APPP 10 and 12: Body Defense System Flashcards
What are the 5 properties of the immune system?
- mobility
- replication
- specificity
- memory
- diversity
Properties of the Immune System
Mobility
systemic protection against localized insults through rapid cell migration to infected area
Properties of the Immune System
Replication
immune response is amplified through clonal expansion and signaling cascade
Properties of the Immune System
Specificity
prevent recognition of non-cross-reacting antigens and identify self vs. non-self
Properties of the Immune System
Memory
faster and stronger response to (similar) subsequent infection
Properties of the Immune System
Diversity
combinatorial library of antigen receptors to recognize innumerable pathogens
What are the primary lymphoid organs of the immune system?
- thymus
- bone marrow
What are the mucosal lymphatic tissues of the immune system?
- tonsils and adenoids
- appendix
- Peyer’s patches
What are the other organs of the immune system?
- lymph nodes
- spleen (gigantic lymph node)
What is the lymphatic system?
circulation system of lymphatic vessels
How does the immune system monitor all parts of the human body?
through the circulation system and the system of lymphatic vessels
- cells and fluids are exchanged between blood and lymphatic vessels, enabling the lymphatic system to monitor the body for invading microbes
Where are lymph nodes located?
- sit along the lymphatic vessels, with clusters in the neck, armpits, abdomen, and groin
What does each lymph node contain?
each node contains specialized compartments where immune cells congregate and encounter antigens
How many lymph nodes are in the human body?
500-600
What are the 4 functional areas of lymph nodes?
- cortex
- germinal centre
- para-cortex
- medulla
What does the cortex of lymph nodes do?
contains unactivated mature T cells
What does the germinal centre of lymph nodes do?
contains activated B cells → plasma cell development and antibody affinity maturation
What does the para-cortex of lymph nodes do?
contains a mix of unactivated and activated mature T cells
What does the medulla of lymph nodes do?
funnels to collect mature immune cells and antibodies for distribution to lymphatic/blood circulation
What is innate immunity?
first, rapid, short-term responses to a broad range of microbes – direct pathogen identification
- external defenses
- internal defenses
What are the external defenses of innate immunity?
- skin
- mucous membranes
- secretions
What are the internal defenses of innate immunity?
- phagocytic cells
- antimicrobial proteins
- inflammatory response
- natural killer cells
What is adaptive/acquired immunity?
slower responses to specific microbes (activated by, and responds to, innate immunity) – specialized and adaptable to a single type of invader, recognize invaders inside host cells, and able to recall encounters
- humoral response (antibodies)
- cell-mediated response (cytotoxic lymphocytes), with help from APC
Innate vs. Adaptive Immunity
Specificity
- innate: limited and fixed
- adaptive: extensive
Innate vs. Adaptive Immunity
Memory
- innate: none
- adaptive: yes
Innate vs. Adaptive Immunity
Time to Response
- innate: hours
- adaptive: days
Innate vs. Adaptive Immunity
Soluble Factors
- innate: lysozymes, complement, C-reactive protein, interferons, mannose-binding lectin, antimicrobial peptides
- adaptive: antibodies, cytokines
Innate vs. Adaptive Immunity
Cells
- innate: neutrophils, monocytes, macrophages, natural killer cells, eosinophils
- adaptive: B lymphocytes, T lymphocytes
Describe the specificity of innate immunity.
non-antigen specific
- uses pre-existing limited library of receptors (pattern recognition receptor) – ie. toll-like receptors (TLRs)
- recognition of highly conserved structures (pathogen-associated molecular patterns or PAMPs) – those essential to microorganism survival or pathogenicity (such as LPS and mannose)
- equal response to a range of organisms
What are the cellular mediators of innate immunity? (8)
blood:
- neutrophils
- eosinophils
- monocyte
- natural killer cells
- basophils
peripheral tissues:
- macrophage
- dendritic cells
- mast cells
What do neutrophils do?
ingest (phagocytotic) and destroy
What do eosinophils do?
release toxic molecules and destroy
What do monocytes do?
ingest, destroy, and antigen presentation
What do natural killer cells do?
