Introduction to Immunology Flashcards
What is the main role of the immune system?
It protects your body from harmful substances, germs and cell changes that could make you ill.
It is made up of various organs, cells and proteins.
What are the two branches of the immune system?
Innate immunity
Adaptive immunity
What is innate immunity?
Defense system with which you were born.
It protects you against all antigens.
What are the three components of innate immunity?
- Physical barriers
- Physiological components
- Humoral responses
What are examples of physical barriers of innate immunity?
Skin and mucous membrane
What are examples of physiological barriers of innate immunity?
Acidity of the stomach
Nasal hair
Sweat
What are examples of humoral responses of the adaptive immune system?
Mediated by macromolecules
Secreted antibodies
Component proteins
Antimicrobial peptides
Naturally occurring in the body - found in extracellular fluids
What is adaptive immunity?
Sevelops when a person’s immune system responds to a foreign substance or microorganism, such as after an infection or vaccination.
What are the cells of the innate immune system?
Phagocytes (macrophages and neutrophils)
Dendritic cells
Mast cells
Basophils
Eosinophils
Natural Killer cells
Innate lymphoid cells
What is the role of phagocytes?
Eliminating pathogenic bacteria, fungi and malignant cells, and contribute to adaptive immunity by presenting antigens to lymphocytes.
What is the role of macrophages?
Macrophages are a type of white blood cells, which are active in tissues and are capable of phagocytizing microorganisms.
Macrophages engulf unwanted particles and form a phagosome. This phagosome is fused with a lysosome containing enzymes to digest the phagocytized particle.
What is the role of a neutrophil?
Neutrophils are the most abundant white blood cell type in the blood.
Neutrophils are one of the first cells to migrate into the site of an inflammation, following the cytokine signals produced by the infected cells.
This process of migration is called chemotaxis.
They engulf microorganisms, cell debris as well as dead cells by active phagocytosis.
What is the role of dendritic cells?
Capture, process, and present antigens to adaptive immune cells and mediate their polarization into effector cells
What is the role of mast cells?
Responsible for immediate allergic reactions.
Cause allergic symptoms by releasing mediators.
They release histamine.
What is the role of histamine?
Causes vasodilation, increases permeability of blood vessels, allows fluids rich in proteins to leave the capillary which causes swelling - aids blood clotting.
Vasodilation increases the temperature causing the metabolic rate of the cell to increase so therefore healing rate increases.
Lymphocytes and phagocytes can now easily access the damaged area through the permeable blood vessels.
What is the role of basophils?
Release histamine and heparin
Basophils release them to assist immune system response to destroying the forgein organism
What is the role of heparin?
Prevents blood from clotting too quickly
What is the role of esosinophils?
Help combat parasites
What is the role of natural killer cells?
Effector lymphocytes of the innate immune system that control tumour and microbial infections by limiting their spread and subsequent tissue damage.
NK cells secrete a high level of cytokines which help mediate their function.
What is the role of innate lymphoid cells?
Counterparts of T cells that secret effector cytokines and regulating the functions of other iimmune cells.
What is phagocytosis?
The recognition and ingestion ingestion of bacteria into a plasma membrane derived vescile known as a phagosome.
Is phagocytosis part of the innate or adaptive immune system?
Innate
Why is phagocytosis imporant?
Phagocytosis is also important for the elimination of apoptotic cells and hence fundamental for tissue homeostasis.
What cells are involved in phagocytosis?
Neutrophils
Macrophages
Dendritic cells
B lymphocytes
What are the steps of phagocytosis?
- Virus and cell need to come into contact with each other
- Virus binds to the cell surface receptors on the macrophage
- The macrophage starts to surround the virus and engluf it into the cell
- The surrouded virus becomes completely enclosed in a bubble-like structure called a phagosome within the cytoplasm
- Phagosome fuses with a lysosome, becoming a phagolysosome
- Phagolysosome lowers the pH to break down its contents
- Once contents have been neutralised, the phagolysosome forms a residual body that contains the waste products from the phagolysosome.
