langherans cells in the skin) - most important
- Macrophages (Kupffer cells in the liver)
- B lymphocytes
T lymphocytes recognize the antigen (helper T cells when presented with MHC II and cytototoxic T cells when presented with MHC I)
19
Q
Give 3 examples of pattern recognition receptors and the PAMPs to which they bind
A
Toll-like receptors:
- TLR-2 -> peptidoglycan (from Gram + bacteria) + zymosan from yeast
- TLR-4 -> LPS (from Gram - bacteria)
- TLR-3 -> viral RNA
(- TLR-5 -> bacterial flagellin - TLR-9 -> bacterial DNA)
20
Q
What are the 2 types of T lymphocytes? What CD (cluster of differentiation) do they express and what type of MHC (major histocompatibility complex) to they interact with
A
- Helper T cells -> CD4, interact with MHC class II
- Cytotoxic T cells -> CD8, interact with MHC class I
- Also suppressor T cells - suppress function of cytotoxic and helper T cells –> prevention of excessive immune reaction (mainly CD4+ T cells)
21
Q
Between the T helper lymphocytes Th1 and Th2, which ones have a preferential role in cell-mediated immunity vs humoral immunity
A
- Th1 in cell-mediated immunity
- Th2 in humoral immunity
22
Q
How can cytotoxic T lymphocytes induce cytolysis
A
- Secretion of perforins next to the target cell
- perforins punch round holes in the membrane of the attacked cell –> fluid flows rapidly into the cell from the interstitial space
- Induction of apoptosis of the target cell by TNF-alpha or the Fas ligand
23
Q
Where does the selection / maturation of T lymphocytes happen? What are the 2 phases?
A
In the thymus
Phase 1 = positive selection -> only keep T cells that have a T-cell receptor (TCR) able to interact with the MHC of an antigen presenting cell
Phase 2 = negative selection -> only keep T cells that have a TCR that does not have a strong affinity for auto-antigens
24
Q
What cells are required for the maturation of B lymphocytes into plasma cells
A
T helper lymphocytes that recognized the same antigen (usually Th2)
(Rarely, antigens can be T independent and Th cells are not required then)
25
In response to an antigen, which antibody (type of immunoglobulin) is secreted first? Which will persist for longer?
IgM is secreted first, then IgG
IgG persists in time
26
What are the main inflammatory / anti-inflammatory cytokines
1. Inflammatory:
- IL-6
- IL-1
- TNF-alpha
- IFN-gamma
- IL-2
2. Anti-inflammatory:
- IL-10
- TGF-beta
- IL-4
27
What are the actions of histamine
- H1 receptors: smooth muscle contraction and endothelial changes leading to vasodilation and increased permeability + bronchoconstriction + decreased inotropy
- H2 receptors: stimulation of gastric acid secretion and regulation of cardiac myocytes
- H3 and H4: neurotransmitter release (decreased norepinephrine), modulation of immune response with chemokines and cytokines
28
Describe the arachidonic acid cascade
- COX pathway: arachidonic acid -> PGH2 -> PGE2, PGD2, PGI2 (= prostacyclin), thromboxane A2
- LOX pathway: arachidonic acid -> leukotriene
29
What is the name of the major lymphoid tissue of the GI tract? What cells are mostly found in it?
Peyer's patches
Contain:
- B lymphocytes
- T lymphocytes
- Antigen presenting cells = dendritic cells, macrophages, epithelial M cells
30
What are 3 ways antibodies can participate in host defence
- Opsonization: coating of pathogens (by IgG and C3b) to facilitate phagocytosis
- Neutralization: binding of antibodies to pathogens prevents them to infect other cells -> good for viruses
- Activation of complement: leads to cytolysis or activation of other inflammatory pathways
31
What endothelial glycoproteins are important to allow neutrophil diapedesis
- Selectins
- ICAM-1 (= inter-cellular adhesion molecule)
32
What cytokines activate macrophages
IFN-gamma (++), TNF-alpha, IL-2
33
What is an important chemokine for recruitment of neutrophils
IL-8
34
What is a major cytokine for induction of fever? By what mechanism?
