Cell recognition and the immune system Flashcards
How does body recognise cells
Specific molecules, mostly proteins, on cell-surface that are highly specific to pathogens, other cells, toxins and abnormal body cells, and normal body cells.
How body recognises body cells
When fetus, lymphocytes constantly colliding with other cells (exclusively with own cells).
Lymphocytes with receptors for own cells are suppressed and die.
Lymphocytes produced in bone marrow that respond to self antigens undergo apoptosis before maturing.
Phagocytosis
Chemical products of toxins and dead, damaged, abnormal cells attract phagocytes which attach to the chemicals on surface of pathogen using receptors.
Engulf pathogen to form vesicle known as phagosome.
Lysozymes then hydrolyse the bacteria and products are absorbed into cytoplasm.
Antigen
Part of organism that is recognised as non-self by immune system and stimulates response.
Usually proteins on plasma membranes of cells.
How can T-cells differentiate invader cells from normal
Phagocytes can display a hydrolysed pathogen’s antigens on surface membrane OR body cells invaded by virus can display virus antigens on surface OR transplanted cells have foreign antigens OR cancer cells present different antigens.
Cell-mediated immunity
- Pathogens invade and phagocyte places antigens from pathogen on cell-surface membrane.
- Receptors from helper T cell fit exactly to antigens and activates T cell to divide rapidly by mitosis.
- Cloned T cells develop into memory cells to enable rapid response in future, stimulate phagocytes, stimulate B cells to divide and secrete antibodies, activate cytotoxic T cells.
How do cytotoxic T cells kill
Produce protein called perforin that makes holes in cell-surface membrane to make it freely permeable, works well against viruses because sacrifice of body cells.
Humoral immunity
- Surface antigens of invading pathogen bind to complementary surface antibody on B cell and taken in by endocytosis and presented on surface.
- Activated helper T cells attach to processed antigens and activate the B cell.
- B cell then divides by mitosis to produce plasma cells and memory cells.
- Plasma cells secrete many antibodies but survive a few days and memory cells are responsible for secondary response.
What is secondary response
Future infections responded to by memory cells dividing rapidly into plasma cells that secrete antibodies to kill cell.
Antibody def
Proteins with binding complexes synthesised by B cells, complementary to a specific antigen.
Structure of an antibody
4 polypeptide chains. Two heavy chains and 2 light chains. Binding site is different on each and called the variable region that consists of sequence of amino acids to form 3D shape. Binds to form antigen-antibody complex.
Rest of antibody known as constant region. Constant region binds to receptors on B cells.
Hinge region allows flexibility to bind to more than one antigen
How does antibody help kill a pathogen
They can clump bacterial cells together (agglutination) to make them easier to locate by phagocytes as less spread out.
Can act as markers to stimulate phagocytes to engulf pathogen.
Targeting medication to cancer cells by attaching a therapeutic drug to an antibody
Monoclonal antibodies have receptors specific to cancer cells.
They attach themselves to cancer cells and block uncontrolled growth or kill cancer cells using radiation.
No side effects.
Monoclonal antibodies in medical diagnosis
Using monoclonal antibody that interacts with protein produced as a symptom of a disease means that the level of the protein as a symptom can be measured.
Monoclonal antibodies in pregnancy tests
Placenta produces a hormone hCG that can be found in urine.
Monoclonal antibodies are linked to coloured particles and binds to hCG if present. Antigen-antibody substrate complex moves across strip until stopped by different type of antibody to make coloured line.
