Chalter 12 Specific Resistance To Infection Flashcards
What are lymphocytes?
Lymphocytes are cells that are involved in both non-specific and specific defence.
Describe lymphocytes in the body.
- About 20-30% of the white cells in the blood are lymphocytes.
- However, these circulating lymphocytes are only a small fraction of the total lymphocytes in the body.
- The combined weight of lymphocytes in a person’s body is over a kilogram.
Where are lymphocytes produced?
- Most lymphocytes are produced in the bone marrow, but they are also produced in lymphoid tissues.
- Lymphocytes roam throughout the body.
- They are able to wander through a tissue and then enter the blood, or the lymph, to be transported to another part of the body where they again enter the tissues.
What are Pathogens/ pathogenic organisms?
Micro-organisms which can cause diseases.
What are Macrophages?
- They are also involved in both non-specific and specific defence.
- They are large phagocytic cells that develop from a type of white blood cell.
- They are able to consume foreign substances and micro-organisms by phagocytosis.
- They are involved in specific defence by alerting the immune system to the presence of foreign material.
What are specific defences?
- Specific defences are those directed towards a particular pathogen.
- They are apart of our immune system.
Give an example of a specific defence.
- If you get infected (or vaccinated) with chickenpox virus, the body will make antibodies to combat that virus.
- Those antibodies are only effective against chickenpox virus and will not work against any other virus or bacterium.
What is the immune system composed of ?
- Different types of cells that occur in most of the organs of the body.
- These cells protect against foreign organisms, a range of alien chemicals, as well as cancerous and other abnormal cells.
- Some of these cells are non-specific, such as phagocytes, which are able to engulf and digest micro-organisms and cell debris.
- However, others such as B cells and T cells only provide protection against a specific micro-organisms or disease-causing substance.
- When these cells react is it called the Immune System.
What is Immune response ?
- It is a homeostatic mechanism.
- When micro-organisms or foreign substances enter the body, the immune response helps to deal with the invasion and restore the internal environment to its normal condition.
What are the 2 parts of the immune response?
- Humoral Response or Antibody-mediated immunity.
2. Cell-mediated response.
What is the function of the Humoral Response?
It involves the production of special proteins called antibodies, which circulate around the body and attack invading agents.
What is the function of the Cell-mediated response?
It involves formation of special lymphocytes that destroy invading agents.
What is the Lymphoid tissue?
- It is involved in both the humoral and cell-mediated responses.
- Most lymphoid tissue is in the lymph nodes but it also occurs in other parts of the body, such as the spleen, the thymus gland and the tonsils.
- Composed of two types of lymphocytes that are involved in the immune response - the B cells and T cells.
What does the B and T cells do?
B cells: Provide antibody-mediated immunity
T cells: Provide cell-mediated immunity.
Where do the B and T cells come from ?
-Both these cells are produced in the bone marrow, and both end up in the lymphoid tissue, but they mature by following two different routes between bone marrow and lymphoid tissue.
Where do the B and T cells end up?
- About half the cells produced by the bone marrow go to the thymus where they mature into T cells before being incorporated into the lymphoid tissues.
- The other half of the cells mature in the bone marrow to become B cells and then also become part of the lymphoid tissues.
How to remember B and T cells?
T cells: They mature in the Thymus
B cells: They mature in the Bone marrow
What is an Antigen?
- It is any substance capable of causing a specific immune response.
- Antigens are large molecules.
- They have many proteins, carbohydrates, lipids or nucleic acid.
- An antigen could be a virus particle or a whole micro-organism, such as a bacterial cell, or part of a bacterium, such as the flagella, cell wall or capsule.
- Toxins produced by bacteria are also antigens.
- Antigens are not necessarily associated with micro-organisms.
- Tissues transplanted from another person, blood cells or a foreign blood group, and such things as pollen grains and egg white contain antigens.
What is the role of Antigens?
- It Triggers Antibody-mediated and cell-mediated immunity.
- Such a substance, introduced to the body, causes the body to produce specific antibodies.
