Cell recognition and the immune system Unit 2.4 Flashcards
What is a pathogen? + examples
-Organism that causes disease and a immune response
-for example bacteria, fungi, viruses and parasites
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How do pathogens cause disease?
-By destroying cells and releasing toxins
What is an antigen?
- A molecules usually a protein with a specific tertiary structure
- Found on surface of cells
- Antigens not found on your body are referred to as non self or foreign - these generate an immune response
What is the immune system able to recognise?
Antigens allow the immune system to identify:
- Pathogens eg. bacteria viruses and fungi
- Abnormal body cells eg. Cancerous cells or cells infected by pathogens like cholera
- Cells from other organisms
What are non-specific defence mechanism of the body?
- Response is immediate and same for all pathogens
1. Physical barrier eg. skin and hydrochloric acid
2. Phagocytosis eg. white blood cells engulf and digest pathogens
What are 3 of our first line of defence against pathogens and how to they work
- Hydrochloric acid - Destroys pathogens in food (denatures them)
- Mucus - Traps pathogens
- Skin - forms impenetrable barrier
What are Specific defence mechanisms for the body
- Responses are slower and specific to a particular pathogen
1. Cellular response eg. T-lymphocytes
2. Humoral response eg. B-lymphocytes
What occurs in Phagocytosis? 6 points
- Phagocytes (white blood cells) recognise foreign antigens on a pathogen
- The pathogen is engulfed by the phagocyte
- Engulfed pathogen is contained in a vesicle known as a phagosome or phagocytic vacuole
- Lysosomes fuse with the vesicle releasing lysozymes (digestive enzymes) into the phagosome
- The digestive enzymes hydrolyse the molecules in the pathogen by breaking large insoluble molecules into smaller soluble molecules
- The antigens are presented on the cell surface membrane
What is clonal selection?
- A specific T-cell binds to presented antigen via its complimentary receptor
- T-cell is activated and produces many clones by mitosis to form T- cells with receptors complimentary to antigen
- They become either TH or TC cells
What occurs in cellular response
-Antigen presenting cell activates specific T-cells
T-cells clone by mitosis to form:
-Cytotoxic T-cells which kill infected cells
- OR Helper T-cells which stimulate cytotoxic T cells, B cells and phagocytes
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What is a B lymphocyte(B cell)?
-A white blood cells responsible for producing millions of B cells - each produces a special antibody
How are specific B cells activated?
Specific B cells has protein receptors complimentary to:
- Antigen presented by phagocytes
- Receptor on activated T helper cell
When bound to the these the B cell is activated
What occurs in humoral response
- Specific T helper cells activate B cells
- B cells then clone by mitosis to form either:
1. Plasma cells which secrete antibodies
2. Memory cells
What is the secondary immune response?
- Secondary response faster than primary response
- Secondary response produces more antibodies than primary response
What is an antibody?
- A quaternary protein with a binding site complimentary to one antigen
- Produced by plasma cells
- Form ANTIGEN ANTIBODY COMPLEXES
- Contains a disulphide bond, a constant region, 4 polypeptide chains and a variable region
