Immune system Flashcards
Pathogen
A disease-causing agent – can be viruses, bacteria, fungi, protoctists (amoeba causes infection of the intestine), animals, plants (only to other plants), proteins (pollen makes the immune system overreact) – only in the kingdom of Archeans there are no recognized pathogens
Zoonosis – cause?
a disease that can be transmitted from an infected animal to a non-infected human. Some pathogens are species-specific but some can cross species barriers (changing their receptors to fit other cell glycoproteins) like rabies virus, SIV (HIV), tuberculosis, COVID-19…
Organs and tissues of the human immune system and their functions
- Bone marrow + thymus – development of immune system cells (T-ly in the thymus and B-ly in the bone marrow)
- Lymph nodes – position of the lymph nodes to prevent the pathogens from entering the trunk where vital organs are situated
(Palatine) tonsils – have to be taken out if the person is constantly sick as they can become a source of pathogens
Spleen
Appendix – storage of immune cells/tissue – impaired flow unlike in the rest of the long intestine, accumulation of pathogens
Lymphatic tissue along digestive, respiratory, and reproductive systems trap pathogens - Lymphatic vessels have dead ends
Types of the immune system and how do they act
When a bacteria gets in the body, innate and adaptive immunity are activated simultaneously and happen at the same time
1. Innate/non-specific
2. Adaptive/specific
Innate/nonspecific immune system mechanisms and steps
The immune-response is the same no matter the pathogen
1st line of defense are skin and mucus
2nd line of defense is phagocytes or phagocytic leukocytes
Describe the 1st line of defense of innate immunity
1st line of defense is skin and mucous – they are physical barriers to infection
Epidermis is 20-30 cells thick and acidic and dermis is 20-40x thicker, has blood vessels, hair, tissue-specific STEM cells that renew skin on a daily basis, and sebaceous glands that produce sebum (oily substance made of lactic and fatty acid) which is slightly acidic and thus prevents the growth of pathogens on the skin
The mucous membrane protects internal cavities that are exposed to the external environment, mucous glands (exocrine) produce mucus (mostly water) which contains lysozyme that destroys the bacterial cell wall (peptidoglycan)
Describe the 2nd line of defense of innate immunity
2nd line of defense are phagocytes or phagocytic leukocytes – they are cells in the interstitial space that recognize pathogens, perform phagocytosis (endocytosis) and immediately alarm the 3rd line of defense
Phagocytes are white blood cells, specifically neutrophils and monocytes (macrophages) – their purpose is to recognize a foreign pathogen by its antigen and engulf it by
once a pathogen is recognized, monocytes differentiate into macrophages and perform their function
endocytosis/phagocytosis – they move by amoebal movement (creates arms to swim) and lysosome inside fuses with the vessel containing the pathogen and destroy it
White blood cell types
neutrophils and monocytes (phagocytes)
eosinophil and basophil (play a role in allergic reactions)
lymphocytes (B-ly, T-ly)
What can molecules with a cell to cell recognition function be used for?
- Recognition and binding of a pathogen onto the surface protein of a host cell
- Recognition of foreign cells by the immune system and triggering of the immune response
Antigen
Intramembrane protein (glycoprotein)
the basis or distinction between self and non-self-cells because cells from different individuals have different AG while all cells of the same individual have the same AG
When a pathogen enters the body, AG is what the immune system reacts against
RBC groups system – antigens and antibodies
O group: AG H – anti-A, anti-B
A group: AG H and sugar – anti-B
B group: AG H and amine – anti-A
AB group: AG H, sugar and amine
Rh +: AG Rh
Rh +: / – anti-Rh
In plasma, there are antibodies against whichever AG is not found on an individual’s RBC. Because of this, 0-minus is the universal donor and AB-minus the universal receiver. People inherit the RBC groups but not the Rh types (antigen developed only if they get in contact with Rh+ and already have genetic potential for it)
Antibodies (AB) function and structure
Immunoglobulins (Ig) are proteins that recognize and bind to specific AG
They are mobile and soluble unlike antigen receptors and are specific to one pathogen
They are released y B-lymphocytes all over the body and attach themselves to AG on a pathogen
Made out of 4 polypeptide chains joined together (cystine, disulfide bridges) to form a Y-shaped structure with a constant and a variable region
The AG binding site is on the tips of variable regions (specific, unique a-a sequence) where AB-AG complexes are formed
How do antibodies destroy pathogens?
