Immunity Flashcards
What happens as a B cell matures?
- As a B cell matures it gains the ability to make just one type of antibody moelcule
- While B cells are maturing, the genes that code for antibodies are changed in a variety of ways to code for different antibodies
- Each cell then divides to give a small number of cells that are able to make the same type of antibody
- Each small group of identical cells is called a clone
What happens after a clone is formed?
- At this stage the antibody molecules do not leave the B cell but remain in the cell surface membrane, here, part of each antibody forms a glycoprotein receptor, which can combine specifically with one type of antigen
- If that antigen enters the body, there will be some mature B cells with cell surface receptors that will recognise it
What happens when the antigen enters the body?
- When the antigen enters the body for the first time the small numbers of B cells with receptors complementary to the antigen are stimulated to divide by mitosis
- This stage is known as clonal section
- The small clone of cells divides repeatedly by mitosis in the clonal expansion stage so that high numbers of identical B cells are produced over a few weeks
What are plasma cells?
- Some of these activated B cells become plasma cells that produce antibody molecules very quickly, up to several thousand a second
- Plasma cells secrete antibodies into the blood, lymph or onto the lines of the lungs and the gut
- These plasma cells do not live long; after several weeks their numbers decrease
- The antibody molecules they have secreted stay in the blood for longer, however until they too eventually decrease in concentration
What are memory cells?
- Other B cells become memory cells
- These cells remain circulating in the body for a long time
- If the same antigen is reintroduced a few weeks or months after the first infection, memory cells divide rapidly and develop into plasmas cells and more memory cells
- This is repeated in every subsequent invasion by the same antigen, meaning that the infection can be destroyed and removed before any symptoms of the disease develop
What is the primary and secondary response?
- The primary response is slow because, at this stage there are very few B cells that are specific to the antigen
- During the primary response the number of cells in each clone of B cells that is selected has increased in size. There are many more B cells specific to the pathogen that has invaded the body. Many more antibodies are produced in the secondary response - The secondary response is faster because there are now more memory cells, which quickly divide and differentiate into plasma
What is your immunological memory?
- Memory cells are the basis of immunological memory; they last for many years, often a lifetime (this explains why someone is very unlikely to catch measles twice)
- There is only one strain of the virus that causes measles, and each time it infects the body there is a fast secondary response
- However repeated infections of the common cold and influenza, because there are many different new strains of the viruses that cause these diseases, each one having different antigens
- Each time a pathogen with different antigens infects us, the primary response emus occur before we become immune, and during that tine we often become ill
What are T-lymphocytes?
- Mature T-cells have specific cell surface receptors called T cell receptors
- T cell receptors have a structure similar to that of antibodies and they are each specific to one antigen
What is antigen presentation?
- T-cells are activated when they encounter this antigen on another cell of the host (that is, on the person’s owns cells)
- Sometimes this cell is a macrophage that has engulfed a pathogen and cut it up to expose the pathogen’s surface molecules, or it may be a body cell that has been invaded by a pathogen and is similarly displaying the antigen on its cell surface membrane as a kind of ‘help’ signal
- The display of antigens on the surface of cells in this way is known as antigen presentation
- Those T-cells that have receptors complementary to the antigen respond by dividing by mitosis to increase the number of cells
- T cells go though the same stages of clonal selection and clonal expansion as clones of B cells
What are the two main types of T cell?
- Helper T cells
2. Killer T cells (or cytoxic T cells)
What happens when helper T cells are activated?
- They release hormone-like cytokines that stimulate appropriate B cells to divide, develop into plasma cells and secrete antibodies
- Some T helper cells secrete cytokines that stimulate macrophages to carry out phagocytosis more vigorously
What do killer T cells do?
- Killer T cells search the body for cells that have become invaded by pathogen and are displaying foreign antigens from the pathogen on their cell surface membranes
- Killer T cells recognise the antigens, attach themselves to the surface of infected cells, and secrete toxic substance such as hydrogen peroxide, killing the body cells and the pathogens inside
What is another role of helper T cells? What are memory cells in T cells like?
- Some helper T cells secrete cytokines that stimulate macrophages to carry out phagocytosis more vigorously, or that stimulate killer T cells to divide by mitosis and to differentiate by producing vacuoles full of toxins
- Memory helper T cells and memory killer T cells are produced, which remains in the body and become active very quickly during the secondary response to antigens
What are antibodies?
