Cell recognition and the immune system Flashcards
What is an antigen
Cell surface molecule that triggers/stimulates an immune response
* Usually glyco protein, glyco lipid or polysaccharide
* immune system recognises as self or non self, enabeles identification of cells from other organisms of same species,patheogens, toxins and abnormal body cells
What is a Phagocyte
A macrophage (type of white blood cell) that carries out phagocytosis
found in blood and tissues
What is a Phagocytosis
A non specific response. Any non self cell (e.g patheogen) that is detected will trigger the same response to destroy it
How does Phagocytosis destroy patheogens
- Phagocytes are attracted to chemoattractants from patheogen and move up a concentration gradient towards patheogen via chemotaxsis.
- The phagocyte attaches to the pathogen by binding to its antigens
- Phagocyte changes shape to engulf patheogen (endocytosis), patheogen is trapped within phagocytic vacuole
- once engulfed patheogen is contained in phagosome vesicle
- Lysozymes within phagocyte fuses with phagosome (phagolysosome) and releases its contents (lysozymes)
- Lysozymes causes lysis, hydrolyses patheogen’s cell wall, and digests patheogen
- Phagocyte absorbs soluble products from phagocyte cytoplasm
Give 2 differences between specific and non specific immune responses
nonspecific:(inflammation,phagocytosis)=same for all patheogens (immediate)
Specific: (B and T lymphocytes) complementary patheogen (time lag)
What are T lymphocytes and B lymphocytes
Lymphocytes are white blood cells involved in the specific immune response. All lymphocytes are made in the bone marrow
T cells mature in thymus gland
T cells are involved in cell mediated immunity
B cells mature in bone marrow
B cells are involved in humoral immunity (antibodies in body fluids)
What are Antigen presenting cells (APC)
Any cells that presents a non specific antigen on their surface
- Infected body cells
- macrophage which has engulfed and destroyed a patheogen
- cells of transported organ will have different shaped antigens on their surface compared to your self cell antigen
- cancer cells will have abnormal shaped self antigens
Explain the role of antigen presenting cells (APCs)
Macrophage displays antigen from patheogen on its surface (after hydrolysis in phagocytosis)
enhances recognition by T helper cells which cannot directly interact with patheogens/antigens in body fluid
Name two types of specific immune response
Cell mediated
Humoral
Describe the process of the cell mediated response
- Once pathogen has been engulfed and destroyed antigens are positioned on cell surface (APC)
- Helper T cells have complamentary receptors on their surface which bind to antigens on APC
- Once attactched this activates the helper T cell to divide via mitosis. The clones than differentiate to perform multiple functions
- Activate B lymphocytes to divide
- stimulate macrophages to perform phagocytosis
- Become memory cells
- Activate cytoxic T cells
What do Cytoxic T cells do
Destroy abnormal or infected cells by releasing protein perforin which embeds in the cell surface membrane and makes a pore (hole) so substances can enter or leave cell causing cell’s death
Describe process of the humoral response
(Type B cells have antibodies on their surface)
1. Antigens in blood collide with complementary antibody on a B cell.
2. The B cell takes in antigen by endocytosis and processes and presents it on its cell surface membrane
3. When this B cell collides with T helper receptor it activates the B cell to go through clonal selection via mitosis
4. B cells undergo mitosis to make large number of cells which differentiate into plasms cells or memory cells
Plasma cells produce antibodies complamentry
What do memory B cells do?
Long lived compared to plasma cells. They will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have perviosly encountered.
This results in large numbers of antibodies that can destroy patheogen before any symptoms occur. Active immunity
What are antibodies
Protens secreted by plasma cells
Quaternary structure: 2 light chains held together by disulfied bridges, 2 longer heavy chains
Binding sites on variable region of light chains have specific tertiary structure complementary to a specific antigen making an antigen antibody complex
How do antibodies lead to the destruction of a patheogen
Antibodies are flexible and can bind to multiple antigens to clump them together making it easier for phagocytes to locate and destroy the pathoegens.
Formation of antigen-antibody complexes results in agglutination which enhances phagocytosis
What are monoclonal antibodies what can they be used for
Antibodies are proteins which have binding sites complementary in shape to certain antigens
A monoclonal antibody is a single type of antibody that can be isolated and closed
(Antibodies produced from single clone of B cells)
* Medical treatment
* Medical diagnosis
* pregnancy tests
What is the use of monoclonal antibodies in targeted medication through direct monoclonal antibody therapy
Some cancer can be treated using monoclonal antibodies designed with a binding site complimentary in shape to antigens on outside of cancer cells.
