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(2nd Line of Defence (aka innate immune system = non-specific), 3rd Line…
2nd Line of Defence (aka innate immune system = non-specific)
1) Granulocytes of Basophils and Mast Cells release histamine in response to infection leading to increase redness, heat, swelling and pain.
Increased temprature slows the growth and replication of pathogens (enzymes need ideal temps to replicate).
The higher the temprature, the harder its is for the pathogen to survive.
Increase temprature enhances cell activity
When the bacterial infection is severe, white blood cells/macrophages release pyrogens that signal to the hypothalamus to raise the body's thermostat, resulting in a systemic fever. The increase in tempreture:
Increased temprature slows the growth and replication of pathogens (enzymes need ideal temps to replicate).
The higher the temprature, the harder its is for the pathogen to survive.
increases the metabolic rate of the bodies cells so they can heal faster (produces heat as a byproduct).
Histamine enables vessels to become larger via vasodiolation to increase blood flow to the area.
Histamine additionally increases the permeability of blood capillaries/vessels to enable increase blood flow tot he area and for immune response cells such as phagocytes and neutrophils to easily travel to the infected/injured area.
2) Additionally basophils and mast cells release cytokines which act as communication between cells, signalling for phagocytes such as neutrophils (which are a type of white blood cell found sitting in the blood stream and produced in the bone marrow), and macrophages (can be fixed in tissue or found in bloodstream and made in the bone marrow - known as monocytes during this stage) to travel toward the site of infection to destory bacteria - this is known as leukocytosis.
Neutrophils are the most abdundant type of white blood cell and are typically the first cells to respond to the acute infection and phagocyte pathogens. However, neutrophils often die after phagocytosis which is known as apoptosis, which is a form of programmed cell death. The neutrophils additionally:
release cytokines to attract other immune cells (backup).
release hydrogen peroxide which disrupts bacterial and fungal cell membranes, killing them.
Macrophages (another type of white blood cell) additionally perform phagocytosis, however, unlike neutrophils, they do not die after this process but rather can perform it over and over again, often with mutliple bacterium at once.
Phagocytosis:
This process involves the macrophage capturing bacterium using cytoplasmic extensions engulfing the bacterium, forming a phagosome.
The lysosome (a membrane-bound sac containing digestive enzymes) fuses with the phagosome, forming a phagolysosome.
Within the phagolysosome the enzymes break down the foreign material (bacterium) into smaller pieces.
The small waste fragments are expelled from the phagocyte (macrophage in this instance) by exocytosis.
This residual vesicle fuses with the plasma membrane and the contents are released.
Dendritic cells also aid in performing phagocytosis, however, primarily serve in the third line of defence.
3) The Complement System (non-specific) is a set of more than 30 proteins that float around in the blood and becomes activated once pathogens break through the barriers to infection. They help by:
marking pathogens for destruction aka opsonization (Opsonization is a process where proteins called opsonins coat pathogens, marking them for easier destruction by phagocytic cells, like macrophages and neutrophils)
punching holes in the cell membrane or wall of the pathogen (lysis)
further promotes inflammation
4) Natural Killer Cells constantly patrol the body, and are important in defence against virus-infected and cancerous cells. They release cytotoxic chemicals which can kills cells directly (these are only released when they're in close proximity to the target cell). They serve to kill any cell that is infected with virus or are cancerous (apoptosis - programmed cell death).
Example: Perforin punches holes in the cell membrane of the target cell, killing it.
3rd Line of Defence (aka the adaptive immune system = specific)
Antibody-mediated immunity (humoral immunity)
B Lymphocyte
Life Cycle of a B Lymphocyte:
Are Produced in the bone marrow and stay there to mature.
Once they have matured they are released inti the blood.
They accumulate in the lymphoid tissues such as lymph noides and the spleen waiting for pathogens to break into the body
When a B lymphocyte comes in contact with a specific antigen (An antigen is a substance, often a molecule or part of a cell, that triggers an immune response), it becomes activated (each B lymphocyte is triggered by a single specific antigen) (B lymphocytes can also be activated by helper T-cells).
