HTHSCI 3I03 Study Guide - Final Guide: Acute-Phase Protein, Adaptive Immune System, Chemokine Receptor
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INNATE IMMUNITY IV
(local inflammation and the initiation of adaptive immunity)
Local inflammation
When it happens: If pathogen has crossed intrinsic barriers and
defeated initial immune cell killers, we will induce inflammation
to recruit more cells and amp up the innate response and start to
activate the adaptive immune response
• Importance for fighting infection
o Increases in local and systemic temperature
▪ Lots of pathogens cannot survive in
high temperatures
▪ Macrophages and APCs are actually
more effective at higher temperatures
o Delivers additional effectors, molecules and
cells to the site of infection
o Provides a physical barrier preventing further
spread of infection
▪ Lots of plasma from capillaries.
Fibrinogen and clotting physically
entraps pathogens to prevent
spreading
o Is essential for induction of adaptive immunity
• Characteristics
o Redness, heat, swelling, pain
The process of inflammation
How do immune cells know where to go and how do they get
there?***
• Adhesion molecules: addressins (they are tags that are
posted at the site of infection, expressed on endothelial
cells)
o Selectins (p-selectin, expressed on endothelial
cells)
o Integrins (LFA-1, expressed by leukocytes)
o Ig family (ICAM-1, expressed on endothelial
cells)
o LFA-1 and ICAM-1 interact with each other
during inflammation
• Directions: chemotactic substances/signals + gradient
o Leukocytes move towards concentrations of
chemokines via their chemokine receptors
***The process of leukocyte migration to sites of infection
• Rolling adhesion (as mentioned earlier)
o S-Le^x on leukocyte and E-selectin on
endothelial cell
• Tight binding (as mentioned earlier)
o LFA-1 on leukocyte and ICAM-1 on
endothelial cell
• Diapedesis
o Conformational change to endothelial cells
allow entry of leukocyte to the site of infection
• Migration
o The leukocyte follows chemokine CXCL8
(IL8). To migrate to the site of infection
Cytokines: small proteins released by various cells. Similar to
hormones and can act in intracrine, autocrine, juxtracrine,
paracrine, endocrine and exocrine manner
Types
• Interleukins (IL): cytokines produced by leukocytes
• Myokines: cytokines produced by muscle cells
• Adipokines: cytokines produced by fat cells (most active
cells that produce cytokines – more than T cells)
• Chemokines are chemoattractant cytokines
Know important ones that are secreted by activated macrophages
IFNa/b/lambda
• Direct anti-microbial activity
IL15
• Direct anti-microbial activity
IL1b (endocrine)
• Local effects
o Activates vascular endothelium.
o Activates lymphocytes.
o Local tissue destruction.
o Increase access of effector cells
• Systemic effects
o Fever
o Production of IL6
TNFa (endocrine)
• Local effects
o Activates vascular endothelium and increases
vascular permeability, which leads to increased
entry of IgG, complement, and cells to tissues
and increased fluid drainage to lymph nodes
• Systemic effects
o Fever
o Mobilization of metabolites
o Shock
IL6 (endocrine)
• Local effects
o Lymphocyte activation
o Increased antibody production
• Systemic effects
o Fever
▪ Induces acute phase protein
production
***OKAY, the aforementioned 3 endocrine cytokines (plus IL15)
also have a variety of effects on specific organs and cells, let’s
examine them
LIVER
• Produce acute phase proteins (C-reactive protein,
mannose-binding lectin – both of which bind to residues
on bacterial surfaces, acting as an opsonin and activating
complement)
o Causes activation of complement opsonization
BONE MARROW ENDOTHELIUM
• Neutrophil mobilization (to get to site of infection)
o Phagocytosis
HYPOTHALAMUS
• Increased body temperature
o Decreased viral and bacterial replication
o Increased antigen processing
o Increased specific immune response
FAT/MUSCLE
• Protein and energy mobilization to allow increased body
temperature
o Decreased viral and bacterial replication
o Increased antigen processing
o Increased specific immune response
DENDRITIC CELLS
• TNFa stimulates migration to lymph nodes and
maturation
o Initiation of adaptive immune response
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• CXCL8
o Local effects
▪ Chemotactic factor recruits
neutrophils, basophils, and T cells to
site of infection
• IL12
o Local effects
▪ Activates NK cells and induces the
differentiation of CD4 T cells into
Th1 cells
Local vs. systematic inflammation
Local infection with gram
negative bacteria
Systemic infection with gram
negative bacteria (sepsis) –
cytokine storm
Macrophages activated to
secrete TNFa in the tissue
Macrophages activated in the
liver and spleen secrete TNFa
into the bloodstream
Increased release of plasma
proteins into tissue. Increased
phagocyte and lymphocyte
migration into tissue.
Increased platelet adhesion to
blood vessel wall
Systemic edema causing
decreased blood volume,
hypoproteinemia, and
neutropenia, followed by
neutrophilia. Decreased blood
volume causes collapse of
vessels. (If every single
endothelial cell is activated
and becomes leaky, plasma
starts leaking everywhere,
causing clotting and
hypovolemic shock)
Phagocytosis of bacteria.
Local vessel occlusion.
Plasma and cells drain to
local lymph node
Disseminated intravascular
coagulation leading to
wasting and multiple organ
failure (sepsis example.
overreactive T cells during
cancer therapy. Ebola. Some
SARS cov-2 patients. Too
much cytokine production
and activity is BAD!)
Removal of infection.
