Foundations in Immunology Flashcards
Whats a pathogen?
Any microorganism that causes harm
What are physical barriers to pathogens?
Skin
Reproduction, respiratory and digestive tracks
Describe the innate immune system…
Non-specific
First to come into play
Will produce the same response time and again – no memory
Describe the adaptive immune system…
Highly specific
Involves antibody Production
Has immunological memory
Give an example of an innate response.
Splinter enters foot
Area around splinter gets red and swollen
Macrophages flood area
Where Do Macrophages Come From?
Bone Marrow
Monocytes differentiate into them
How to macrophages work?
Mø give off chemicals that restrict blood flow away from site of injury (redness)
Contraction of endothelial cells (swelling)
Produce Cytokines to alert other cells to the ‘danger’ and induce them to travel to the site of injury
What is the main role of the immune system and what does it employ?
Bodies 1st line of defense
Uses physical barriers - tight junctions between epithelum and mucous membranes
Uses phagocytic cells like macrophages and neutrophils
Uses soluble factors
- Growth and Enzyme inhibitors
- Lysins
- Complement proteins
Describe phagocytosis…
Phagocytosis is triggered when the phagocyte recognises a foreign cell.
It is the internalization of foreign matter by cells into cytoplasmic vesicles. Once inside, the matter is digested by lysosomes, which contain enzymes
This also kills the phagocytic cell that did the ingesting.
What are the 3 activation pathways of the complement system?
Classical
Alternative
Lectin
Briefly describe the complement system.
The complement system consists of about 20 individual proteins which act together in an enzyme cascade to form a membrane attack complex
This makes a hole in the pathogen (bacterium) which disrupts the ability of the pathogen to maintain homeostasis and it dies.
What do all 3 pathways always end up with?
C5 convertase
What two pathways are effector mechanisms of the innate immune system?
Alternative and Lectin
What pathway is an effector mechanism of the adaptive immune system?
Classical
What happens with the C5 convertase?
It cleaves C5, which goes on to comine with C6, C7, C8 and C9 to form a MAC.
C5-8 forms the stalk and C9 forms the pore which causes cell cysis - poking hole in the cell.
What does the complement system achieve?
Opsonisation of invaders
C3a and C5a (bits that were cleaved) act as chemoattractants
Functions of the complement system?
Lysis of microbes
Promotes phagocytosis of microbes
Stimulates inflammation - activating mast cells and neutrophils
Also stimulate activation of B Cells and Ab production
What stops NK cells targeting our own cells?
Our cells have MHC class 1 proteins which signal to it that its our cells
Whats a cytokine?
Chemicals used by cells to communicate with other cells
Function of the lymphatic system?
Drainage of tissue
Absorption and transport of fatty acids
Immunity
Differences between lymphatic and blood vessels?
Lymphatic vessels are blind ended cells
Lymph vessels only carry fluid away from tissues unlike blood
What are the 3 phases of immune defence?
Recognition of danger
Production of specific weapons
Transport of weapons to site of attack
Where are blood cells produced and what type of organs are they?
Bone marrow and thymus
Primary lymphoid organs
What is hematopoiesis?
Formation and activation of blood cells
Function of the thymus?
T-cell education
Function of secondary lymphoid organs?
Site of lymphocyte activation by antigens
What 2 areas is the spleen divided into?
Red and white pulp
Function of spleen?
Filtration of blood
What separates red and white pulp?
Marginal zone
What is a high endothelial venule?
Simple columnar cells line venules,
They are slightly looser than normal venules, which allows fluid and lymphocytes to leak out of the blood vessels.
What two zones are lymph nodes separated into?
B and T zones
What effect does B cells have on T cells?
Cause B cells to make antibodies
What are peyers patches?
Patches of smooth cells embedded in villi covered cells
What does MALT stand for and what is it an example of?
Mucosal Associated Lymphoid Tissue - a peyers patch
What covers peyers patches?