Once triggered by an antigen, it begins to proliferate to form millions of clones.
These daughter cells then differentiate to become one of two types: plasma cells or memory B lymphocytes.
Plasma cells have the role of producing antibodies (antibodies are a y-shaped protein that bind to specific antigens - that is the specific antigen that triggered the b lymphocyte).
These antibodies are released into the bloodstream and migrate to the infected areas of the body.
The antibody has a shape that is compatible with the specific antigen which enables it to bind to it forming an 'antigen-antibody complex'.
The antibodies do not directly kill/destroy the antigen but instead interfere with the functioning of the pathogen by neutralisation (deactivating a pathogen or toxin by blocking its active site). This:
Blocks the pathogen from entering into cells, preventing it from infecting healthy cells (in regards to viruses).
Inhibits the pathogens ability to replicate and thus, limits the spread and growth within the host.
Marks pathogens for destruction by other immune cells such (opsonization) as macrophages.
Prevents pathogens from attaching to tissue/cells leaving them free-floating and vulnerable to being engulfed by phagocytes such as macrophages.
Prevents pathogens from causing damage such as releasing toxins or invading/destorying host cells (refer to first dot point).
Can trigger the activation of proteins/complement system (leading to a cascade reaction).
memory b lymphocyte
Memory B Lymphocytes provide immunological memory (a long-term defence against antigens), however remain dormant in the lymph tissue. If the organism/animal is exposed to the same antigen again, memory cells recognise it (hence 'memory') and divide to produce anti-body producing plasma cells. This allows for the immune response to an antigen that your body has already met before to be: - Faster - Stronger - Longer lasting (Symptoms should be less severe and last for a shorter amount of time - more efficient immune repsonse).
Cell-mediated immunity
Life Cycle of a T Lymphocyte:
Are Produced in the bone marrow and are then released into the blood and travel to the thymus gland where they mature.
Once the T cells are fully matured, they are released back into the blood where they circulate in an inactive state.
If a T lymphocyte come sinto contact with its specific antigen, the receptors on its surface allows it to bind to a specific antigen (e.g. antigen presenting macrophage) activating the cell.
Cytotoxic T Lymphocytes (aka Killer T Cells)
Serve to kill foreign, infected and abnormal cells (e.g. bacteria, fungi, viruses or cells infected with viruses or cancerous cells).
Cytotoxic T cells kill infected or cancerous cells by recognizing abnormal peptides/antigens displayed on the target cell's cell membrane via MHC class I molecules (these are used for endogeneous antigens such as viruses and cancers).
Once the T cell binds to the target, it releases perforin, which creates pores in the cell membrane, and granzymes (chemicals that break down the internal structures of the cell), which enter through the pores and trigger apoptosis (cell death). This process ensures that the infected or cancerous cell is destroyed without harming surrounding healthy tissue.
Helper T Lymphocytes
Help promote the activities of other immune repsonses
Helper T Lymphocytes recognise the antigen displayed on the MHC class II molceules (these are used for exogenous antigens such as bacteria and fungi) by antigen-presenting cells (APCs) such as dendricitc cells and macrophages (when they engulf/phagocytose the pathogen they present it on their plasma memebrane).
Once recognised the presented antigen, they secrete chemicals called cytokines which increase the activitiy of phagocytes, help promote inflammation, stimulate the production of Cytotocix T Lymphocytes, and stimulate B lymphocytes to differentiate to form plasma cells and Memory B Lymphocytes.
Suppressor T Lymphocytes
Are responsible for turning off the immune response after the antigen has been successfully contained, destroyed, or removed.
Memory T Lymphocytes
Provide the body with long term defence against antigens.
They persist after an infection, to enable a larger and faster response upon reinfection with the same pathogen.
More specifically, if the body is exposed to the same antigen, the memory T cells will recognise it and divides into cytotoxic and helper T lymphocytes.