U4 AOS1 Biology Revision Set

VCE Unit 3/4 Biology

Antigens

unique molecules or parts of molecules that can be recognised by receptors on T cells or by antibodies produced by B cells. They allow the body to recognise potentially harmful pathogens and mount an immune response against them

Immunogens

antigens that elicit an immune response

Allergens

antigens that result in an immediate hypersensitivity reaction, an overreaction of the immune system to antigens that would otherwise be harmless

Self-antigens

antigens expressed by the bodies own cells

Non-self antigens

antigens that are not expressed by the bodies own cells

Receptors on B lymphocytes

membrane-bound antibodies that recognise free antigens or antigens on the surface of a pathogen

Receptors on T lymphocytes

recognise antigens presented by an organism’s own antigen-presenting cells

antigen-presenting cells (APCs)

cells which have antigens on their surface membranes

Major histocompatibility complex (MHC)

proteins on the surface of a bodies cells which present self or non-self antigens to T cells.

positive selection

The first stage of the maturation of T lymphocytes which occurs in the thymus. This involves checking if the cells can bind to MHCs, and if not are destroyed through apoptosis

negative selection

The second stage of the maturation of T-lymphocytes, in which T cells that react with self-antigens in the thymus bind tightly to the cells in the thymus and eventually die.

clonal deletion

The 2-step process of T lymphocyte maturation, consisting of positive and negative selection (in that order)

self-tolerance

the inability to respond to self-antigens. If this breaks down and the immune system responds to self-aantigens, it results in autoimmune disease

Pathogens

agents that cause disease, can be primary or opportunistic and cellular or non-cellular

Primary pathogens

cause any disease at any time they are present

Opportunistic pathogens

only cause disease when the host’s defenses have been weakened.

Cellular pathogens

bacteria, fungi, oomycetes, protozoans, worms and anthropods.

oomycetes

cellular pathogens that include organisms that cause blight and mildew in plants and life-threatening infections in animals

Protozoans

unicellular eukaryotes (cellular pathogen). Express different antigens on their surface, which change throughout their life-span through antigenetic variation, allowing them to evade immune detection

antigenetic variation

the process by which a cell’s surface antigens can change

Anthropods

invertebrates with exoskeletons, whose saliva can trigger an immune response and inhibit inflammation - a cellular pathogen.

Non-cellular pathogens

non-living pathogens that still have the ability to cause disease, includes viruses, viroids and prions

Virus

an infection agent that is composed of genetiv material (DNA or RNA) enclosed in a protein coat, some with a capsid as well. They can undergo antigenetic drift and shift

Capsid

a lipoprotein envelope on some viruses

Antigenetic drift

the process by which viruses undergo maturation during replication, creating new and similar viruses

antigenetic shift

an abrupt change in genetic code of a virus due to a reassortment of genes from different viral strains, resulting in significantly different antigens on the coat of the virus. The abrupt genetic changes can result in a virus with different characteristics, allowing it to infect new hosts.

Types of immune system barries

• Physical

• Chemical

• Microbiological

Innate immune response

the immediate action of the immune system which can be highly destructive and is not specific, having no memory of the infection. Includes the action of phagocytes, inflammatory cells, natural killer cells, dendritic cells and complement proteins. Can also refer to the physical, chemical and microbiological barriers to infection.

phagocytes

leukocytes that are able to engulf and break down pathogens in a process known as phagocytosis. These include neutrophils, macrophages, monocytes and dendritic cells

Adaptive immune response

the slower immune response which is highly specific to a particular antigen, including the humoral and cell-mediated responses. This can include all B cells in humoral immunity and all T cells in cell mediated

Stages of an immune response

• Keep pathogens out, using chemical and physical barriers

• Pathogens get in. Innate immune response is activated, possibly initiating the inflammatory response

• Pathogens are winning. APCs will communicate this from the innate to adaptive response, activating the more highly specified response, producing antigens and lymphocytes to fight the infection

antigen

a chemical compound that identifies a specific pathogen

lymphocytes

white blood cells, which have PRRs on their surface - these are produced by stem cells in bone marrow

Allergens

Antigens that are usually harmless and shouldn’t be fought but lead to an immune response due to an overreaction of the immune system

Immunity

acquiring a system to defend against pathogen infections. It can be long or short term and involves the action of anitbodies, B cells and T cells.