kill cancer or viral-infected host cells
What do basophils do?
release first chemicals that start inflammation
What do macrophages do?
ingest, destroy, and antigen presentation
What do dendritic cells do?
ingest, recruit others, and antigen presentation
What do mast cells do?
release first chemicals that start inflammation
Tissue-Specific Types of Monocytes
Brain
microglial cells
Tissue-Specific Types of Monocytes
Lung
alveolar macrophages
Tissue-Specific Types of Monocytes
Liver
Kupffer cells
Tissue-Specific Types of Monocytes
Kidney
mesangial phagocytes
Tissue-Specific Types of Monocytes
Lymph Node
resident and recirculating macrophages
Tissue-Specific Types of Monocytes
Spleen
macrophages
Tissue-Specific Types of Monocytes
Blood
monocytes
Tissue-Specific Types of Monocytes
Bone Marrow
precursors
Tissue-Specific Types of Monocytes
Joint
synovial A cells
Where are macrophages located?
in every tissue
- some macrophages circulate in the blood and migrate with rapid response to insults in tissues
Describe the structure and lifespan of macrophages.
- morphology is amoeboid-like
- inactive lifespan: months to years
- active lifespan: days to weeks
What are the functions of macrophages (3)
- phagocytosis
- antigen presentation (APC)
- initiation of tissue repair
Where are dendritic cells located?
- immature: in blood and tissues – generally located in tissues interfacing with the outside (ie. skin, nose, lungs, stomach)
- mature: activated cells move to lymph nodes – interact with T cells and B cells
What are the functions of dendritic cells? (4)
- phagocytes
- antigen-presenting cells
- activate adaptive immune response
- regulate T-cell activation
What are the specific functions of adaptive/acquired immunity? (5)
- recognizes ‘non-self’ when ‘self’ is present
- antigen-specific and clonal
- each clonal population recognizes only one type of antigen
- eliminates pathogens and infected cells
- generates immunological memory
Describe the development of B cells.
- form and mature in bone marrow
- classes: memory B cell, plasma cell
Describe the development of T cells.
- produced in bone marrow
- mature in thymus
- classes: helper, cytotoxic, memory, regulatory
Helper T Cell
- assist other immune cells with maturation/activation
- enhance or suppress immune cell actions
- recognize signal from antigen-presenting cells (binds to MHC II)
- CD4+ co-receptor – activates cytotoxic T cells and B cells
- 70% of all T cells
Memory T Cell
- coordinate rapid response to re-infection with same agent
- proliferate when reintroduced to antigen
- CD4+ or CD8+ co-receptor
Cytotoxic T Cell
- kill altered or infected cells
- recognized infected cells (binds to MHC I)
- CD8+ co-receptor – activation induces release of cytotoxic molecules
- around 25% of all T cells
T Regulatory Cell
- suppress and regulate auto-reactive T cells
- T cell receptor
- CD4+
- CD25
What do T cells do?
activity against infected host cells (inaccessible to antibodies)
- bacteria, viruses, fungus, parasites, cancer, transplants
- no antigen-presenting property
Memory B Cell
initiate rapid response to re-infection with same agent
- allow for a stronger and faster immune response next encounter
Plasma B Cell
neutralize toxins and viruses, opsonize bacteria
- antibody production
Describe the receptors of B lymphocytes.
each B lymphocyte produces only one type of antigen receptor
What can activated B cells do?
can act as APC to activate helper T in the classical B cell activation pathway
Interplay Between Innate and Acquired Immunity
- co-activation of B cells through BCR and TLR
- antigen presentation by macrophage
- complement proteins
- cytokines (ie. interferons, TNF, IL1
Severe COVID
What does a reduction or dysfunction in the adaptive immune response lead to? (4)
- over-activity of the innate system
- exaggerated cytokine response
- compromised normal immune functions
- coagulation dysfunctions and other organ system failures
What is inflammation?
acute (immediate) response to tissue injury and immune activation
- mediated by the innate immune system
- cross-talk and signaling through the release of cytokines and inflammatory chemicals/hormones
Mediators of the Inflammatory Response
Pre-formed vs. Newly Synthesized Mediators (Slide 36)
-
Protein Mediators of the Immune Response
Proteins and Polypeptides (Slide 37)
-
Protein Mediators of the Immune Response
What are cytokines?
protein signaling molecules
Protein Mediators of the Immune Response
What are the 5 types of cytokines?