IL-6 -> induction of COX-2 in hypothalamus -> PGE-2 production -> alteration of thermostatic set point
35
Where do B lymphocytes and T lymphocytes develop
B lymphocytes in bone marrow, Peyer's patches
T lymphocytes in thymus
36
Between CD19 and CD3, which one is carried by B lymphocytes / T lymphocytes
CD19 on B lymphocytes
CD3 on T lymphocytes
37
Where are B lymphocytes found in the body
- Cortex of lymph nodes
- Marginal zone of spleen
- Peyer's patches
- Bone marrow
38
What is required for activation of a B cell
- Recognition of antigen by BCR (B-cell receptor)
- Co-stimulation by a helper T cell recognizing the same antigen and secreting cytokines
39
Name 3 pathways leading to cytokine release
- Binding of antigens to TCR on T cells (+ BCR on B cells)
- Binding of PAMPs or DAMPs to PRR (pattern recognition receptors) of sentinel cells
- Binding of antibodies to Fc receptors on phagocytes
40
What cytokine is responsible for differentiation of eosinophils
IL-5
41
Which MHC pathway is more for endogenous / exogenous antigens in antigen presenting cells
- MHC I for endogenous antigens (-> viruses)
- MHC II for exogenous antigens
42
Which of macrophages or neutrophils is considered the first line of defence to inflammation? Second line?
- Macrophages are the first line (within minutes - already present in various tissues)
- Neutrophils are the second line (within hours)
3rd line: second invasion of macrophages into the tissue
4th line: greatly increased production of both granulocytes and monocytes by the bone marrow.
43
What is a histiocyte?
Macrophages present in the skin and subcutaneous tissues
44
What are 3 mechanisms by which neutrophils are called to an inflamed area?
Inflammatory cytokines (TNF, IL-1) initiate:
1. Margination: increased expression of adhesion molecules, such as selectins and intracellular adhesion molecule-1 (ICAM-1) on the surface of endothelial cells --> react with integral on neutrophil --> Neutrophils stick to the capillary wall
2. Diapedesis: loosened intracellular attachments between endothelial cells
3. Chemotaxis: substances (bacterial/viral toxins, degenerative products of inflamed tissues, complement, coagulation) cause a concentration gradient promoting movement of neutrophils towards source of inflammation
45
5 factors responsible for control of macrophage response to inflammation and increased production of granulocytes and monocytes by the bone marrow
- TNF
- IL-1
- GM-CSF (granulocyte-monocyte colony-stimulating factor)
- G-CSF (granulocyte colony-stimulating factor)
- M-CSF (monocyte colony-stimulating factor)
46
Name circulating factors leading to the release of neutrophils from the bone marrow
1. Cytokines
- G-CSF (granulocyte colony stimulating factor)
- GM-CSF (granulocyte macrophage colony stimulating factor)
- TNF-alpha
- TNF-beta
2. Complement (C5a)
47
What is the proportion of circulating vs marginated neutrophils in dogs and cats
Dogs: 50% circulating, 50% marginated
Cats: 25% circulating, 75% marginated
48
What is pus composed of?
Varying portions of necrotic tissue, dead neutrophils, dead macrophages, and tissue fluid.
After the infection has been suppressed, autolyses of these cells and eventually absorbed into the surrounding tissues and lymph
49
Why are eosinophils present in tissues where allergic reactions occur?
Mast cells and basophils, which participate in allergic reactions, release eosinophil chemotactic factor --> migration of eosinophils to tissue
Eosinophils are believed to detoxify some of the inflammation-inducing substances released by the mast cells and basophils and probably also to phagocytize and destroy allergen- antibody complexes
50
Name 4 substances released by mast cells that participate in anaphylaxis
- Histamine
- Bradykinin
- Heparin
- Serotonin
51
What differentiates B-lymphocytes from T-lymphocytes?