What are other mechanisms that can be used to destroy pathogens inside the phagolysosome?
Oxygen radicals
Nitiric oxide
Antimicorbial proteins
Antimicrobial peptides
Binding proteins
What is the role of cytokines?
Peptides released by a range of cells inclusing macrophages, T lymphocytes and mast cells.
They regulate the maturation, growth and responsibeness of particular cell populations.
Cyrokines are important in host immune responses ot infection, inflammation, trauma, sepsis and cancer.
What are lymphoid organs?
Organs of the lymphatic system
What are the primary lymphoid organs?
Primary lymphatic organs are where lymphocytes are formed and mature. They provide an environment for stem cells to divide and mature into B- and T- cells.
Exmaples include: the bone marrow and thymus gland
What are the secondary lymphoid organs?
It is in these organs where the cells of the immune system do their actual job of fighting off germs and foreign substances.
Examples include: lymph nodes, the spleen, the tonsils and certain tissue in various mucous membrane layers in the body
What are the cells of the adaptive immune system?
B cells
T cells
What are B cells?
A type of lymphocyte that produce antibodies to fight bacteria and viruses.
What is the structure of antibodies?
The antibodies produced by B cells are Y-shaped proteins that are specific to each pathogen and are able to lock onto the surface of an invading cell and mark them for destruction by other immune cells.
What is another word for antibody?
Immunoglobulin
What is the role of antibodies?
- Antibodies are secreted into the blood and mucosa, where they bind to and inactivate foreign substances such as pathogens and toxins (neutralization).
- Antibodies activate the complement system to destroy bacterial cells by lysis (punching holes in the cell wall).
What are the types of T cells that are important to note?
T-helper 1
T-helper 2
Cytotoxic T cells (Tc)
What is the function of T helper cells?
They help activate B cells to secrete antibodies and macrophages to destroy ingested microbes.
They also help activate cytotoxic T cells to kill infected target cells.
Why are T helper cells one of the most important cells in adaptive immune system?
They are needed for almost all adaptive immune system responses
What is the role of T-helper 1 cells?
Stimulate B cells to produce antibodies
AKA CD4+
What is the role of T-helper 2 cells?
T helper 2 (TH2) cells orchestrate protective type 2 immune responses, such as those that target helminths and facilitate tissue repair, but also contribute to chronic inflammatory diseases, such as asthma and allergy.
aka CD8+
What are T cells taught during maturation in the thymus?
They are taught to recognise own MHC - those that identify it as yours are allowed to live and move on to the next test, after that the T cell isn’t allowed to recognise MHC plus own peptide
When do T cells mature into CD4+ and CD8+ cells?
After they have been taught to recogconise the MHC
What is the function of cytotoxic T cells (Tc)?
They destroy cells infected with viruses.
Another name for cytotoxic T-cells is killer T-cells
Define major histocompatibility antibody (MHC)
The function of MHC molecules is to bind peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T cells.
What is the complement?
Complement is a system of plasma proteins that can be activated directly by pathogens or indirectly by pathogen-bound antibody, leading to a cascade of reactions that occurs on the surface of pathogens and generates active components with various effector functions.
What is antigen processing?
Antigen processing, or the cytosolic pathway, is an immunological process that prepares antigens for presentation to special cells of the immune system called T lymphocytes.
Define active immunity
Active immunity is defined as immunity to a pathogen that occurs following exposure to all or part of that pathogen.
Direct infection or vaccine, happens overtime, long term to life long, generates memory cells
Define passive immunity
Intouduced from outside of the body
Mother to baby transfer, breast milk, theraputic injection
Takes effect immediately, short term and does not generate memory cells
What are memory cells?
Lymphocytes are produced in response to the specific antigens on a pathogen. After the pathogen is removed some of the lymphocytes continue to remain in the immune system. These are called memory cells.
What is the receptor on a T cell called?
