The Immune Response Flashcards
What is the first line of defence?
Natural barriers to infection
Why is the skin a natural barrier?
Forms a tough barrier (collagen) to prevent entry, vitamin C is required to maintain barrier
Why is the skin flora a natural barrier?
Compete with pathogenic bacteria preventing them from growing, the gut and other areas also have their own flora
Why is blood clotting a natural barrier?
Seals wound to prevent entry of pathogens
Why is inflammation a natural barrier?
Cells surround the site of infection to prevent the spread of disease
Why is phagocytosis a natural barrier?
Invading microbes are engulfed and destroyed
Why is the mucus membrane a natural barrier?
Mucus and ciliated cells trap microbes and help remove them
Why are acid and lysozyme natural barriers?
Stomach acid kills bacteria
Lysozyme in tears and saliva hydrolyses the peptidoglycan in bacterial cell wall
What is the second line of defence?
Once past the barriers, the immune system uses phagocytosis and inflammation to trap and destroy invaders
What are the signs of inflammation?
- redness
- heat
- pain
- swelling
What are the functions of inflammation?
- increases blood flow to the area
- destroy the cause of infection
- repair/replace damaged tissue
What are the steps of phagocytosis?
- Pseudopodia surround pathogens
- Pathogens are engulfed by endocytosis
- Vacuole forms, enclosing pathogens
- Vacuole and lysosome fuse
- Toxic compounds and lysosomal enzymes destroy pathogens
- Debris from pathogens is released by exocytosis
What are phagocytes?
Cells which engulf and destroy microbes and dead cells e.g macrophages or neutrophils
What are lymphocytes?
Involved in the specific immune response and come in two main types - B lymphocytes and T lymphocytes
What are B lymphocytes?
Mature in the spleen and lymph nodes and produce antibodies
What are T lymphocytes?
Mature in the thymus and come in 2 main types - T helper or T killer
What is the specific immune response?
This is a response to an antigen involving lymphocytes, an antigen is a molecule that elicits an immune response, usually parts of proteins
Can be humoral (B lymphocytes) or cell mediated (T lymphocytes)
What is the humoral response?
- each B lymphocyte has a different antigen receptor or binding site
- each one will make antibodies similar to this receptor which will attach to this specific antigen
- when a B lymphocyte is stimulated by their specific antigen on an antigen-presenting cell they develop into 2 types of cells:
Plasma cells (produce antibodies and die shortly after)
Memory cells (remain in the body for months or years in case the same antigen appears)
What are antigens?
- substances that are recognised as foreign by immune system
- specific shape
- stimulate an immune response
- usually proteins - polysaccharide or glycoprotein
Can be:
- on surface of bacteria/virus
- on cell surface of foreign tissue
- free molecules
What is the structure of antibodies?
- Quaternary globular proteins
- Y shape made of 4 polypeptide chains
- Chains are held together by disulphide bonds
- 2 antibody binding sites which are specific to antigen
- Phagocytes can bind to the constant region (helps phagocytosis)
What is opsonisation?
- Antibodies bind to antigens on microbes
- Phagocytes have receptors which enable them to bind to and engulf microbes coated with antigen
What is agglutination?
Formation of antibody-antigen complexes the pathogens are held together in large clumps
- Prevents pathogens from moving and invading cells
- Macrophages and neutrophils more easily engulfed
What is the cell mediated response?
- Specific antigens on antigen processing cells stimulate the T lymphocytes to proliferate
- T helper activate both B + T lymphocytes and phagocytes. Release cytokines
- T killer cause lysis of infected cells or invading cells
- Memory cells are produced for both types
What is clonal selection and expansion?
- Binding of antigen to the receptor will stimulate one or more cells (selection) to undergo mitosis producing clones (expansion)
- most become antibody producing plasma cells
- some remain as memory cells
- similar process happens in T lymphocytes
- cytokines activate both cell types