B lymphocytes
- Produced in bone marrow (vs thymus for T lymphocytes)
- B lymphocytes = humoral immunity (vs cell-mediated immunity)
- Secrete antibodies that are the reactive agents (vs T lymphocyte: whole cell developing reactivity against the antigen via surface receptor protein)
- Have even greater diversity than the T lymphocytes
Both migrate to lymphoid tissues after processing
52
Describe the difference between the antibody response to a primary antigen exposure vs subsequent exposure
Some lymphoblasts
Primary response: 1-week delay in appearance, weak potency, and short life
Secondary response: begins rapidly after exposure to the antigen (often within hours), is far more potent, and forms antibodies for many months rather than for only a few weeks.
--> Thanks to the presence of memory cells (B-lymphocytes formed from lymphoblasts from first exposure)
53
What are the 2 mechanisms of action of antibodies?
1. Direct attack on the invader
- Agglutination
- Precipitation
- Neutralization
- Lysis
2. Activation of the complement (which provides most of the protection)
54
Name 7 effects of the complement system (classic pathway) that help to prevent damage to the body’s tissues caused by the invading organism or toxin.
1. Opsonization and phagocytosis
--> C3b strongly activates phagocytosis by neutrophils and macrophages
2. Lysis
--> rupture of cell membranes of bacteria by C5b6789
3. Agglutination
--> complement products change the surfaces of the invading organisms, causing them to adhere to one another
4. Neutralization of viruses
--> attack the structures of some viruses making them nonvirulent
5. Chemotaxis
--> C5a initiates chemotaxis of neutrophils and macrophages
6. Activation of mast cells and basophils
--> C3a, C4a, C5a. Release of histamine, heparin, bradykinin --> increased local blood flow, increased leakage of fluid and plasma protein into the tissue
7. Inflammatory effects
--> further increase in blood flow, capillary leakage of proteins, coagulation in tissue space preventing movement of pathogens
55
7 lymphokines secreted by T-helper cells and what are their roles?
- IL-2
- IL-3
- IL-4
- IL-5
- IL-6
- GM -CSF
- Interferon-γ
- Stimulation of growth and proliferation of cytotoxic T-cells & suppressor T-cells (IL-2)
- B-cell growth and differentiation to form plasma cells and antibodies (IL 4-5-6)
- Activation of macrophage system
- Feedback stimulatory effect on the T cells themselves (IL-2)
56
5 cardinal signs of inflammation
Pain
Redness
Heat
Swelling
Loss of function of the affected tissue
57
Properties of a substance that increase antigenicity
- Foreign to the host
- Molecular mass >10 kD.
- Particulate or aggregated (small soluble molecules are poorly antigenic)
- Complex (tertiary) molecular structure.
- Carry a charge
- Chemically complex
- Biologically active
58
Describe the molecular structure of a immunoglobulin
Comprised of four glycoslyated protein chains (2 heavy and 2 light) held together by interchain disulphide bonds in a Y-shaped conformation
59
What is the complement?
A series of approximately 30 plasma proteins which, once activated, interact sequentially, forming a self- assembling enzymatic cascade and generating biologically active molecules mediating a range of end processes that are significant in the immune and inflammatory response.
60
Normal cells have ptrotes that help protect against the complement by disrupting the C3 convertase. What are the proteins?
- Decay accelerating factor (DAF)
- Complement receptor 1 (CR1)
- Membrane co-factor protein (MCP)
61
What are the 4 pathways of the complement?
- Classic & Lectin pathway
- Alternative pathway
- Terminal pathway
62
Which molecules of the complement are also known as anaphylatoxins or chemoattractants and what are their mechanisms in inflammation?