Adaptive immunity
Death
ADAPTIVE IMMUNITY OVERVIEW
(intro to APC, MHC, T cells, B cells)
Stages
• Immune recognition
• Immune regulation
• Immune protection
Innate immunity pathogen recognition
• PRRs
o Pattern recognition receptors recognize
common molecular patterns of pathogens
referred to as pathogen associated molecular
patterns (PAMPs)
What are antigens?
• Any molecule that can bind specifically to an antibody
(can be proteins, carbohydrates, nucleic acids).
What are antibodies?
Receptor characteristics
• Innate vs. adaptive
Receptor
characteristic
Innate immunity
(generic)
Adaptive
immunity
(specific)
Specificity
inherited in the
genome
Yes
No
Triggers
immediate
response
Yes
No
Recognizes broad
classes of
pathogens
Yes
No
Interacts with a
range of molecular
structures of a
given type
Yes
No
Encoded in
multiple gene
segments
No
Yes
Requires gene
rearrangements
No
Yes
Clonal distribution
No
Yes
Able to
discriminate
between even
closely related
molecule
structures
No
Yes
TCR:MHC Interaction
• CD4 “helper” T cells (bind to MHC II)
o Extracellular antigen (bacteria)
• CD8 “cytotoxic killer” T cells (bind to MHC I)
o Intracellular antigen (viruses)
Just a note about MHC and where we can find them
Tissue/cell
MHC
Class I
Class II
(found on professional
APCs)
Hematopoietic
T cells
+++
+
B cell
+++
+++
Macrophages
+++
++
Dendritic cells
+++
+++
Neutrophils
+++
-
Erythrocytes
-
-
Non-hematopoietic
///////////////////////////
///////////////////////////
Liver hepatocytes
+
Kidney epithelium
+
Brain
+
Adaptive immunity and pathogen recognition
• TCR and BCR (refer to hand drawn notes)
o Structure
o Function
Generation of diversity
• Germline theory (wrong)
o Separate gene for each different
immunoglobulin
• Somatic diversification theory (correct)
o Recombination of a limited number of gene
sequences (30,000 genes in human genome)
can lead to diversification of receptors
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GENERATION OF DIVERSITY
(T cells and TCRs + B cells and BCRs)
B cells
o BCR structure
• Chains
o 2 heavy chains
▪ 5 main isotypes
• Gamma: IgG
• Mu: IgM
• Delta: IgD
• Alpha: IgA
• Epsilon: IgE
o 2 light chains
▪ 2 isotypes (kappa, lambda)
• Regions
o Variable
o Constant
o Transmembrane
• Surface Ig (aka BCR) vs. antibody
o The surface Ig is bound to the B cell via the
transmembrane region
• Every B cell is clonal, meaning it expresses its own
discrete BCR
T cells
• TCR structure
• Chains
o 1 light chain (alpha chain) has V, J regions
o 1 heavy chain (beta chain) has V, D, J regions
• Regions
o Variable
o Constant
o Transmembrane
• Types
o 2 classes
▪ Alpha beta
▪ Gamma delta
• As opposed to BCRs, TCRs can only recognize
processed antigens that are presented to it in the context
of MHCs
Generation of diversity (there are over 10^12 – a trillion –
different environmental antigens. We only have a limited number
of genes to code for our TCRs and BCRs)
Germline theory (wrong)
• Separate gene for each different immunoglobulin
Somatic diversification theory (correct)***
• Recombination of a limited number of gene sequences
• Applies to both TCRs and BCRs
***Let’s go into detail about somatic diversification
• Variable region genes are constructed from gene
segments
o Light chain rearranges V, J regions
o Heavy chain rearranges V, D, J regions
• 12/23 rule and the recombination signal sequence (RSS)
o Recombination only occurs between gene
segments located on same chromosome
o Only gene segment flanked by a RSS with 12
bp spacer can be joined to one flanked by a 23
bp (so only V and J can go together not V and
V or J and J)
o 12 bp and 23 bp correspond to one and two
turns of the DNA double helix
VDJ recombination continued-
• The process is mediated by VDJ recombinase
o Complex of enzymes consisting of
ubiquitously expressed DNA modifying genes
and RAG-1 and RAG-2 (recombination-
activating genes)
▪ Only expressed in immature
lymphocytes
▪ They loop DNA and bring V and J
regions and cut out intervening
regions
▪ They attach to 12 bp and 23 bp
spacers and cleave off these RSS
motifs
How is there so much diversity though?
• Combinational diversity (the aforementioned VDJ shit)
o Combination of different light (kappa and
lambda) and heavy chains (mu for B cells or
alpha beta and gamma delta for T cells)
• Junctional diversity
o Additional bases may be added by terminal
deoxynucleotidyl transferase (TdT) or
subtracted by exonuclease
o Number of bases added or removed is random
and often disrupt the reading frame
o Frameshift leads to non-functional protein
o DNA rearrangements leading to such
disruptions are known as non-productive
rearrangement (leads to death of that
lymphocyte)
• Somatic Hypermutation (B cells only)
o Introduction of point mutations in the variable
region of the heavy and light chain
o Mechanism underlying affinity maturation
o Otherwise known as the finetuning of the
BCR
B cell development
• Bone marrow
o VDJ recombination
• Periphery (secondary lymphoid organs)
o Somatic hypermutation
T cell development
• Bone marrow
o Born
• Thymus
o Maturation
▪ VDJ recombination
▪ positive and negative selection
ANTIGEN PROCESSING AND PRESENTATION
APCs
• Types of professional APCs
o Dendritic cells
o Macrophages
o B cells
Dendritic cells
• Activation
• Migration
• Presentation
o Endogenous products (MHC I)
o Exogenous (MHC II)
MHC I