Immunology Flashcards
(33 cards)
Immunology
The study of the immune system - an important part of the body’s response to infection.
‘Immunology is the study of the immune system and is a very important branch of the medical and biological sciences. The immune system protects us from infection through various lines of defence. If the
immune system is not functioning as it should, it can result in disease, such as autoimmunity, allergy and
cancer.’
The Nature of Infection
Infection describes when an organism replicates inside the body, resulting in disease.
Infection can occur within cells (e.g. viruses), whilst some replicate in organs (e.g. the gut)
Causative Agents of Infection (and Examples of Resulting Diseases)
Pathogen Definition:
‘Any small organism, such as a virus or a bacterium that can cause disease’.
Pathogens: Bacteria, Viruses, Fungi, Prions, Protoctists and Parasites
Bacteria
Bacteria are prokaryotes and often causes illness due to the toxins they produce as a result of their metabolism. Bacterial infections are treated by antibiotics, but bacteria are becoming increasingly resistant to antibiotics.
Examples:
• Chlamydia
• Gonorrhoea
• Tuberculosis
Viruses
Viruses are akaryotes because they are not proper cells. Many treatments that work against cellular pathogens will not work with viruses. Antibiotics are not effective against viral infections. SARS-CoV-2, the coronavirus that causes COVID-19, has recently become the best known virus.
Examples:
• Common Cold
• Mumps
• Measles
Fungi
Fungal infections can be from unicellular fungi (e.g. yeast) or multicellular fungi. Other fungal skin infections include toenail fungus and athlete’s foot. Fungal infections are known as mycoses in medicine.
Example:
• Yeast Infection (Thrush)
Prions
Prions are non-living pathogenic proteins which can act as an infectious organism. The mutant form of a prion protein, when ingested, can cause normal prion proteins to change shape. This causes damage to the nervous system and eventual death.
Example:
• Creudtzfeldt-Jakob disease (CJD)
Protoctists
Protoctists are eukaryotes and usually unicellular (but some simple multicellular forms exist). Examples include protozoa, algae and slime moulds. Some varieties causes diseases.
Example:
• Malaria
Don’t confuse the pathogen (Plasmodium) with the Anopheles mosquito that transmits the pathogen
Parasites
Parasites are organisms which live off another organism either external (ectoparasites) or internal (endoparasites). They can be multicellular (e.g. nematode worms which infect the digestive system). They can also include protozoa (e.g. causing toxoplasmosis).
Example:
• Toxoplasmosis
Toxoplasmosis is caused by Toxoplasma gondii, a parasitic protoctist. Many multicellular parasites can also cause infections, particularly in developing countries
Glossary terms in the innate immune system
• Self/Non self
• Major Histocompatibility complex/ Human leukocyte antigen (MHC/HLA)
• Antigen
• Inflammation
• Mast Cells
• Histamine, Cytokines
• Vascular permeability
• T regulatory cells (Tregs)
• Phagocytosis
• Macrophages and Neutrophils and dendritic cells
• Phagolysosome
• Antigen Presenting Cells (APC)
The immune system
Our bodies are really well prepared to prevent pathogens from gaining entry – this is non specific immunity.
Non specific immunity includes:
• Skin – a barrier to penetration
• Stomach acid – ‘disinfects’ food through destruction of pathogens
• Mucus – to prevent pathogens from attaching to cells
• Phagocytosis – white blood cells that engulf and destroys pathogens
• Fever – creates conditions that are not favourable for growth
• Inflammation – brings white blood cells to the site of injury or infection
• Lysozyme- antimicrobial enzyme found in tears, salvia, human milk and mucus
• Complement system – proteins in the blood that to alert your immune system
How do we know what is foreign in the body?
• Our bodies do have a mechanism that allows them to recognise our own cells and molecules (self) and foreign matter (non self)
• Each cell in our body has specific proteins on its surface that show the immune system that they belong in our bodies - Human leukocyte antigens (HLA) – also known as the Major Histocompatibility Complex – MHC).
• Your HLAs are genetically determined and are unique to each individual - they are coded for on chromosome 6 (224 genes) so we can recognise self or non self material and respond
HLA genes in practice – transplantation
• The HLA genes determine an individual’s tissue type, which varies from person to person as HLA genes have many possible variants.
• If you require a transplantation, tests are carried out to try and get a perfect match, or as close as possible match, between the HLA genes of the donor and those of the recipient to reduce the risk of the
transplanted organ being rejected.
• Individual HLA genes are inherited from your parents. Variants in the HLA genes are associated with more than 100 diseases, including infectious diseases like HIV, and some cancers.
• Some autoimmune conditions, including diabetes and multiple sclerosis, are also linked to specific variations in the HLA
The basics of immunity
• The function of the immune system to allow the body to recognise the difference between self and non self material.
• Any molecule that the body is able to identify as non self is known as an antigen.
• Antigens stimulate an immune response
• *In autoimmune conditions the body mistakenly recognises self material as an antigen so produces an immune response as well
Inflammation and immunity
• One of the first responses to an injury is inflammation. The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause.
