Module 5: Immunology Flashcards
Three components of the immune system
Organs
Cells
Molecules
Immune system
Organised system of organs cells and molecules that interact together to defend the body against disease
What kind of diseases can the immune system affect? (3)
Infectious
Inflammatory
Cancer
Primary lymphoid organs (2)
Thymus
Bone marrow
(Produce white blood cells/ lymphocytes)
Secondary lymphoid organs (3)
Tonsils
Spleen
Lymph nodes
Sites where immune responses are initiated
What occurs in the bone marrow?
Stem cells are sourced
They develop into cells of the innate and adaptive immune responses
What occurs in the thymus?
Developing T cells learn not to react to self (school)
What occurs in the spleen?
Initiation of immune responses against blood-borne pathogens
What occurs in the lymph nodes? (2)
Lymph fluid is filtered from blood and tissue
Immune responses are initiated
Three layers of defence of the immune system
Chemical and physical barriers
Innate arm
Adaptive arm
Which is slower to take action- innate or adaptive arm?
Adaptive
Physical barrier for the immune system
Skin
Two layers of the skin, what do they contain?
Epidermis- dead cells, keratin and phagocytic immune cells
Dermis- thick layer of connective tissue, collagen, blood vessels and phagocytic immune cells
What do phagocytic immune cells do?
Engulf and kill microbes
Dendritic cells
Immune cells in the skin
Have dendritic arms that give big surface area which is good for communication between innate and adaptive arms
Chemical defenses of the skin (4)
Antimicrobial peptides (e.g. defending which form pores in microbial cell membranes)
Lysozyme- breaks down bacterial cell walls
Sebum- low pH so microbes can’t grow
Salt- hypertonic dries out microbes
Where are sebum and salt secreted?
Sebaceous gland and sweat gland
Where are mucous membranes present? (4)
Inner body parts that come into contact with the air
Eyes
Respiratory tract
GI tract
Genital/rectal tract
Three components of mucous membranes
Mucus layer
Epithelium
Fibrous connective tissue (lamina propria)
Where are goblet cells, and what do they produce?
Epithelium
Mucus
Direction and function of mucociliary escalator
Up to pharynx
Cilia move dust and trapped microbes up to be swallowed- which get destroyed in the gut
What other cells accompany goblet cells in the epithelium?
Columnar cells
Chemical defences of mucosal surfaces (6)
Stomach- low pH (breaks down microbes)
Gall bladder- bile (antimicrobial)
Intestine- digestive enzymes (break down microbes)
Mucus (transports microbes away)
Defensins (antimicrobial peptides)
Lyzozyme- tears, urine (break down cell walls)
Which has more cell layers- skin or mucous membranes?
Skin
Which contains alive cells- mucous membranes or skin?
Both
Skin also contains dead cells in outer layers
Why is sebum present in the skin, but not in mucous membranes?
Because there are hairs on the skin to which it’s attached
In which tubes are cilia present on mucous membranes?
Trachea and uterine tubes
How do innate and adaptive arms communicate?
Through dendritic cells
Innate internal defenses (5)
Phagocytes Natural killer cells (kill virus-infected cells) Inflammation Antimicrobial proteins Fever
Two cells of the adaptive defense and their functions
B cells- make antibodies
T cells- produce chemical messengers and become killer cells
Which arm of the immune system can discriminate between viruses, and even strains of a virus?
Adaptive arm
Which has a long-term specific memory: adaptive or innate arm?
Adaptive (innate has no specific memory)
What can the innate arm detect if it can’t discriminate between viruses?
Molecular components
- cell wall components
- nucleic acids
Etc.
Two general components of blood
Plasma (55%)
Cells (45%)
What does plasma include?
Proteins
Water
Other solutes
Which three cells make up the 45% formed elements in the blood?
Platelets
White blood cells
Red blood cells
Name for white blood cells
Leukocytes
Where are blood cells sourced, and what is this process called?
From the bone marrow
Hematopoiesis
Hematopoietic cells
What three lineages derive from them?
Stem cells that develop into blood cells
Erythropoietin
Myeloid
Lymphoid
Erythroid lineage
Red blood cells (erythrocytes) derived from hematopoietic stem cells
Four innate immune cells
Which lineage are these?
Granulocytes, monocytes, dendritic cells, platelets
Myeloid lineage
Derived from hematopoietic stem cells
Adaptive immune cells
What lineage do they come from?
B and T lymphocytes
Lymphoid lineage
Which two lineages are white blood cells?