- Antibodies are globular glycoproteins with quaternary structure
- They form a group of pals proteins called immunoglobulins
What is the basic molecule of antibodies like?
- The basic molecule common to all antibodies consists of four polypeptide chains: two “long” or “heavy” chains and two “short” or “light” chains
- Disulphide bonds hold the long/heavy chains together
- Each molecule has two identical antigen-binding sites, which are formed by both light and heavy chains
- The sequence of amino acids in these regions make the specific 3D shape which bonds to just one type of antigen
What is the variable region of an antibody?
- The antigen-binding sites form the variable region, which is different on each type of antibody molecule produced (specific)
- The ‘hinge’ region gives the flexibility for the antibody molecule to bind around the antigen
What are the different types of phagocytes? Where are they produced?
- Phagocytes are produced throughout the life in the bone marrow and they are stored there before being distributed around the body in the blood
- Neutrophils, macrophages and monocytes
- Phagocytes have their origin in the bone marrow
What are neutrophils?
- They from about 60% of the white blood cells in the blood
- They travel throughout the body, often leaving the blood through the walls of capillaries to ‘patrol’ the tissues
- During infection neutrophils are released in large numbers from their stores, but they are short-lived cells
What are macrophages?
- They are larger than neutrophils and tend to be found in organs such as the lungs, liver, spleen kidneys and lymph node, rather than remaining in the blood
- After they are made in the bone marrow macrogphages travel in the blood as MONOCYTES, which develop into macrophages as they leave the blood and settle in the organ, removing any foreign matter found there
- Macphages are long-lived cells and play a crucial role in initiating the immune response, since they do not destroy pathogens completely, but cut them up to display antigens that can be recognised by lymphocytes
Describe the stages of phagocytosis
- Attraction (chemotaxis)
- Recognition and attachment
- Endocytosis
- Bacteria within a phagocytic vacuole
- Fusion of lysosomes and phagocytic vacuole
- Killing and digestion
What happens during phagocytosis?
- If pathogens invade the body and cause an infection, some of the cells under attack respond by releasing chemicals such as histamine
- These, with any chemicals released by the pathogens themselves, attract passing neutrophils to the site and this movement towards a chemical stimulus is called chemotaxis
- The neutorphils destroy the pathogens by phagocytosis
How do neutrophils act in phagocytosis?
- The neutrophils move toward the pathogen, which may be clustered together and covered in antibodies
- The antibodies further stimulate the neutorphils to attack the pathogens
- This is because neutrophils have receptor proteins on their surfaces that recognise antibody molecules and attach to them
- When the neutrophil attaches to the pathogen, the neutrophil’s cell surface membrane engulfs the pathogen and traps it within a phagocytic vacuole, in a process called endocytosis
- Digestive enzymes are secreted into the pahgocytic vacuole, so destroying the pathogen
- Neutrophils have a short life: after killing and digesting some pathogens, they die. Dead neutorphils often collect at a site of infection to form pus
What is an antigen?
An antigen is a substance that is foreign to the body and stimulates and immune response
What is an antibody?
An antibody is a glycoprotein (immunoglobulin) made by plasma cells derived from B-lymphocytes, secreted in response to an antigen; the variable region of the antibody molecule is complimentary in shape to its specific antigen
What is the immune response?
The immune response is the complex series of responses of the body to the entry of a foreign antigen; it involves the activity of lymphocytes and phagocytes
What is non-self?
Non-self refers to any substance or cell that is recognised by the immune system as being foreign and will stimulate an immune response
What is self?
Self refers to substances produced by the body that the immune system does not recognise as foreign, so they do not stimulate an immune response
What are the two types of white blood cells?
- Lymphocytes
2. Phagocytes (e.g. neutrophils and macrophages)
When do the number of white blood cells increase in the body?
- The number of neutrophils in the blood increases during bacterial infections and whenever tissues become inflamed and die
- The number of lymphocytes in the blood increases in viral infections and in TB
- Most of the lymphocytes that circulate in the blood are T cells
Where do the white blood cells originate from?
- Myeloid Stem cells in the bone marrow, give rise to monocytes, neutrophils and platelets
- Lymphoid Stem cells in the bone marrow give rise to lymphocytes, both B and T cells