Immunity Flashcards
Where do Phagocytes originate from
Bone marrow. Macrophages and neutrophils
Macrophages
When immature they are monocytes in blood, they are in the organs. They cut up antigens and display them for lymphocytes to recognise.
Neutrophils
Found in the blood, released in large numbers when there is an immune response
Phagocytosis
Attraction (chemotaxis). The bacterium attaches to the phagocytes membrane as they have receptor proteins which recognise antigens and can attach to them. Endocytosis, the phagocyte’s cell surface membrane engulfs the pathogen and traps it within a phagocytic vacuole. The lysosome fuses with the phagocytic vacuole, digestive enzymes are secreted with the phagocytic vacuole which destroys the pathogen.
Immune response
The complex series of responses of the body to the entry of foreign antigens, it involves the activity of lymphocytes and phagocytes. It involves the ability to distinguish between self and on-self cells and only attack non-self cells.
What do B lymphocytes do during a immune response
The B cell which has an antibody complimentary to the antigen divides by mitosis in a process called clonal selection. This small clone of cells divides repeatedly by mitosis during clonal expansion. Some become plasma cells which produce antibodies. Others become memory cells.
What is the significance of memory cells
They allow for a more rapid response and for more antibodies to be produced. The memory cells remain in the blood for a long time and if they encounter the same antigen again they divide rapidly to produce plasma cells and more memory cells. So that the infection can be destroyed before any symptoms are shown. They are the basis for immunological memory.
How are T cells activated
All T lymphocytes are activated when they in-counter an antigen displayed on a persons cell. This may be a macrophage who is doing antigen presentation. Or it could be a body cells which has been invaded by a pathogen and is displaying the antigens. They then go through clonal selection and expansion.
What do helper T cells do
They release cytokines which stimulates appropriate B cells to divide, develop into plasma cells and secrete antibodies. The cytokines may stimulate the macrophages to carry out phagocytosis more vigorously. Some helper T cells divide to form memory cells. Some secrete cytokines which stimulate killer cells to divide by mitosis and differentiate by producing vacuoles full of toxins.
What do killer T cells do
When they recognise the antigen on the infected body cell, they attach themselves and secrete toxic substances like hydrogen peroxide to kill the body cell and the pathogen inside. Some divide by mitosis to form memory cells.
What happens to the white blood cell count of people with infectious diseases
The number of neutrophils in the blood increases during bacterial infection. The number of lymphocytes in the blood increases during viral infection and TB. In HIV the number of T lymphocytes decreases as the virus kills T-cells.
What happens in leukaemia?
Leukaemia is the cancer of the stem cells. Myeloid stem cells give rise to neutrophils, monocytes and platelets. Lymphoid stem cells give rise to lymphocytes. In myeloid leukaemia the stem cells responsible for producing neutrophils divide uncontrollably and the number of immature cells increases. In lymphoblastic leukaemia the cancerous cells are those that give rise to lymphocytes.
What happens to the white blood cell count of people with Leukaemia?
The number of immature white blood cells are produced very quickly and disrupt the normal balance of components in the blood. The number of mature neutrophils and lymphocytes decrease. As well as the number of platelets and red blood cells.
What is the structure of antibodies
They are globular glycoproteins with a quaternary structure. They have 4 polypeptide chains, 2 short and 2 long. Each molecule has 2 identical antigen binding sites. The sequence of amino acids makes the specific 3 dimensional shape which binds to one type of antigen. The antigen binding site forms the variable region which is different for each antibody. The hinge region gives the antibody flexibility around the antigen
Function of antibody
Combines with viruses and bacterial toxins to prevent them entering and damaging the body. Attach to flagella of bacteria making them less active and easier for phagocytes to engulf. Clump bacteria together to stop them spreading through the body. Punch holes in the cell wall of bacteria to cause them to burst when water enters by osmosis.