Antibodies are given to cancer patient and attacth to cancer cells. while antibodies are bound to cancer antigens it prevents chemicals binding to cancer cells which enable uncontrolled cell mitosis/division
The monoclonal antibodies prevent the cancer cells growing and as they are designed to only attach to cancer cells they dont harm any other cells
What is the use of monoclonal antibodies in targeted medication through direct monoclonal antibody therapy
Cancer can also be treated with monoclonal antibodies complementary in shape to antigens on outside of cancer cells which have drugs attached to them
This cancer drugs are therefore delivered directly to the cancer cells and kills them reducing harmful side effects traditional chemotherapy and radiotherapy can produce.
‘bullet drugs’
Describe the use of monoclonal antibodies in medical diagnosis
- Pregnancy tests by detecting HCg hormone in urine
- Diagnostic procedures (ELISA TEST)
- Influenza
- Hepatitis
- Chlamdiya
- Prostate cancer
Describe indirect ELISA test
Enzyme linked immunosorbant assay. Used to detect presence of an antibody against a specific antigen.
1. Appy sample to surface e.g test plate to which antigens will attach
2. Antibodies in the sample bind to the antigen was surface to remove excess
3. Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together
4. wash the surface to remove excess antibody
5. Add a secondary antibody with ‘reporter enzyme’ that binds with the first antibody
6. add the colourless substrate of the enzyme, the enzyme act son the substrate to change its colour. Positive result-colour change
What are Viruses
Patheogens that replicate inside of cells making it difficult to destory them without harming host cells.
Antibiotics often work by damaging murein cell walls to cause osmotic lysis, Viruses have no cell wall
Viruses also replicate inside host cells making them difficult to destroy without damaging normal body cells
Describe structure of HIV
Core:Genetic material (2x RNA) and viral enzymes (integrase and reverse transcriptase)
Caspid:Outter protein coat surrounds core
Envelope:extra outer layer made out of membrane taken from the host’s cell membrane
Protein attachments:On the exterior surface of the envelope to enable the virus to attach to host’s helper T cell
*
How does Hiv replicate in helper T cells
- Hiv transported in blood until it binds to complementary CD4 protein receptor on the helper T cells
- The HIV protein then fuses with the helper T cell membrane enabiling the RNA and enzymes to enter
- The HIV enzyme reverse transcriptase copies the vira RNA into a DNA copy and moves to the t helper nucleus (why it is called a retro virus)
- mRNA is transcribed and the helper t cells starts to create viral proteins to make new viral particles
How does HIV cause symptoms of AIDS
HIV positive is when a person is infected with HIV. Aids is when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system
With the T helper cells being destroyed by the virus the host is unable to produce an adequate immune respnse to pathogens and is left vunreable to infections and cancer.
How do Lymphocytes recognise cells
There are 10 million different types of lymphocytes in the body each one can recognise a different shaped antigen. they are made when a foetus in the womb and are unlikely to be exposed to any cells other than self cells
The lymphocytes complementary to the antigens on self cells will dier or production will be supressed to prevent lymphocytes attacking your own cells.
The remaining lymphocytes are complamentary to pathogenic and non self cells
Same process occurs in bone marrow after birth. sometimes lymphocytes will attack own cells causing symptoms of auto immune disease
What is antigen variablity
When a random genetic mutation changes DNA base sequence resulting in different sequence of codons on mRNA . Different primary structure of antigen means that H-bonds ionic bonds and disulfide bridges form in different places in teritary structure
causing diffrent shape of antigen.
Any previous immunity to this patheogen (naturally or artifically through vacc) is no longer effective as all memory cells in the blood will have a memory of the old antigen shape
Ethical issues surrounding the use of monoclonal antibodies
- Involve use of animals (mice to produce antiboidies and tumour cells deliberatley causing cancer)
- Drug trials against athirits and leukaemia resulted in multiple organ failures and deaths
Describe the direct ELSA test
- Monoclonal antibodies bind to bottom of test plate
- antigen molecules in smaple bind to antibody. Rinse excess.
- Mobile antibody with ‘reporter enzyme’ attatched binds to antigens that are ‘fixed’ on the monoclonal antibodies. Rince excess
- add substrate for reporter enzyme positive result-colour change