M cells
Difference between adaptive and innate immune systems?
Adaptive is very specific and has immunological memory
How does the adaptive immune system display a much larger response to an antigen in repeated exposure?
Presence of memory cells allow a much quicker and stronger response after primary exposure
What are the differences between active and passive immunity?
Active immunity - conferred by a host response to a microbe or a microbial antigen
Passive immunity - conferred by adoptive transfer of antibodies or T lymphocytes specific for the microbe
Active immunity is the only one that generates immunological memory
Why does passive immunity not have memory?
Because it isn’t your own B cells creating the response
Where are B cells made?
Bone marrow
What is the antigen receptor for a B cell
Surface immunoglobulin
Why is it more important to tolerize T cells than B cells?
B cells cannot make antibodies in response to most antigens without the help of T cells
What part of the pathogen are antibodies specific to?
The epitope
What induces B cells to multiply?
Recognition of a specific epitope on a specific antigen on a specific pathogen
What 2 chains are antibodies separated into?
Light and Heavy chain
What modification is made to antibodies after B cells multiply and produce them?
The antibodies will have a much higher affinity for the epitope being targeted
What chain does the antibody bind to?
Light chain
What chain does the cell bind to?
heavy chain
What do the heavy chains define?
The classes of immunoglobulin
What are the classes of antibody?
- IGM
- IGD
- IGA
- IGE
- IGG
Function of IGM?
Fixes compliment and oponization
Function of IGG?
Good opsonizer
Function of IGA
Protects mucosal surfaces, resistant to stomach acid
Function of IGE?
Defends against parasites, cause anaphylactic shock and allergies
What causes antibodies to be flexible?
Presence of a hinge between the light and heavy chains
Why does antigen bound IGM display good complement binding?
Binding to epitope causes a conformational change that allows c1 protein to bind to IgM
What actually is opsonisation?
The process of “tagging” a pathogen which causes fc receptors to “stick up” which causes the pathogen to be more susceptible to phagocytic action
Why is it that mast cells can cause allergic reactions?
When mast cells encounter a pathogen they dump all of their contents onto the pathogen to neutralise it, some of these contents can cause an allergic reaction in the host
What are the different ways to activate a B cell?
T cell dependent and T cell independent complement activation
Describe how T-cell dependent activation works.
Signal from a clustered BCR (a surface IGM) along with a signal from a T cell in which a protein on the surface of a T cell recognises the same antigen as the B cell and then binds to a receptor on the B cell
Where are T cells educated?
Thymus
What is the cell surface receptor in a T cell called
T cell receptor
What conditions have to be met in order for a T cell receptor to recognise antigens?
Has to be bound to a MHC protein
What 2 classes of T cells are there?
Helper CD4+
Cytotoxic CD8+
What types of antigens can T cells recognise?
ANY protein peptide that a pathogen may have due to association with MHC
What is it important for all lymphocytes to learn to do with regard to “self”
Do not recognise the self antigen
What happens to T cells that are unable to interact with MHC molecules or cannot distinguish self from non self
Death by apoptosis
What determines what type of T cell thymocytes develop into?
Whether it binds to MHC 1 (cytotoxic) or MHC 2 (helper)
Purpose of MHC 1?
Presents virally induced peptides to CD8+ T cells and trigger cytotoxic response
Purpose of MHC 2
Presents exogenously produced Ag to CD4+ T cells and activate macrophages and B cells
where is MHC 2 found
On antigen presenting cells
What deciees which T cell a naive T cell turns into after MHC peptide recognition?
A range of different chemicals acting on the T cells
Can helper T cells destroy pathogens?
No
What do cytotoxic T cells release once exposed to infected/dysfunctional somatic cells?
Perforin, which forms pores in the target cell, also releases granzyme B - induces apoptosis
How can T memory cells be formed?
Can arise from fully differentiated cells or from partially differentiated cells.