C3a (more abundant) & C5a (more potent)
- Mediate vasodilation --> oedema
- Mast cell degranulation
- Smooth muscle contraction
- Neutrophil activation
- Formation of chemotactic gradient
63
True or false: the spleen has no lymphatic drainage
True
64
What is a hypersensitivity reaction?
Involves sensitization to an antigen by prior exposure (often repeated and over time). Once an individual is sensitized, subsequent re-exposure to that antigen may lead to an inappropriately excessive immune response.
65
What are the 4 types of hypersensitivity reactions?
- Type I or immediate (or IgE-mediated) hypersensitivity - antibody mediated
- Type II or antibody-mediated cytotoxic hypersensitivity - antibody mediated
- Type III or immune complex hypersensitivity - antibody mediated
- Type IV or delayed-type hypersensitivity (DTH) - cell mediated
66
Describe the pathophysiology of type I hypersensitivity reaction. What are some examples?
First phase: sensitization
- Antigen encountered at the mucosal or cutaneous surface
- Antigen presenting cell migrates to lymphoid tissue and signals CD4+ T cel to differentiate to a Th2 cell
- Humoral immune response
- B-cells
- Generation of antigen specific IgE which bind to mast cells and basophils
- No clinical signs
Second phase: re-encounter of antigen
- Absorbed antigen meets the IgE-coated mast cells
- The antigen is bound by at least 2 IgE --> cross-linking antibodies and initiating a signalling pathway within that mast cell
- Mast cell degranulation, release of pro-inflammatory cytokines --> vasodilation, bronchoconstriction, pruritic
Late phase response (4-24h)
- Recruitment of eosinophils and macrophages
Ex: asthma, food allergies, skin allergies, parasitic disease
67
What is type II hypersensitivity characterized by and what are some examples?
- Destruction of a target cell and sensitization is to an antigen displayed on the surface of that target
- Sensitization leads to production of IgG (mostly) or IgM antibodies that may bind to target cells and cause their destruction via complement (MAC) or macrophage phagocytosis
Ex: Hemolytic transfusion reaction, autoimmune diseases (IMHA, ITP, myasthenia gravis)
68
Which antibodies are involved in the immune humoral response to bacterial infection? What are their roles in this context?
- IgG: neutralization of toxins + opsonization and permits complement mediated lysis
- IgA: secreted to the luminal surface where they may interfere with the interaction of organism with receptor molecules
69
List 5 functions of the spleen
- Filtering of microorganisms and antigenic particles from the blood
- Synthesis of IgG and cytokines of the complement pathway
- Maturation of newly formed erythrocytes
- Storage of RBCs and platelets,
- Removal of abnormal and senescent RBCs
70
What cells express PRRs
Macrophages, neutrophils, dendritic cells, platelets, NK lymphocytes, and some others (fibroblasts, some intestinal epithelial cells)
71
Name 4 types of PRRs
1. Membrane-bound PRRs:
- Toll-like receptors (TLRs) -> surface or endosomal
- C-type lectin receptors (CLRs)
2. Cytoplasmic PRRs
- Nucleotide oligomerization domain (NOD)-like receptors (NLRs)
- Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs)
72
What are some detrimental effects of NETs
- Stimulation of thrombosis (activation of platelets via TLR-2 and TLR-4, inhibition of protein C, activation of factor XII, inhibition of tPA, inhibition of TFPI)
- Histones recognized as DAMPs and promote inflammation
- Oxidative damage due to production of ROS
73
What molecule present on leukocytes is required for adhesion (tethering) of neutrophils to the endothelium before diapedesis
Leukocyte function associated antigen-1 (LFA-1) -> binds to Intercellular adhesion molecule-1 (ICAM-1)
74
How can platelets activate leukocytes
- Activated platelets express P-selectin on their surface -> binds to P-selectin glycoligand on neutrophils and activates NETosis
- Activated platelets also secrete HMGB-1 (high mobility group box 1) which is a PAMP
