Component 3: Immunology and Disease Flashcards
What does the innate immune system do?
reduces risk of infection of pathogens (prevents entry of pathogens)
Natural Barrier: Skin flora
Skin flora provides protection against pathogenic bacteria
- compromises of bacteria and fungi
- permanent residence, don’t cause disease
- outcompete pathogenic strains
- maintain low pH on the skin, preventing overgrowth of pathogens
Natural Barrier: Ciliated epithelial cells
Ciliated epithelial cells in the respiratory tract waft mucus (secreted by goblet cells that traps pathogens from inhaled air) to top of trachea, where it is swallowed into the stomach and stomach acid kills any microbes (very low pH)
Natural Barrier: tears, mucus and saliva
Tears, mucus and saliva all contain lysozymes, an enzyme that hydrolyses peptidoglycan in bacterial cell walls, killing the bacteria
Natural Barrier: Inflammation/Blood clotting
Blood clotting seals wounds and prevents entry of microbes (reducing infection)
- inflammation sets in: raising temperature so that’s unfavourable for microbe growth and increased blood flow to bring more phagocytic cells
Natural Barrier: Skin
The skin is made up of keratinised (epidermal cells) and collagen (connective tissue of dermis)
- vitamin C is essential for collagen biosynthesis, so skin is maintained by vitamin C = strong connective tissue
Natural Barrier: engulf and destroy
if microbes enter the blood phagocytes (including macrophages and neutrophils) ingest and destroy the invading microbes
Phagocytosis
- Pathogens entering the body are phagocytosed (enter a phagocyte by endocytosis)
- Lysosomes fuse with the vacuole containing the pathogen, releasing toxic compounds which destroy the ingested microbes - enzymes and hydrogen peroxide
- Debris is released and antigens from the microbes are presented on the surface of the macrophage in antigen presentation which stimulates lymphocytes
What are B lymphocytes?
B lymphocytes are produced by stem cells in bone marrow and mature in the spleen and lymph nodes, have specialised receptors on the plasma membrane
What does the humoral response result in?
This response results in the production of antibodies
What is the process of the humoral response?
- Antigen presentation causes B lymphocytes to respond with clonal selection taking place, every B lymphocyte has a unique shaped antigen receptor and whichever lymphocyte has a complementary receptor will bind to antigen, stimulating clonal expansion
- The complementary B lymphocyte then undergoes clonal expansion, induces cloning of specific B lymphocyte by mitosis:
· develops into plasma cells which produce antibodies with specific antigen receptors
· also produces memory cells, divide again if same antigen returns (dormant until then)
Antibodies definition
An immunoglobulin produced by the body’s immune system in response to antigens
Antibody molecule
- quaternary structure
- each molecule is made up of 4 polypeptides (2 light and 2 heavy)
- disulphide bonds
- variable portions are specific to each antigen
- each antibody molecule can bind to 2 antigen molecules
- constant region binds to phagocytes
- IgG in the most common (crosses placenta)
Antigens
- substances that are recognised as foreign by the immune system
- proteins, polysaccharide or glycoprotein molecules
- stimulate an immune response
- usually a specific shape
- can be on the cell surface of foreign tissue such as organ transplants and transfused blood cells
- each type of pathogen has its own unique antigens; these are genetically determined
- can be free molecules such as toxins released by microbes
- can be on the surface of bacteria or virus
What are the functions of antibodies?
Antibodies bind to microbes and “non-self cells”
- Opsonisation
- Agglutination
What is Opsonisation?
a process by which antibody molecules attached to the phagocyte makes an invading microbe more susceptible to phagocytosis
What is Agglutination?
the formation of clumps of cells as a result of the binding of specific antibodies to surface antigenic components
What does the cell-mediated response refer to?
The activation of phagocytic cells, B lymphocytes and T lymphocytes
What are T lymphocytes?
T lymphocytes are produced by stem cells in the bone marrow, migrate to the thymus to mature/be selected and develop into:
- T suppressor cells (Ts), switch off the immune system response
- T killer cells (Tk), which kill pathogenic cells with antigens by lysing them
- T helper cells (Th), activates antibody response, release chemicals including cytokines to activate macrophages, B lymphocytes and other T lymphocytes (important for a response)
Cytokines
- chemical messengers involved in activation of immune cells
- stimulate phagocytic cells, monocytes and neutrophils to engulf and digest pathogens
- stimulate B and T lymphocytes to undergo clonal expansion (these lymphocytes generate the cell-mediated response; B lymphocytes generate the humoral response)
- stimulate B lymphocytes to make antibodies
Cell-Mediated Response Process
- Phagocytes engulf microbes, destroy them and present their antigens
- Th cells which recognise these antigens activate B lymphocytes, other T lymphocytes and macrophages
- They do this by releasing molecules called cytokines and other chemical messengers
- These bind to the cell membrane and activate/de-activate cells
Primary Immune Response
- In first exposure to an antigen there is a latent period in which the invading pathogen is engulfed and destroyed by a phagocyte and the pathogens antigens being presented to the Th cells
- Th cells activate B cells, Tk cells and macrophages (B lymphocytes which have receptors complementary to the antigen are stimulated in clonal selection to divide many times in clonal expansion
- this means that there is a latent period where there is no response
- also means that the immune response is specific to that pathogen/antigen
- some of these cells differentiate into antibody producing cells (plasma cells) as well as memory cells (population of memory cells are produced)
- antibodies are produced which clear the infection within 2-3 weeks
Secondary immune response
- as the immune system has already encountered the pathogen before there are many memory cells present
- quicker (shorter latent period), produces more antibodies (10-100 times than initial response) and antibodies stay in the blood for longer (no symptoms develop as levels stay high)
- stimulated by much smaller quantities of antigen
- this is why we vaccinate people, it leads to a secondary response which is faster and means pathogens are destroyed before they can become established and cause symptoms
Definition: Pathogenic
an organism that causes damage to its host
Definition: Infectious
a disease that may be passed or transmitted from one individual to another
Definition: Carrier
a person who shows no symptoms when infected by a disease organism but can pass the disease on to another individual
Definition: Disease reservoir
where a pathogen is normally found; this may be in humans or another animal and may be a source of infection
Definition: endemic
a disease which is always present at low levels in an area
Definition: epidemic
where there is a significant increase in the usual number of cases of a disease often associated with rapid spread
Definition: pandemic
an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people
Definition: antibiotics
substances produced by microorganisms (fungus) which diminishes the growth of bacteria
Definition: antibiotic resistance
where a microorganism, which should be affected by an antibiotic, is no longer susceptible to it
Definition: vector
a living organism which transfers a disease from one individual to another
Definition: toxin
is a chemical produced by a microorganism which causes damage to its host
Definition: antigenic types
- organisms with the same or very similar antigens on the surface
- such types are sub groups or strains of a microbial species which may be used to trace infections
- they are usually identified by using antibodies from serum