- interferons
- chemokines
- interleukins
- TNF 𝛼
- growth factors
Protein Mediators of the Immune Response
What is the function of interferons?
involved in innate antiviral response
- type I (𝛼, 𝛽)
- type II (𝛾)
Protein Mediators of the Immune Response
What is the function of chemokines?
chemotaxis proinflammatory – mediate chemoattraction/chemotaxis between cells
- MCP-I
- IL-8
- etc.
Protein Mediators of the Immune Response
What is the function of interleukins?
leukocyte development – acts on leukocytes, various functions
- IL-6
- IL-10
- etc.
Protein Mediators of the Immune Response
What is the function of TNF 𝛼 (tumour necrosis factor family)?
regulate immune and inflammation response
- acute phase response
- coagulation
Protein Mediators of the Immune Response
What is the function of growth factors?
growth differentiation – blood cell production,
- VEGF
- GM-CSF
- TGF 𝛽 – regulation of immunity and wound healing
- etc.
Protein Mediators of the Immune Response
Describe the composition of cytokines.
- soluble proteins, peptides, or glycoproteins
- picomolar (10^-12) or 0.000,000,000,000,1 mol/L
- significant roles in inflammatory response – function as both pro- and anti-inflammatory molecules
Chemical and Hormonal Mediators of the Immune Response
Amino Acids and Lipids (Slide 40)
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Chemical and Hormonal Mediators of the Immune Response
Describe these mediators.
- signaling molecules activated or released by immune cells as well as injured cells
- mediate inflammatory responses
Chemical and Hormonal Mediators of the Immune Response
What are the 3 types of mediators?
- amino acid derivatives: histamine, serotonin
- lipid derivatives: prostaglandins, leukotrienes (both are eicosanoids)
- hormones and other neurotransmitters: bradykinin, substance P
Chemical and Hormonal Mediators of the Immune Response
What is histamine derived from and what is its main source?
- derived from amino acid histidine
- produce, store, and release mainly from mast cells
- also from basophils
Chemical and Hormonal Mediators of the Immune Response
What is the function of histamine?
vasodilation and increase permeability
- serves important roles in immune responses and inflammation process
- binds to and activates GPCRs (H1 to H4 tissue-specific subtypes)
Chemical and Hormonal Mediators of the Immune Response
What is serotonin derived from and what is the main source?
- derived from amino acid tryptophan
- produced by enterochromaffin cells and stored mainly in platelets
Chemical and Hormonal Mediators of the Immune Response
What is the function of serotonin?
vasodilation, increase permeability, pain, fever
- neurotransmitter serves multiple functions in homeostasis (GI, CNS, and body defence)
- binds to and activates GPCRs (5HT1 to 7 tissue- and function-specific subtypes
Lipid Mediators of the Humoral Immune Response
How are eicosanoids synthesized?
synthesized with arachidonic acids (diet + cell/nuclear membrane
Lipid Mediators of the Humoral Immune Response
What are eicosanoids?
lipid mediators
Lipid Mediators of the Humoral Immune Response
Describe the structure of eicosanoids.
- made by oxidation of omega-6 fatty acids
- 20 carbons, 4 double bonds
- biosynthesis by cyclo-oxygenase (prostagalndins) or lipo-oxygenase (leukotrienes)
Lipid Mediators of the Humoral Immune Response
What are the 3 main mediators?
- prostaglandins
- leukotrienes
- platelet activating factor
Lipid Mediators of the Humoral Immune Response
What is the main source of prostaglandins?
mast cells, leukocytes
Lipid Mediators of the Humoral Immune Response
What is the function of prostaglandins?
vasodilation, pain, fever
Lipid Mediators of the Humoral Immune Response
What is the main source of leukotrienes?
mast cells, leukocytes
Lipid Mediators of the Humoral Immune Response
What is the function of leukotrienes?
increase permeability, leukocyte adhesion, chemotaxis
Lipid Mediators of the Humoral Immune Response
What is the main source of platelet activating factor?
leukocyte, mast cells
Lipid Mediators of the Humoral Immune Response
What is the function of platelet activating factors?
vasodilation, increase permeability, leukocyte adhesion, chemotaxis
What are eicosanoids essential for?