Myeloid and lymphoid
Granulocyte in blood
Neutrophil
Neutrophils
Granulocyte in the blood which makes up 75% of all leukocytes
Highly phagocytic
Granulocyte in tissue
Mast cells
Where are mast cells found?
Lining mucosal surfaces
How do mast cells attract white blood cells to areas of tissue damage?
By releasing granules which acts as a signal
Two types of phagocytic cells
Where are they present?
Monocytes- blood- low phagocytosis
Macrophages- tissues- high phagocytosis
How are monocytes related to macrophages?
Monocytes develop into macrophages when they leave the blood
Macrophages can be sessile or migratory- what does this mean?
They can become resident or move through tissues
Three functions of macrophages
Phagocytosis
Release of chemical messengers
Show information about pathogenic microbes to T cells (linking arms)
Which is the most important cell to help trigger adaptive immune responses?
Dendritic cells
How do cells of the immune system move around the body?
Leave blood to enter tissues
Carried in the lymph which is drained into lymph nodes
PAMPS
Pathogen-associated molecular patterns
Three components to a virus PAMP
Nucleic acid (ssRNA or dsRNA)
Nucleocapsid (protein)
Envelope (sometimes)
Five components of a bacterium PAMP
Nucleic acid Cell membrane Cell wall Capsule (sometimes) Flagella
Building blocks of flagella
Flagellin
What kind of nucleic acid is commonly present in bacteria?
Unmethylated CpG DNA
Common building blocks of bacterial cell wall (3)
LPS (lipopolysaccharide)
Endotoxins
Lipoteichoic acid
How does a phagocytic cell recognise microbes?
Through its PRRs (pattern recognition receptors)
What components of microbes do PRRs recognise?
Bacterial cell wall components
Yeast cell wall components
What do PRRs do once they recognise components of a microbe?
Send a signal to the phagocytic cell nucleus to regulate gene transcription
Makes lots of proteins to fight specific microbe
Pyrexia
Fever
What is released by immune cells during fever?
Pyrogens
IL-1
Interleukin-1
Produced by phagocytes after ingesting bacteria
Why is fever useful?
Decreases phagocytosis
Which decreases IL-1
Which decreases temperature
When do numbers of neutrophils in blood increase? Why?
During infection
Granulocytes circulate in the blood and move into tissue during inflammation
How do dendritic cells link the innate and adaptive?
Drain into lymphatic vessels to lymph nodes
Where they activate T and B cells
B cells produce _____
Antibodies
Antibodies do: (2)
Label bacteria for phagocytosis
Block interaction between bacterial cell and receptor
What do cytotoxic T cells do?
Send death signals
Where are dendritic cells present?
In major organs
Mostly in skin
What do dendritic cells do when they come across an antigen?
Phagocytose it and process it down to peptides- then present it on MHC to T cells
If dendritic cells are in the blood, where do they migrate to after phagocytosing an antigen?
The spleen
Antigen
Anything that has the potential to be recognised by the immune system
Auto-antigen
Self-antigen
Protein made by our own cells (usually immune system is tolerant of these)
APC (3)
Antigen presenting cell- any cell that can present antigens to T cells
- macrophages
- dendritic cells
- B cells
Two types of T cells
CD8
CD4
What does CD4 do? (2)
Helps CD8
Activates B cells
What do B cells do once activated?
Differentiate into plasma cells
What do plasma cells do? Where are they found?
Make lots of antibodies
Lymph nodes and spleen
What does CD8 become when presented with an antigen?
CTL (killer cell) which kills virus-infected cells
How do CTL cells kill virus infected cells?
Sending killer signal (peforin/ granzyme)
MHC
Major histocompatibility complex (I and II)
TCR
T cell receptor
Where on the APC and T cell is the antigen presented?
On the MHC
Which MHC do CD8 cells recognise?
MHC-1
MHC-II is recognised by which T-cell?
CD4
What about their immune systems separate vertebrates and invertebrates?
Invertebrates only have innate immunity
Endogenous antigen
An antigen which lives inside the cell (eg virus)
Exogenous antigen
An antigen which enters the cell when its phagocytosed
Which cells express MHC-I? Why?
MHC-I presents endogenous antigens
All unnucleated cells have MHC-I
Which cells express MHC-II as well as MHC-I? Why?
