❌Cells structure- Cell recognition and the Immune System Flashcards
what are the two defence mechanisms?
- Innate - the non specific response which is immediate and the same for all pathogens
- Adaptive - the specific response which is slower and specific to each pathogen
give two types of innate defence mechanisms
- physical barriers like skin, ciliated epithelium, tears, mucus, saliva and conc. HCl in the stomach.
- phagocytosis
How are phagocytes and lymphocytes able to distinguish between self and non-self cells?
because each type of cell has protein receptor molecules on it’s surface
What do the protein receptor molecules on the surface of lymphocytes and phagocytes allow the immune system to identify?
- pathogens
- non-cell material e.g. cells from other organisms of the same species
- toxins including those produced by certain pathogens like the bacterium that causes cholera
- abnormal body cells such as cancer cells
How do lymphocytes recognise self cells
- in the fetus lymphocytes constantly collide with almost only self cells as infection in the fetus is rare as its protected by the placenta
- some of the lymphocytes will have receptors that exactly fit those of the body’s own cells
- these lymphocytes either die or are suppressed and remaining lymphocytes are those that fit foreign non-self cells hence only respond to them
- in adults, lymphocytes produced in the bone marrow initially only encounter self antigens and those that show immune response to self antigens undergo apoptosis hence only lymphocytes that may respond to non-self antigens appear in the blood
Explain the phagocytosis of pathogens and subsequent destruction of ingested pathogens by lysozymes
- chemotaxis by phagocytes
- protein receptors on the phagocyte recognise the pathogen as a non self cell so the phagocyte engulfs the pathogen in endocytosis
- the pathogen is contained within the phagocyte through a phagosome
- a lysosome fuses with the phagosome and releases lysozyme to digest the pathogen via hydrolysis and the pathogen dies
- the digested material is released from the phagocyte via exocytosis
Give three features of an antigen
- they are proteins that recognise as non self
- they often have proteins on the surface (antigens)
- they trigger an immune response
What does the shape specific feature of antigens mean for the immune system?
It allows the immune system to identify:
- pathogens e.g. influenza
- toxins e.g. botulism
- abnormal cells
- cells from other organisms
What are the three features of antibodies?
- They are quaternary proteins that consist of 2 heavy chains and 2 light chains
- they are highly specific so form an “antigen antibody complex” (KEY WORD)
What are the two types of adaptive mechanisms
- the cell mediated response of T lymphocytes
- the humoral response of B lymphocytes
What are antigen presenting cells?
Cells that display foreign antigens on their surface
What antigens do t lymphocytes respond to?
Antigens that are presented on a body cell rather than those within body fluids
What do plasma proteins do and how are they suited for this function?
They manufacture and secrete antibodies and are suited for this as:
- they have a larger number of ribosomes associated with a more extensive rough ER
- they have a larger Golgi
- they have more mitochondria
Give the steps of cell mediated immunity
- Pathogens invade body cells or are taken up by phagocytes
- The phagocyte places antigens from the pathogen on its cell-surface membrane (antigen presentation)
- Receptors on a specific helper T cell fit exactly onto these antigens
- This attachment activates T cells to rapidly divide by mitosis and form a clone of genetically identical cells
- The cloned T cells then:
- develop into memory cells that enable a rapid response to future infections by the same pathogen
- stimulate phagocytes to engulf pathogens by phagocytosis
- stimulate B cells to divide and secrete their antibody
- activate cytotoxic T cells
How do cytotoxic T cells work?
They kill abnormal cells and body cells infected by pathogens by producing the protein perforin which makes holes in the cell surface membrane causing it to become freely permeable hence the cell dies. It’s most effective against viruses as it prevents them from being able to replicate
What do monoclonal antibodies develop into? Give a description of each
- Plasma cells: secrete antibodies which destroy antigens (forms the primary immune response which is the production of antibodies and memory cells)
- Memory cells: circulate in blood and tissue fluid and divide rapidly into plasma cells which produce the antibodies and memory cells when an antigen that has previously entered the body returns so form part of the secondary immune response
Describe the steps of humoral immunity
- The surface antigens of an invading pathogen are taken up by a specific B
- The B cell processes the antigen and presents them on its surface
- Helper T cells from the cell mediated immunity attach to the processed antigens on the B cell hence activating the B cell by releasing cytokines cell causing it to divide by mitosis to give a clone of plasma cells
- The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
- The antibody attaches to antigens on the pathogens and destroys them through agglutination, opsonisation, neutralisation and inactivation via antigen antibody complexes
- Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies (this is the secondary immune response).
What are the 4 ways antibodies work?
- release metabolic toxins
- cause agglutination which makes it easier for phagocytes to locate the pathogen as it isn’t as spread out within the body
- serve as markers in opsonisation as they stimulate the phagocytes to engulf the pathogen to which they are attached
- they inactivate viruses