T cell receptor
Recognises antibody when bound to MHC
When will a T cell recognise the antibody?
When ound to MHC
When do T cells mature into CD4+ and CD8+ cells?
After they have been taught to recognise MHC
Where can you find MHC class 1 proteins?
Virtually all nucleated cells
What is the function of the MHC class 1 molecule?
Presents antigenic peptide, Showi the CD 8+ T cell what is being produced in the cell, triggers a cytotoxic response - releases perforin, releases granzyme B, a protese that enters the cell through the pore and causes apoptosis
Where can you find MHC class 2 proteins?
In antigen presenting cells, such as B cells, macrophages and dendritic cells.
What is the function of MHC class 2 receptors?
Presents antigenic peptides to CD4 helper T cells which activates macrophages and B cells
Why are T cells said to have memory?
They are capable of remembering what has activated them once.
Meaning on second exposure they can activate faster and stronger.
How is lymph fluid formed?
Lymph is the fluid that is formed when the interstitial fluid containing dissolved components of the blood enters the conduits of the lymphatic system.
How is the lymph pumped through the body?
Contractions of skeletal muscles
Where do lymphatic vessels carry their fluid?
Away from tissues
What is the name given to the smallest lymphatic vessel?
Lymphatic capillaries
Why can’t fluid escape lymphatic vessels but it can enter?
The walls are composed of endothelium in which simple squamous cells overlap to from one-way valves
Where do both lymphatic trunks drain their fluid?
The blood circulatory system at the right and left subclavian vein
Which part of the bone marrow can be considered lymphatic tissue?
The stem cells in the marrow from which lymphocytes develop, but not in the red bone marrow because there is no lymphatic tissue in the myeloid tissue (tissue which is able to form hematopoeisis
What is a thymocyte?
A T cell precursor
What is the epitone?
The part of the antigen that can be recognised
What do B cells mature into?
What do B cells mature into?
What is the antigen receptor for the B cell?
Surface Immunoglobulin
What type of bond exists in the antigen binding region?
Disulphide bond
What is the epitope of an antigen?
The part of an antigen molecule to which an antibody attaches itself
What is the fab region of an antibody?
The part of the antibody which is responsible for binding to the antigen. The V shaped part of a letter Y
What is the lower region of an antibody called?
Fc region
Where is the light chain portion of the antibody?
Inner lining of the V shape
Where is the heavy chain portion of the antibody?
Surrounds the outside of the shape apart from where the light chain lies
What is the variable region of an antibody?
The upper part of the strands on the Y shape
Does light chain affect the immunoglobulin (antigen receptor surface of antibody)?
No
Does changing the heavy chain affect the immunoglobulin?
Yes, they define the class of Ig
Describe the meaning of the constant region of an antibody
Defines the class of antibody - so the same in every antibody of the same class
What is the variable region of the antibody?
The part that differs between B cells, allowing antobodies collectively to bind to loads of different things
How many types of heavy chain exist?
5
What are the 5 different types of antibodies and their functions?
IgM - good at fixing compliment and opsonisation
IgG- Good at opsonising
IgA - protects mucosal surfaces, resistant to stomach acid
IgE - Defends against parasites - responsible for anaphylactic shock
IgD - No known Ab function
What is T cell dependant activation of a b cell?
T cell surface protein recognises the same antigen as the B cell - Signal is given by a newly formed cluster of b cell receptors, signal also given off by T cell
When will independent activation of a B cell occur?
When a huge number or b cell receptors are clustered together by an antigen with a very large number of repeated epitopes
What is the first antibody to be produced by an antibody?
IgM
What influences the type of antibody the B cell produces as it matures?
The chemicals surrounding the area of infection
How are antibodies able to bind to epitopes far apart on the antigen.
They are flexible
Where can IgA be found?
In the gut
How many antigens is each BCR specific to?
1
What must happen to the BCRs before a signal is sent?
They have to cluster together
Why is independent activation of B cells important?
T cells only recognise proteins, not all antigens are proteins