Antigen-presenting cells (APC) because MHC-II presents exogenous antigen
Describe MHC-I antigen processing (3)
Antigen proteins are degraded to peptides in cytoplasm
Peptides are imported into ER
In the ER, peptides are loaded on MHC-I
Describe MC-II antigen processing (3)
Antigen proteins are degraded in an acidic phagolysosome
Peptides are loaded on MHC-II in phagolysosome
MCH-11 and peptide travel to cell membrane
T cells proliferate when activated by APCs. What does this mean?
They make more of themselves
Two examples of endogenous antigens
Viral proteins produced during viral replication
Proteins produced by intracellular bacteria
Examples of exogenous antigens (3)
Fungi
Bacteria
Parasites
What property of a phagolysosome breaks down exogenous antigens?
It’s acidity
What three things occur in the thymus?
Creates a pool of T cells that can recognise antigens
Gets rid of T cells that recognise self antigens
TCR gene rearrangement
What is the purpose of TCR gene rearrangement?
Each T cell has a TCR specific for one antigen
Naive T cell
A T cell that has undergone TCR gene rearrangement, but hasn’t carried out immune response
Thymocyte
Immature T cell - hasn’t undergone TCR gene rearrangement
Coreceptors on CD4 and CD8 cells
Function
CD4 and CD8
Stabilises interaction between MHC/peptide and TCR
Which T cell makes cytokines? What do these do?
CD4
Cytokines are soluble messengers which support other immune cells
Other name for CD4 cells
Helper T cells
Which T cell makes cytotoxic molecules?
CD8
Name two cytotoxic molecules
Perforin
Granzyme
What do cytotoxic molecules do?
Kill infected cells
What cell can CD8 cells develop into once activated?
Cytotoxic T lymphocytes (CTL)
Effector T cells and their functions (4)
Activated T cells
Kill infected cells
Make cytokines
Support antibody production
Remember the antigen for next time
How does a CTL know which cells to kill?
They will express the peptide on MHC-1 on their cell surface that the CTL has the TCR for
Memory T cells
CD4 or CD8 cells that reside in the body for long periods of time
They have been activated before, and can be activated much quicker than naive cells
Which concept/ science is based on the function of memory cells?
Vaccination
HIV infection leads to loss of ______
CD4 T cells
Which cells does CD4 help to activate?
CD8 and B cells
Where are B cells made?
Bone marrow
BCR
B cell receptor
Two parts of antibody
Heavy chains and light chains
An antibody is a secreted ____
BCR
What is different about the way T cells and B cells recognise antigens?
B cells don’t need MHC to recognise it
Functions of antibody (3)
NOC
Neutralisation
Opsonisation
Complement activation
Describe viral neutralisation
Antibodies coat virus so it can’t attach to receptor on host cell
This neutralises virus activity
What is the name of the process that makes bacteria tastier for macrophages?
Opsonisation (antibodies bind)
Describe complement activation
Antibodies bind to host cell
Complement proteins can bind to the antibodies
It activates complement pathway to destroy pathogen more quickly
Five antibody isotypes
IgM IgG IgA IgE IgR
Describe IgM and it’s function
Pentamer antibody with J chain
First Ig class produced after initial exposure to antigen
Expressed on naive B cells and acts as BCR
Very effective in activating complement
Targets extra cellular bacteria
Describe IgG and it’s function
Monomer antibody
Most abundant Ig class in blood
Opsonises/ neutralises
Only Ig class that can cross the placenta
Targets virus and bacteria
Passive immunity
Acquired immunity of fetus from mother through placenta
Describe IgA and it’s function
Dimer antibody with secretory component and J chain. Exists in monomeric form in blood (more stable as dimer in secretory areas)
Present in secretions incl breast milk
Defends mucosal membranes
Targets virus and bacteria
Describe IgE and it’s function
Monomer antibody
Present in blood at low concentrations
Activates mast cells by binding them to parasites
Causes allergic reactions
IgD and it’s function
Monomer antibody
Expressed on naive B cells
Function unknown but can act as BCR
What happens to the B cells that are stimulated, but don’t differentiate into plasma cells?
They form a pool of memory cells
Where are memory cells found?
In blood and lymph
Do memory B cells secrete antibody?
No, but they express it as BCR
What happens if a memory B cell sees the same antigen for a second time?
Becomes plasma cells and secretes antibody
Primary immune response
Involves naive B cells
Takes 7-14 days to produce sufficient antibody to eliminate pathogen
Mainly IgM
Secondary immune response
Relies on memory B cells
Takes 2-3 days to produce sufficient antibody to eliminate pathogen
Mainly IgG
Higher amounts of antibodies produced
