topic 2C: cells and the immune system Flashcards
antigen definition
antigens are foreign, specific molecules (proteins, glycoprotien or glycolipid) found on the surface of all cells, where these molecules are recognised as foreign by the immune system, they stimulate an immune response leading to the production of antibodies
how are cells identified by the immune system?
each type of cell has specific molecules on its surface (cell surface membrane/ cell wall), which are often proteins that have a specific tertiary structure, or glycoproteins/ glycolipids
what types of cells and molecules can the immune system identify?
-pathogens (organisms causing disease) e.g. bacteria, viruses, fungi - all pathogens have a specific antigen on their surface, identified as foreign by immune system cells, which then respond to destroy the pathogen
-cells from other organisms of the same species (e.g. organ transplant, blood transfusion) - cells have antigens different to your own triggering an immune response leading to rejection of transplanted organs
-abnormal body cells e.g. tumour cells or cancer/ virus-infected cells - abnormal antigens on surface, triggers immune response
-toxins (poisonous molecules) - produced by bacteria, immune system respond to toxins as well as the pathogens that release them
antigenic variation
-some pathogens have many different strains and antigens on the surface of each strain are different, as they change frequently due to genetic mutations
-the DNA in a PATHOGEN may MUTATE frequently - if a mutation occurs in a gene that leads to a difference sequence of DNA, that codes for the antigen (protein)
-a DIFFERENT SEQUENCE OF AMINO ACIDS is coded for, which changes the PRIMARY STRUCTURE of the antigen (protein)
-this alters the TERTIARY STRUCTURE of the antigen (protein) as bonds form in different places - causing it to change, resulting antigens having different 3D shapes
-as the antigens are a new shape, the previous natural immunity to this pathogen is no longer effective, as memory cells are specific to only one type of antigen
antigenic variability in a vaccine
-the antigens on pathogens may MUTATE frequently and change shape due to gene mutations, so that it’s ANTIGENS CHANGE SUDDENLY rather than gradually this creates new strains
-this means vaccines suddenly become INEFFECTIVE because the new antigens on the pathogen are no long recognised by the immune system
-therefore the B MEMORY CELL receptors cannot bind to the new antigen on the secondary exposure
-therefore the immune system does not produce antibodies (the specific antibodies are not complementary and cant bind to new antigen) and to destroy the pathogen
pathogens definition, example + cause of disease
- a microorganism that causes disease e.g. bacteria, viruses and fungi
-damaging host cells and releasing toxins
describe the two different parts of the immune system
NON SPECIFIC immune response: phagocytosis and physical barriers (skin, mucus)
SPECIFIC immune response: T and B lymphocytes - cellular and humoral response
phagocyte
a phagocyte (e.g. macrophage) is a type of white blood cell that carries out phagocytosis (engulfment of pathogens). They are found in the blood and in tissues and the first cells to respond to an immune system trigger inside the body - they carry out a non specific immune response.
- describe phagocytosis of pathogens + antigen presenting cells
-the phagocyte (e.g. macrophage) recognises and binds to the foreign antigens on a pathogen
-the phagocyte ENGULFS the pathogen by surrounding it with its cell membrane
-the pathogen is contained within a PHAGOSOME VESICLE in the cytoplasm of the phagocyte
-a lysosome (contains enzymes called lyzozomes) fuses with the phagosome vesicle and releases lyzozymes (hydrolytic enzymes)
-the lyzozymes hydrolyse the pathogen
-phagocytosis leads to presentation of antigens where antigens are displayed on the phagocytes CELL SURFACE MEMBRANE, stimulating and activating the SPECIFIC immune response - either cellular and humoral response
lymphocytes
-lymphocyte are another type of white blood cell
-important role in the specific immune response: slower in action at first, but they can provide long term immunity
-produced in the bone marrow by stem cells
TWO TYPES OF LYMPHOCYTES
-T-lymphocytes (T cells) - involved in cellular response
-B-lymphocytes (B cells) - involved in humoral response
- describe the response of T lymphocytes (T-cells) to a foreign antigen (cellular response) + types of different cells produced
-a specific HELPER T-CELLS have a complementary receptor protein on the cell surface which binds to an antigen on an antigen presenting cell
-this ACTIVATES the helper t-cell to divided rapidly by mitosis to replicate and form clones
-the cloned helper t-cells differentiate into different cells:
-remain as helper t-cells and activates B-LYMPHOCYTES which secrete antibodies and carry out humoral response
-stimulate PHAGOCYTES (macrophages) to perform more phagocytosis (engulf pathogens)
-produce CYTOTOXIC CELLS which destroys abnormal (tumour) or destroys virus infected cells by releasing perforin
- describe the response of B lymphocytes to a foreign antigen (the humoral response) + what is clonal selection? UPTO MOCK
CLONAL SELECTION
-a specific B lymphocyte with a complementary receptor (antibody on cell surface membrane) binds to an antigen
-The B cell is ACTIVATED by the cytokines released by a specific helper T-cell
-the B cell divides rapidly by mitosis to form clones which differentiate into:
-B plasma cells: secretes large amounts of (monoclonal) antibodies
-B memory cells: remain in the blood and divide to produce plasma cells which produce more antibodies more rapidly for the secondary exposure if the same antigen and secondary immune response
- role of B plasma cells + B memory cells UPTO MOCK
B PLASMA CELLS (slower + short lived - primary immune response)