What are Self Antigens and Non-Self Antigens?
- Self Antigens - They are large molecules in a person’s own body which do not cause and immune response.
- Non-Self Antigens - Foreign compounds that do trigger an immune response.
- > The immune system becomes programmed to distinguish between self-antigens and non-self antigens before birth. From then on, it only attacks non-self antigens.
What is an antibody?
-It is a specialised protein that is produced in response to a non-self-antigen.
What are Immunoglobulins?
- Group of proteins in which the antibodies belong to, often represented as Ig.
- There are 5 classes of these antibodies, which vary in their structure and are designated IgA, IgD, IgE, IgG and IgM.
Why are the active sites on the antibody and antigen molecules said apply the Lock and Key analogy?
- The antibody produced in response to an antigen can combine with that antigen to form an antigen-antibody complex.
- Antigen molecules have specific active sites and at these sites the antibody can combine with the antigen.
- Each antibody can combine with only ONE particular antigen, in the same way that a key will only open a particular lock.
What is Antibody-mediated immunity?
- It is the humoral response which involves the production and release of antibodies into the blood and lymph.
- It provides resistance to viruses, bacteria and bacterial toxins before these micro-organisms or substances enter the body’s cells.
Where do clones come from ?
- Lymphoid tissue contains thousands of different types of B cells.
- Each type is capable of responding to a specific antigen.
- When an antigen activates B cells, they enlarge and divide into a group of cells called a clone.
What are Plasma cells?
Most of the clone become plasma cells, which secrete the specific antibody capable of attaching to the active site of the antigen.
What is the role of the antibodies secreted by the plasma cells?
These antibodies circulate in the blood, lymph and extracellular fluid to reach the site of the invasion of micro-organisms or foreign material.
What happens to the B cells of the clone that did not differentiate into plasma cells?
They remain as memory cells.
What do memory cells do?
They spread to all the body tissues to allow the response to occur more rapidly should the antigen enter the body again.
What is Primary Response?
-It is the immune reaction when it is first exposed to an antigen.
Explain how a Primary Response occurs.
- The body’s immune system usually responds fairly slowly, often taking several days to build up large amounts of antibodies.
- It takes times for the B cells to multiply and differentiate into plasma cells.
- As the plasma cells begin to decline.
- However, the primary response leaves the immune system with a memory of that particular antigen.
What is a Secondary Response?
It is a much faster response to the same antigen when it is exposed the second time because of the activity of the memory cells.
Explain how a Secondary Response occurs ?
- Plasma cells are able to form very quickly, with antibody levels in the blood plasma rising rapidly.
- Frequently, this response is so quick that the antigen has little opportunity to exert any noticeable effect on the body and no illness results.
How do antibodies work to provide resistance to infection?
All antibodies combine with the antigen for which they are specific to form an antigen-antibody complex.
List the possible things that the Antibodies may do.
- Combine with foreign enzymes or bacterial toxins, or inactivate them by inhibiting reaction with other cells or compounds.
- Bind to the surface of viruses and prevent the viruses from entering cells.
- Coat bacteria so that the bacteria are more easily consumed by phagocytes.
- Cause particles such as bacteria, viruses or foreign blood cells to clump together - a process known as agglutination.
- Dissolve organisms.
- React with soluble substances to make them insoluble and thus more easily consumed by phagocytes.
What is the function of Cell-mediated immunity?
- It provides resistance to the intracellular phase of bacterial and viral infections.
- It is also important in providing resistance to fungi and parasites, and is involved in the rejection of transplants of foreign tissue.
- It also appears to be important to fighting cancer cells.
What does the pathogens (such as bacteria responsible for tuberculosis and legionnaire’s disease) do?
They specialise in invading and replicating inside their hosts’ own cells, making them particularly difficult to overcome.
What are T lymphocytes?
- They are responsible for cellular immunity.
- They occur in the same lymphoid tissue as the B cells but occupy different areas of the tissue.
- Like the B cells, there are thousands of different types of T cells, and each type responds only to one particular antigen.
