Immune System Flashcards
Antigen
Protein that triggers immune response if identified as non-self
Cell-surface protein which enables cell recognition and identification of cells of different organisms, pathogens, toxins and abnormal cells
Antigen Variability
When the antigen on pathogens is altered frequently
Secondary immune response is prevented as it is specific.
Memory cells and antibodies are no longer complementary to antigen and can not bind.
Therefore the host suffers disease again
Specific vs Non Specific Immunity
Nonspecific is the same for all pathogens whilst specific is complementary to specific pathogens.
Nonspecific is immediate whilst specific has a time lag.
Specific is longer lasting .
Phagocytosis
Phagocyte moves towards pathogen via chemotaxis (moves along concentration of chemotactic agent)
Pathogen binds to the chemicals on the surface of the pathogen
Phagocyte engulf pathogen to from a phagosome (invagination of plasma membrane)
Lysosomes bind to pathogen to form phagolysosome and release lysozymes into phagosome.
Lysozymes hydrolyse pathogens and the products are absorbed by phagocyte
Phagocytes may present some of the pathogens antigens absorbed on their surface
Antigen Presenting Cells
The antigens of the pathogen are presented on the surfaces of cells e.g. phagocytes, forming APCs e.g. macrophage.
These enhance the recognition of the antigens by helper T cells which can not interact with actual pathogens
B vs T lymphocytes
Both made in bone marrow
B: mature in bone marrow
T: mature in the thymus
B: acts in body fluids
T: acts on body cells
Cell Mediated Response
Receptors on specific helper T-cells bind to antigens on APCs (e.g. macrophages)
Activates the T-cells to divide rapidly via mitosis into a clone of genetically identical cells
Cloned T-cells: develop into memory cells, stimulate phagocytosis, activate cytotoxic T-cells
Cytotoxic T-cells secrete enzyme called perforin which kills infected cells by making the cell surface membrane permeable to all substances
Humoral Response
Receptors on specific helper T-cells bind to antigens on APCs (e.g. macrophages)
Helper T-cell activates complementary B-lymphocytes causing them to rapidly divide via mitosis
These B-cells differentiate into plasma cells which can secrete antibodies that destroy the pathogen and memory B-cells which circulate the blood prepared for a second infection
Antibody (Definition, Structure, Function)
Protein with a quaternary structure that binds to antigens and causes agglutination or acts as a marker for phagocytes
Have two heavy chains (bonded by disulphide bridges) and two light chains.
Has a constant region (do not vary) and a variable region (changes to cause specificity to an antigen)
Has two antigen binding sites (with amino acid sequences specific to an antigen)
Each antibody binds to two antigens at the two antigen binding sites creating antigen-antibody complexes, this causes agglutination where the pathogens are clumped together enhancing phagocytosis.
Vaccines
Dead or weakened form of pathogen which induces primary immune response leading to the creation of memory cells so there is a rapid secondary immune response producing more antibodies in the event of infection by the pathogen.
Active vs Passive Immunity
Active Immunity is when an immune response is triggered creating antibodies within the body
Passive immunity is when an immune response is not triggered and antibodies are created outside of the body
HIV
Retrovirus
Attachment proteins bind to the complementary receptors on helper T-cells
Viral RNA and viral proteins are released into the cell.
The viral RNA is converted into viral DNA via the enzyme reverse transcriptase.
The viral DNA is inserted into the host DNA and is used to make viral proteins which are assembled into new viruses which leave the cell by exocytosis and infect other cells.
Monoclonal Antibodies Uses
Targeted treatment, drugs attached to antibodies so they only target cells with the complementary antigen.
Pregnancy tests
Diagnosis, e.g. ELISA
Direct ELISA Test
Detects presence of a specific antigen
Monoclonal antibodies bind to bottom of the test plate.
Add the sample, antigen molecules within it will bind to the antibodies.
Rinse out excess
Add a mobile antibody with a reporter enzyme, the antibody will bind to the antigen.
Rinse out any excess
Add substrate which is complementary to reporter enzyme.
If antigen is present, colour change, if no antigen, then no colour change.
Indirect ELISA Test
Detects an antibody against a specific antigen
Antigens bind to the bottom of the test plate
Add sample, antibodies present will bind tot he antigen.
Rinse out any excess
Add secondary antibodies with reporter enzymes, these antibodies will bind to the primary antibodies.
Rinse out any excess
Add substrate, which is complementary to reporter enzyme
If antibody is present, colour change, if no antibody, no colour change.