-plasma cells produces and secretes large amounts of monoclonal antibodies, which are specific to the antigen
B MEMORY CELLS (faster + long lasting - secondary immune response)
-remain in the body (blood) for secondary immune response
-memory B cells divide by mitosis and produces plasma cells which release more antibodies more rapidly after the second exposure to the same antigen
antibody definition
-antibodies are quaternary structure PROTEINS (4 polypeptide chains), secreted by B lymphocytes (e.g. plasma cells in response to specific antigens), they bind specifically to antigens forming antigen-antibody complexes
antibody structure
-Quaternary structure proteins (4 polypeptide chains)
-the specificity of an antibody depends on its VARIABLE REGIONS, which form the antigen binding sites
-each antibody has a VARIABLE REGION with a unique tertiary structure (due to different sequence of amino acids) that’s complementary to one specific antigen
-all antibodies have the same CONSTANT REGION (doesn’t change)
-2 SHORT (light) CHAINS + 2 LONG (heavy) CHAINS
explain how antibodies lead to the destruction of pathogens
-(monoclonal) antibodies bind to the antigens on the surface of the pathogen to form lots of ANTIGEN-ANTIBODY COMPLEXES (antibodies have a specific tertiary structure so binding site binds to the complementary antigen)
-an antibody has TWO BINDING SITES so can bind to TWO PATHOGENS at a time causing AGGLUTINATION, which is where pathogens become clumped together
-antibodies attract phagocytes, so phagocytes bind to the antibodies and phagocytose (engulfs) many pathogens at once
-this process leads to the DESTRUCTION of pathogens carrying this antigen in the body
primary response (initial response to first exposure)
-occurs when a foreign antigen enter the body for the first time it activates the immune system, this is the primary response
-primary response is a SLOW (so antibodies are produced slowly and at a lower concentration) because there aren’t many B-cells and takes time for specific B plasma cells to activate and produce the specific antibody needed to bind to the antigen
-eventually the body will produce enough of the right antibody to overcome the infection, meanwhile the infected person will show SYMPTOMS of the disease
-MEMORY cells are produced by T and B cells -they remember the specific antibodies needed to bind the antigen
-person is now immune - immune system has the ability to respond quickly to a second infection
secondary response (secondary response to second exposure to antigen)
-if the same pathogen enters the body again, the immune system will produce a FASTER, stronger response, this is the secondary response
-CLONAL SELECTION happens FASTER (so antibodies are produced faster and at a higher concentration): MEMORY B-CELLS are activated and divided rapidly by mitosis into plasma cells that produce MORE SPECIFIC ANTIBODIES MORE RAPIDLY to the specific antigen + MEMORY T-CELLS are activated and divided into the correct type of T-cells to kill the cell carrying the antigen
-the secondary response is quick so often destroys the pathogen before show any symptoms (immune to the pathogen)
vaccine definition
-an injection of antigens from a dead pathogen, stimulating the production of memory cells
explain how vaccines provide protection to individuals against disease
- a specific B-LYMPHOCYTE with
complementary receptor binds to ANTIGEN - a specific HELPER T-CELL binds to an ANTIGEN-PRESENTING CELL (antigen on surface of phagocyte) and STIMULATES the B-cell to go through CLONAL SELECTION: clonal expansion and differentiation
- B lymphocyte divides by MITOSIS to form clones
- Some differentiate into PLASMA B-CELLS which secrete ANTIBODIES complementary to the pathogens antigen + some differentiate into MEMORY B-CELLS which remain in the blood (primary response)
- On SECONDARY EXPOSURE to antigen, memory B-cells rapidly divide by mitosis to produce plasma B-cells in large quantities
- These antibodies FASTER and at a higher concentration
- so the specific antibody can bind to the specific antigens, causing agglutination (clumping of pathogens together) which will encourage phagocytosis of the pathogen and destroy it
- this happens rapidly to prevent experiencing symptoms (secondary response)
herd immunity definition
a large proportion of population vaccinated against a specific pathogen, this is reducing the spread of the pathogen
Explain how vaccines provide protections for populations against disease
-a large proportion of population are immune so do not become ill or get symptoms from the infection
-fewer infected people to pass the pathogen on / unvaccinated people less likely to come in contact with someone with disease
active immunity
-immunity created by your immune system makes its own antibodies after initial exposure to an ANTIGEN and antibodies and memory cells are produced.
-natural: body creates its own ANTIBODIES produced and secreted by PLASMA B-CELLS and creates MEMORY CELLS
-artificial: VACCINATION (containing a harmless dose of antigen)
-SLOW acting, takes longer to develop protection, however LONG TERM IMMUNITY as antibody can be produced in response to a specific complementary antigen being present in the body again
passive immunity
-this is the type of immunity you get from your body being introduced to ANTIBODIES made by a different organism - your immune system doesn’t produce any antibodies of its own. there is NO EXPOSURE to antigen, so plasma cells and memory cells are not made
NATURAL: e.g. a baby becomes immune due to the antibodies it receives from its mother through the placenta and in breast milk
ARTIFICIAL: immune after being injected with antibodies from someone else e.g. blood donations
-protection is FASTER acting but SHORT TERM IMMUNITY as antibody HYDROLYSED + no memory cells are created - as no exposure to antigen