- essential for control of inflammation and immunity
- synthesized upon activation signals
- specific inhibition of the major biosynthesis enzymes is a major mechanism to control inflammation
Eicosanoids
What is the function of prostacyclin?
vasodilation
Eicosanoids
What is the function of prostaglandin D/E?
vasodilation
Eicosanoids
What is the function of thromboxane A2?
vasoconstriction
Eicosanoids
What is the function of leukotrienes C/D/E?
vasoconstriction
Eicosanoids
What is the function of leukotrienes C/D/E?
vascular permeability
Eicosanoids
What is the function of prostaglandin D?
vascular permeability
Eicosanoids
What is the function of leukotriene B?
chemotaxis and leukocyte adhesion
Eicosanoids
What is the function of HETE?
chemotaxis and leukocyte adhesion
Eicosanoids
What is the function of leukotrienes C/D/E?
bronchoconstriction
Eicosanoid Functions
(Slide 46)
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What are major histocompatibility compexes (MHCs)?
present as a peptide epitope on surface of cell
- polymorphic – around 2000+ alleles
- co-dominant – express both allele equally
- polygenic – 6 major MHC loci plus minor loci
What are the functions of major histocompatibility complexes (MHCs)?
play essential roles in immune system engagement
- recognition of self from non-self
What are the properties of MHC I?
- present on all nucleated cells and platelets
- display infectious epitopes from hijacked cells’ synthesis of infectious agent (non-self) that are recognized by cytotoxic T cells
What are the properties of MHC II?
- present on antigen-presenting immune cells – macrophages, dendritic cells, and B cells
- display degraded/digested pathogen epitopes that are recognized by helper T cells
What role do cytotoxic T cells play in antigen recognition?
- cytotoxic T cell (CD8+) receptor recognizes MHC I markers
- special breaks to ensure a regulated immune activation (CTLA4 and PD1 receptors)
What role do helper T cells play in antigen recognition?
- helper T cell (CD4+) receptor recognizes MHC II markers
- special breaks to ensure a regulated immune activation (CTLA4 and PD1 receptors)
T-Cells Antigen Recognition Diversity – Genetic Recombination of the T Cell Receptor (TCR)
(Slide 51)
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Describe the structure of T cell receptors.
- T cell receptor consists of an alpha and a beta chain (subunits)
- each subunit is generated through recombination of 1 segment each from the V and j loci (alpha) and V, D, and J loci (beta)
- generates immunological diversity, as each mature T cell will have a different combination of subunits that recognize different antigens
How does T cell specificity occur?
positive and negative selection in thymus during development/maturation
- positive selection of affinity for MHC I or MHC II (antigen-presenting cell surface molecules) with either the CD4 or CD8 receptors – MHC not recognized, therefore apoptosis
- negative selection of cells that recognize self antigens – cannot be autoreactive
- 2% survival
Describe the functional diversity of T cells.
same TCR (progeny of a single T cell), different functional role through cytokines-directed differentiation
Describe the diversity of B cell receptors (BCR).
- each mature B cell is covered with a single type of BCR
- BCRs are predecessors of an antibody that recognized one antigen
- two identical binding sites on each fork of the Y
- BCR can bind antigen directly in the absence of co-receptors
- B cells with BCR that recognizes self antigens are destroyed (central and peripheral tolerance)
Antigen Recognition Diversity – VDJ Genetic Recombination
(Slide 58)
- gene components scattered through one chromosome
- rearranged gene components encoding a heavy chain
- assembled BCR molecule
Describe the steps of the T-cell dependent pathway of B-cell activation.
- antigen binding to BCR
- internalization and MHC II presentation to T helper cells
- T helper cell release cytokines
- activated B cell differentiates into plasma cells for antibody production and memory B cells