1.) Mast cells secrete histamine that is a cell signalling compound that causes other cells to react
2.)Histamine increases blood flow in capillaries and causes them to become permeable (vascular permeability) so fluid (causing swelling) and leukocytes leave the capillary and go to the site of injury
3.) Histamine causes cells to release other chemicals such as cytokines which stimulate the immune system and promote phagocytosis and other immune responses
4.) T regulatory cells stop the immune response when it is no longer needed which removes these symptoms so the swelling, redness and temperature decreases at the site of injury (negative feedback loop).
Types of cells
Types of leukocytes can carry out phagocytosis and secrete chemicals that increase immune activity;
• Neutrophils – Short lived - destroy pathogens completely then die (pus)
• Macrophages – long lived - display the antigens of the pathogen on the surface on the MHC – this is known as an antigen producing cell
• Dendritic cells – ingested material is taken to lymph nodes and then display the antigens of the pathogen on the surface on the MHC – this is known as an antigen producing cell
Phagocytosis – phagocytes and macrophages
• If the physical or chemical barrier to infection in breached then the white blood cells are next in line.
There are two types – phagocytes and lymphocytes.
- Phagocytes track the pathogen through attractants such as chemicals or dead/damaged cells –
chemotaxis - Phagocytes have receptors on their surface that attach to the pathogen
- Phagocytes then ingest (through endocytosis) forming a phagosome inside the cell, this merges with a
lysosome creating a phagolysosome containing lysozymes that hydrolyse the pathogens cells wall and
destroy the pathogen. - The soluble products and dissolved in the cytoplasm of the phagocyte and any digestion products are expelled from the cell through exocytosis.
- In some phagocytes – macrophages - the MHC is then presented on the surface of the phagocyte.
These cells are known as antigen presenting cells. (APC)
Extra knowledge
• Pathogens that invade the body may be engulfed by cells that carry out Phagocytosis. One types of cell that can do this is the Macrophages The pathogen is engulfed through the process of endocytosis and forms a vesicle called a phagosome.
• The vesicle called the phagosome the merges with another vesicle called the lysosome, forming a new vesicle called a harose the pathose destroy cel that arme then neutrophils then die and form puss.
• However, macrophages don’t destroy the pathogen completely they present the antigen on its surface in a structure called the Major Histocompatibility complex which then triggers other parts of the immune system.
Key terms in the specific immune system
• Lymphocytes
• T cells – two main types: T helper (TH), T cytotoxic/killer (TC/K)
• T cell receptors (TCR)
• Activated TH cell
• Cell mediated immunity
• B cells – two main types: Plasma cells, memory cells
• B cell receptors (BCR)
• Activated B cell
• Humoral immunity
• Antibody
• Perforin
• immunoglobulins
Specific immunity
• There are two types of lymphocyte involved in specific response.
T Cells:
• These mature in the Thymus gland and are associated with cell mediated immunity which involved body cells.
• The two main types are T Helper (TH) and T cytotoxic/killer cells (TC/K).
• T helper cells have CD4 receptors
• T cytotoxic cells have CD8 receptors
• Their role is also to reactivate B cells after activation by a specific pathogen in the past
B cells:
• These mature in the bone marrow and are associated with humoral immunity (antibodies that are present in body fluids or plasma).
• The majority form clones of plasma cells that secrete antibodies into the into the blood but some form memory cells that provide the secondary immune response
Humoral immunity – B cells
• This type of immunity involves antibodies and as they are soluble in water they travel in the humours (fluids of the body) – lymph and blood plasma.
• B cells with the appropriate antibodies for many pathogens are present from birth (or through exposure – naturally through infection or artificial through vaccination
• B cells are specific to each antigen and it can take a long time to match the right antibody to the pathogen (like a jigsaw) so it is not as quick as cell mediated immunity which is turn is not as quick as inflammation and phagocytosis
B cell action
• Just like T cells, B cells can also be activated but by bonding to antigens that have not been processed.
• However they can only bond with antigens that they have a specific receptor for.
• This is different to T cells who need the antigen processed by an APC first.
• Once activated they have create memory cells and plasma cells
Following B cell activation
The B Cell clones then develop into one of two types of cell:
Plasma cells:
• These cells secrete antibodies into the blood plasma which lead to the destruction of the antigen in different ways. These cells produce thousands of antibodies a second but only live for a few days. This is the primary immune response.
Memory cells:
• Some of the B cells (just like T cells) become memory cells that do not produce antibodies but continue to stay in the body for decades. When they are activated they rapidly produce plasma cells and more memory cells and this provides the secondary immune response
Cell-mediated immune response
- Pathogens are engulfed and hydrolysed by a Macrophage and present the pathogens MHC on its surface.
- CD4 or CD8 Receptors on a specific T Cells bind to the macrophage presenting the antigens
- This attachment activates the T cells to divide rapidly by mitosis and form a clone of genetically identical cells. The cytokines are proteins that activate other T cells
- The cloned T cells then:
- Can become a memory cell ready to combat the specific pathogen again with the matching CD4 receptor.
- Stimulates B cells to divide and secrete their antibodies.
- Stimulates phagocytosis by further phagocytes.
- Activates cytotoxic T cells (TC cells) or killer T cells (TK cells) that produce a protein called perforin that makes holes in the cell membrane so destroys infected cells
