12.6 - The Specific Immune System Flashcards
What are antigens, and how does the body respond to them?
- All cell molecules have antigens (identifying chemical on the surface if a cell that triggers immune response)
- The body recognises the difference between self and non-self antigens.
- Antigens trigger an immune response, involving the production of polypeptides antibodies (Y shaped glycoproteins made by B-cells of immune system in response to antigen presence)
Describe the structure of an antibody.
- Made of 2 identical polypeptide chains called heavy chain and 2 shorter identical chains called light chain
- Chains held together by disulphide bonds, there are these bond within the polypeptide chains to hold them in shape
- Antibodies bind to antigens, similar to ‘lock and key’ hypothesis due to the complementarity between antibody and antigen.
- Antigen binding site, are of 110 aas on both heavy and light chains known as variable region
- Different variable region shape give the antibody specificity.
- The constant region is the same between all antibodies. The hinge region gives flexibility to allow molecule to bind to 2 separate antigens, on at each antigen binding site.
What happens when antibodies and antigens interact?
- Known as immunoglobulins – bind to specific antigen on pathogen or toxin that triggered the immune response
- There are many antibodies – specific antibody per antigen (complementary molecules)
- Antigen-antibody complex: Complex formed when antigen binds to antibody (Ag-Ab complex)
How do antibodies defend the body?
- Antibody of the antigen-antibody complex acts as an opsonin, so the complex is easily identified, engulfed and digested by the phagocyte.
- Pathogens can no longer invade host cells once bound in the antigen-antibody complex
- Antibodies act as agglutinins – cause pathogens to bind to clump together so it is easier for the phagocyte to engulf a large quantity of pathogen at once.
What are the different types of lymphocytes?
Specific immune system based on white blood cells called lymphocytes
B-lymphocytes – mature in Bone marrow
T-lymphocytes – mature in Thymus gland
What are the different types of T- and B- Lymphocytes?
- T Helper
- T Killer
- T Regulator
- T Memory
- Plasma Cells
- B Memory
- B effector
What are the roles of:
T killer cells
T helper cells
T HELPER
- Have CD4 receptors on plasma membranes, bind to antigens of APCs
- Producing interleukins - type of cytokine (cell signalling molecule)
- Interleukins made by T helpers, stimulating B-cell activity - increasing antibody production, stimulates other T-cells and attracts/stimulates macrophages to ingest pathogens with AAC
T-KILLER
- Destroy pathogen carrying the antigen
- Produce perforin (chemical), kills pathogens by making holes in cell membrane > making it freely permeable
What are the roles of the different B-lymphocytes?
PLASMA CELLS
- Produce antibodies to particular antigen
- Short lifespan, produces 2000 antibodies per second
B EFFECTOR CELLS
- Divide and form plasma cell clones
B MEMORY CELLS
- Long lifespan
- Provide immunological make memory
- Programmed to remember specific antigen, enable the body to raipd secondary response
Why is cell mediated immunity important?
T-lymphocytes respond to altered (cell mediated) cells. E.g. APCs (antigen processing), cancer (mutations), virus. Cell mediated response is important against viruses and early cancers
Describe the process of cell-mediated immunity?
- In non-specific defence, macrophages engulf and digest pathogens in phagocytosis – process pathogen antigen, create APCs
- CD4 receptors on T-helper cells fit to the antigens on APCs. TH cells activated and interleukins are secreted.
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Interleukins stimulate T cells to proliferate by mitosis - each new TH cell is activated and carrying the right antigen to bind to a pathogen.
* Cloned TH cells will…
Develop into T-memory cells - gives rapid 2o response. Produce interleukins to stimulate phagocytosis.
- Produce interleukins to stimulate B cells to form plasma cells.
- Stimulate clone T-killer cells that are specific to antigens and then destroy infectected cells (perforin)
What is the difference between cell-mediated and humoral immunity?
Cell mediated immunity and humoral immunity is T-lymphocytes are used for the former and B-lymphocytes used for the latter.
T-lymphocytes can only recognise antigens bound to MHC on APC surface (altered cells)
B-lymphocytes can recognise Ag-MHC as well as free pathogens in the body
Millions of B-lymphocytes with different antibodies, when a pathogen enters the body, its specific antigens/toxins will be recognised by a B-cell with complimentary antibodies. B-cell engulfs and processes the antigens to become an APC.
Describe the process of humoral immunity.
- Clonal selection: Activated T-helper cells bind to B-APC, B cell with correct antibodies for the antigen are selected for cloning
- Interleukins provided by activated T-helper cells activate B cells
- Activated B cells proliferate by mitosis (clonal expansion) to form plasma and B-memory cells.
- 1o response: cloned plasma cells produce complematary antibodies to bind and disable antigens or act as opsonins/agglutinins
- Time is taken for the primary response to be effective against pathogens, hence getting ill and symptoms - pathogens constantly dividing
- B cells develop into B memory cells, if the body is infected by same pathogens, BM cells rapidly divide to form plasma cell clones and antibodies produced much quicker. 2o response.
What are autoimmune diseases and their characteristics?
Autoimmune disease: Condition or illness where the immune system stops recognises self-cells and starts attacking its own healthy tissue in the body.
- Unknown cause – there are genetic tendencies, immune system may react abnormally to mild pathogens or normal body microorganisms.
- T-reg. cells may not function effectively
- 80 different autoimmune diseases, causes chronic inflammation or breakdown of healthy tissue
- Immunosuppressant drugs can be used, but they stop the body of its natural defence against communicable disease.
Give some examples of autoimmune diseases.
Type 1 Diabetes - affects insulin secreting cells of pancreas (ß cells), cure of immunosuppressants, insulin injections, pancreas transplant
Lupus - affects skin and joins causing fatigue, attacks any organ.
No cure, take pain relief, immunosuppressants, anti inflammatory drugs
Rheumatoid - Affects joints, same cures as Lupus