Three pathways:
1. Neutralization – blocks viral binding sites and coats bacteria (creating a membrane around them) – this prevents them from binding and thus replicating
2. Creates holes on the pathogen’s membrane
3. Agglutination of microbes – marks them for destruction by making them larger and less mobile, easier target for phagocytes – one AB binds to AG of two pathogens
Role of B-lymphocytes
Every lymphocyte has a membrane-bound molecule called AG receptor which can recognize only one specific AG so every human has millions of different types of lymphocytes
They produce antibodies – many different types of B-ly exist because each produces only a single type of AB and one type of AB can bind to only one specific AG
Majority of lymphocytes are situated outside of blood, in lymph and interstitial fluid
Explain the mechanisms of adaptive immunity
3rd line of defense mediated by T-ly and B-ly cells
1) Phagocytic leukocytes (macrophages) attach pathogen’s AG on its surface after phagocytosis by attaching it to its MHCH protein receptor (major human histocompatibility complex)
2) When AG attached to MHCH it turns the phagocyte into an antigen-presenting cell (APC)
3) T-helper lymphocyte recognizes the pathogen’s AG on the surface of the leukocyte by binding to it with their AG receptors – macrophage sends a signal which activates it
4) Activated T-helper activates the specific B-lymphocyte to confirm the AG’s presence because B-ly have receptor in their membrane that is complementary to the AG
5) If it fits, B-ly are activated by cytokines from the T-helper cell
6) The activated B-ly divide by mitosis and produce two types of cells (proliferation process): plasma and memory which fight infection in different ways
Plasma vs memory cells
Both produced by B-lymphocytes
Enlarged B-cell clones with an extensive rER to fulfill their function and produce AB in order to fight the infection
Memory cells stay the same and wait for another infection when they immediately react and directly produce more B-cells and AB, without T-cells. The stronger the infection, the stronger the developed immunity (more memory cells) and they either last for a few years or forever
Primary and secondary immune response
Primary exposure = first infection, secondary exposure = every other time of infection
If a pathogen invades a body a 2nd time, a much faster and more intense immune response will occur because a large number of memory cells has remained after the 1st infection and they are capable of producing large amounts of AB very quickly when stimulated by an AG
The properties of the secondary IR are the reason why vaccinations against some AG needs multiple (booster) shots
Polyclonal vs monoclonal antibodies
Most microbes have more than one AG on their surface so they stimulate more than one type of lymphocytes and result in the production of many different AB. This happens any time we’re infected in a natural way
Monoclonal AB are only possible by vaccination, they are the basis for tests (diagnosis of COVID, pregnancy) and sometimes for treatment (tetanus, venomous bite)
Explain how a pregnancy test kit works
based on detecting the human chorionic gonadotropin (hCG) which is a hormone of early pregnancy in urine (peaks 2 weeks after conception, cause of the morning sickness symptoms) – three types of monoclonal AB are needed
1. hCG joins with specific monoclonal AB inside the kit
2. AB-hCG complex joins with immobilized monoclonal AB causing the color of the new complex to change in the first window
3. The second window contains a third type of monoclonal AB which joins with an “empty” AB specific for hCG – exists to ensure that the test and receptors work
What is vaccination
Also called immunization, it acts as the 1st exposure to a pathogen (AG) and triggers the primary immune response. The AG produced as a result stimulate clonal selection and the development of immune memory (Bm) but without developing the disease symptoms
They may contain dead pathogens, weakened (attenuated) pathogens, AG only (in traditional vaccines) or DNA/mRNA coding for a pathogen’s AG (in advanced vaccines like COVID-19, body cells produce the AG) – have to have significantly reduced pathogenicity
It can be injected (intramuscular, subcutaneous) or swallowed
Benefits and risks of vaccines
Complete eradication of diseases (smallpox), reduced death rate and long-term disabilities (blindness form rubella), reduced health-care costs and herd immunity
Reduced effectiveness of the immune system due to extensive vaccination, vaccine immunity sometimes less effective than natural immunity
Smallpox
the most devastating disease known, viral, 3/10 all cases died, eradicated, the last case reported in 1977
Herd immunity
indirect protection from an infectious disease when a significant proportion of the population has contracted a disease or been vaccinated so disease spread is impeded
percentage of population that has to be vaccinated to achieve herd immunity is estimated by formula (1 – 1/R) * 100% where R is the average number of people that an infected person infects (depends on the disease)
Antibiotics – where are they found in nature?
antimicrobial (mostly antibacterial) chemicals that kill bacteria by impeding their DNA/protein/cell wall (e.g. penicillin) synthesis. They are prescribed to treat bacterial infections but are ineffective against viruses and eukaryotic cells
saprotrophic fungi make them to kill saprotrophic bacteria with which they compete for dead organic matter
What is antibiotic resistance?
It happens when resistant strains are not killed by the antibiotic so they multiply and spread (natural selection)
Only multiple resistance is problematic (e.g. MRSA) – evolution of multiple antibiotic resistance happens rapidly because they can pass genes from one species to another and ARGs (antibiotic-resistance genes) remain in pathogenic bacteria if antibiotic is no longer used
How can we avoid increasing antibiotic resistance?
by prescribing antibiotics only for serious bacterial infections for minimum time, hospital staff maintains high standards of hygiene to prevent cross-infection, farmers avoid use of antibiotics in animal food, pharmaceutical companies develop new classes of antibiotics (none have been introduced since 1980s)
explain the mechanisms of blood clotting is triggered
when a blood vessel is cut and blood flows out of it:
a) Platelets and damaged tissue cells release clotting factors (proteins) into the plasma at the site of the wound
b) Clotting factors activate the inactive form of enzyme prothrombin into its active form thrombin
c) Thrombin turns the soluble plasma protein fibrinogen into its fibrous form fibrin (insoluble) and fibrin molecules bind together to form a mesh of fibers across the wound
d) Blood cells are caught in the mash and form a clot, preventing further bleeding and entry of pathogens
AIDS – explain the name/symptoms and how it is caused
acquired immunodeficiency syndrome (acquired relates to the infectious nature of AIDS through HIV transmission, immunodeficient because it destroys a person’s specific immunity, and syndrome because there is large variation in the way the disease manifests itself (two AIDS patients can be affected by different sets of diseases)
The cause of AIDS is HIV (human immunodeficiency virus) – a retrovirus that infects T-helper lymphocytes and disables AB production – transmitted in contact with the body fluids of an infected person (blood, semen, vaginal mucus, through the placenta)
