Non Bacterial Pathogens Flashcards
What is an antigen
An antigen is any substance that stimulates an immune response in the body. Antigens are often chemicals on the surface of a cell such as proteins, glycoproteins or carbohydrates
What is the difference between non specific and specific responses
Non specific responses are triggered by any pathogen whereas specific responses are specific to a particular pathogen
What are the different stages to inflammation
Special cells called mast cells are found in the connective tissue below the skin and around blood vessels. When this tissue is damaged these mast cells and basophils release chemicals known as histamines. Histamines cause the blood vessels in the area particularly the arterioles to dilate causing local heat and redness. The locally raised temp reduces the effectiveness of pathogen reproduction in the area. They also make the walls of the capillaries leaky as the cells forming the walls separate slightly. As a result plasma containing leucocytes and antibodies of forced out of the capillaries causing swelling and often pain. The antibodies disable the pathogen and the macrophages and neutrophils destroy them by phagocytosis
What are the different stages to fevers
When a pathogen infects the body it causes the hypothalamus to reset to a higher body temp so that we become aware we have a fever. A raised temp helps the body to combat infection in two ways. Many pathogens reproduce most quickly at 37°c or lower therefore a raised temp will reduce the ability of many pathogens to reproduce effectively. The specific immune response works better at a higher temp. In bacterial infection temp rises steadily but with viral infections it spikes up and down.
What are the 2 main types of phagocyte
- Neutrophils and granulocytes make up 70% of the leucocytes in the blood. Each neutrophil can only ingest a few pathogens before it dies. They can’t renew their lysosomes so once the enzymes are used up the cell cannot break down any more pathogens.
- Macrophages are derived from monocytes which are agranulocytes. They make up 4% of the Leucocytes in the blood. However the monocytes migrate to the tissue and become macrophages in the tissues. Macrophages have an enormous capacity for ingesting pathogens because they can renew their lysosomes.
How does phagocytosis take place
The phagocytes engulf the pathogen. The pathogen is enclosed in a vehicle called a phagosome. The phagosome then fuses with a lysosome. The enzymes in the lysosome break down the pathogen. When the phagocytes have engulfed a pathogen they produce chemicals called cytokines in the surrounding tissue
What are the 4 key characteristics of the immune system
- it can distinguish self from non self
- it is specific it responds to specific foreign cells
- it is diverse it can recognise an estimated 10 million different antigens
- it has immunological memory once you have met and responded to a pathogen you can respond rapidly if you meet it again
What are B cells and what are they used for
B cells are produced in the bone marrow and once mature they are found in the lymph glands and free in the body. B cells have globular receptor proteins on their cell surface membrane that are identical to the antibodies they will later produce. Around 100 million B cells are formed as an embryo grows each with a different membrane bound antibody. When a B cell binds to an antigen three types of B cell are produced B Effector cells - these cells divide to form the plasma cells clones, Plasma cells - these produce antibodies to a particular antigen and B memory cells - these provide the immunological memory to a specific antigen
What are T cells and what are they used for
T cells are produced in the Bone marrow but mature and become active in the thymus gland. The surface of each T cell displays thousands of identical T cell receptors. T cell receptors bind to antigens on infected body cells and then several further types of T cells are produced. T killer cells - produce chemicals to destroy infected body cells, t helper cells - activate the plasma cells to produce antibodies against the antigens and t memory cells - are very long lived cells that make up part of the immunological memory. When they meet a pathogen for the second time they divide rapidly.
What is the humoral response
The humoral response reacts to antigens found outside the body cells including antigens on pathogens and to antigen presenting body cells. The humoral response consists of two stages the t helped activation stage and the effector stage
What happens in the t helper activation stage
A macrophage separates off the antigens from the digested pathogen and combines them with the major histocompatibility complex. The complexes move to the surface of the macrophage cell outer membrane. The macrophage with these antigen/MHC complexes displayed on the cell is now known as an antigen presenting cell. Then T helper cells which have receptors on the outer membrane that bind to the specific antigen of the antigen/MHC complex on the APC. The binding of the T helper cell with the APC triggers the T helper cell to reproduce and form a clone of cells. Most of these cloned cells become active t helper cells which are then used in the rest of the immune system the remainder form t memory cells
What happens in the effector stage
Some of the millions of different B cells will have immunoglobulins on their surfaces that are specific for the antigen presented by the pathogen and will bind to it. The B cell with the complementary receptor then engulfs the whole pathogen by endocytosis. As with the macrophage the vesicles formed fuses with the lysosome and enzymes break down the pathogen to leave fragments of processed antigen. These fragments become attached to the MHC proteins and the antigen complex is transported the to cell surface membrane where the antigen is displayed. A T helper cell from the active clone produced in the t helper activation stage recognises the specific antigen displayed on the MHC complex on the B cell and binds to it. This triggers the release of cytokines from the t helper cell which stimulates the B cells to divide and form clones of identical cells. This is clinal selection. The b effector cells differentiate to form plasma cells and they secrete antibodies. That are identical to the proteins of the original parent B cell.
What are the 3 ways antibodies can destroy pathogens
Agglutination - when antibodies bind to the antigens on pathogens the microoganisms agglutinate or clump together
Opsonisation- the antibody acts as an opsonin a chemical which makes an antigen or pathogen more easily recognised by phagocytes
Neutralisation- antibodies neutralise the effects of bacterial toxins by binding to them
What happens in the cell mediated response
When a body cell is infected with a bacterium or virus the pathogen is digested and the surface antigens become bound to an MHC in a similar process to that seen in macrophages. As a result the body cell becomes an APC. T killer cells present in the blood bind to the matching antigen/MHC complex on the surface of the body cell. If the T cells are then exposed to cytokines from an active t helper cell through T cell activation they undergo a rapid series of cell divisions to produce a clone of identical active t killer cells which can bind to infected body cells. The t killer cells release enzymes which make pores in the cell membrane which allows water to entry and cause lysis. T killer memory cells are also produced
