Immune System Flashcards
What are lymphocytes?
- Cells that are part of the immune system
- Identify the presence of pathogens and harmful foreign substances to then destroy or neutralise them
Identifying self and non-self cells?
- Each type of cell has specific molecules on their surface that identify it. These molecules are usually proteins as the 3D tertiary structure allows for lots of unique and identifiable shapes to be made
- If a non-self cell is identified, a response is triggered to destroy it.
What can lymphocytes identify due to different surface molecules?
- Pathogens (bacteria, fungi, HIV)
- Cells from other organisms of the same species (harmful for those with organ transplants)
- Abnormal body cells (cancer cells)
- Toxins - some pathogens release toxins into the blood (cholera)
What’s an antigen?
- molecules that generate an immune response by lymphocyte cells when detected in the body
- usually proteins
- located on the surface of cells
What’s antigen variability?
- Pathogens DNA can mutate frequently - mutations in general coding for antigen = change antigen shape
- Previous immunity to pathogens no longer effective - all memory cells have old antigen shape (influenza virus, flu jab)
What’s the second line of defense in the immune response?
- If a pathogen gets past chemical and physical barriers (skin and stomach acid) and enters the blood then white blood cells are the second line of defense
- White blood cells have specific and non-specific responses
What’s the white blood cells specific response?
Lymphocytes
What’s the white blood cells non-specific response?
Phagocytes
What is a phagocyte?
- Macrophage (white blood cell) that does phagocytosis
- In blood and tissues
Steps of Phagocytosis?
- Non-specific response - same response to destroy anything
1. Many receptor binding points on the surface. Attach to chemicals or antigens on pathogen via these receptors.
2. Phagocyte changes shape to move around and engulf the pathogen
3. Once engulfed, pathogen contained within phagosome vesicle
4. Lysosomes within phagocyte fuse with phagosome and release its contents
5. Lysozyme enzyme released into phagosome - hydrolyses pathogen
What are T lymphocytes?
- All lymphocytes are made in bone marrow, but T cells mature in thymus
- Cell-mediated response involves T cells and body cells
What’s the cell mediated response?
- Involves T cells and body cells
- Once pathogen is destroyed, antigens are positioned on the cell surface - Antigen Presenting Cell (APC)
- Helper T cells have receptors on their surface which attach to antigens on the APC
- Once attached this activates the helper T cells to divide by mitosis to replicate and make clones
What cell can cloned helper T cells differentiate into?
- Some remain as helper T cells and activate B lymphocytes
- Some stimulate macrophages for more phagocytes
- Some become memory cells for that shaped antigen
What are B lymphocytes?
- B cell made in and mature in bone marrow
- Humoral response involves B cells and antibodies
- Antibodies are soluble and transport in bodily fluids
Steps of B cell activation?
- B cell is triggered when it encounters its matching antigen
- B cell engulfs antigens on APC and digests it
- Displays antigen fragments bound to its unique MHC molecules
- Combination of antigen and MHC attracts help of mature matching T cells
- Cytokinesis secreted by T cell helps the B cell to multiply and mature into an antibody, producing plasma cells
- Released into the blood, antibodies lock onto matching antigens - Antigen-antibody complex.
What are memory B cells?
- Live for decades
- Don’t make antibodies - instead divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered
- Results in a large number of antibodies being produced so fast that pathogen is destroyed before any symptoms can occur
Antibody structure?
Quarternary structure protein - 4 polypeptide chains:
- Variable region
- Light chain
- Heavy chain
- Constant region
What is agglutination?
Antibodies are flexible and can bind to multiple antigens to clump them together - easier for phagocytes to locate and destroy the pathogens
What is MHC?
Major Histocompatibility Complex