Lymphatic system

the bodily system involved with drainage and developing immunity and controlling pathogens. It is a subsystem of the circulatory and immune system

Lymph nodes

organs in the body which work in conjunction with the blood to exchange white blood cells and waste. contain macrophages and dendritic cells to swallow up pathogens to cleanse lymph

viroid

(non-cellular pathogen) pathogen of plants that competes for nucleotides in DNA sequences, acting like a tumour and inhibiting some cellular processes

Prion

(non-cellular pathogen) infectious agents that do not contain genetic material, They are proteins with an abnormal shape that cause neurodegenerative diseases in mammals without triggering an immune response.

Examples of physical barriers

skin or bark

Examples of chemical barriers

Alkaloids (toxic), cyanogenic glycosides, phenolics, saponins and terpenes (found in insecticides). also saliva and stomach acids, etc.

Cyanogenic glycosides

compounds that break down to form hydrogen cyanide, which blocks the ETC and therefore ATP production

Phenolics

molecules that disrupt cellular metabolism

PAMPs

pathogen-associated molecular patterns, which are recognised by PRRs as an immune response in plants.

Immune responses in plants

PAMPs being recognised by PRRs, switching on resistance genes.

PRRs

pattern recognition receptors, which recognise PAMPs as an immune response in plants

resistance genes

genes present in plants that code for R proteins, which switch on a plant’s defences when it recognises specific PAMPs.

Defensive proteins in plants

• defensins - act as digestive enzymes

• Protease inhibitors - inhibit important digestive enzymes

• Hydrolytic enzymes - break down cell walls

Granulocytes

leukocytes that contain many cytoplasmic granules, which are released during an immune response. These include neutrophils, basophils, eosinophils and mast cells

Phagocytosis

the process by which phagocytes engulf and break down pathogens

Anitbodies

recognises and is complementary to antigens

Types of antigens

• Allergens

• Immunogens

exotoxins

a soluble poisonous substance produced during growth of a microorganism and released into the surrounding medium.

endotoxins

a toxin present inside a bacterial cell that is released when it is destroyed.

ectoparasites

parasites that live on an organism

endoparasites

parasites that live in the organism

lytic cycle

a process of viral replication where a virus infects a host cell, replicates itself, and then destroys the host cell to release new viral particles

Inflammation

a non-specific response by the immune system which demobilises defensive cells, limits the spread of and kills pathogens and initiate tissue repair

cytokines

molecules released that attract additional immune cells to the site of infection

Stages of the inflammation response

1. pathogens enter through broken skin barrier, and damaged cells release cytokines

2. Platelets release blood-clotting factors to restore skin barrier

3. Mast cells release histamine to stimulate vasodilation, also releasing cytokines and increasing permeability of capillaries

4. Neutrophils phagocytose the pathogens

5. Eosinophils move into area and release more cytokines

6. Macrophages phagocytose pathogens and release cytokines

7. Dendritic cells, macrophages and neutrophils phagocytose pathogens before presenting them on their surface to T and B lymphocytes

Histamine

triggers allergic reactions and aids in immune responses, as well as stimulating vasodilation and increased blood vessel permeability in the infammatory response

vasodilation

the dilatation of blood vessels, which decreases blood pressure.

Neutrophils

one of the first cells to arrive at the site of an infection in the inflammatory response

Macrophages

phagocytose pathogens and release cytokines

Mast cells

a type of white blood cell which are released from bone marrow and act as guarding cells. They are stimulated to release histamines and cytokines

Neutrophil

like a standard police officer, quick to respond but not specialised so die rapidly. they phagocytosing bacteria, are found in the bloodstream and are attracted to tissue cytokines.

Eosinphil

like a fumigator, more specialised and releases chemicals. travel to specific tissue and can cause tissue damage

Basophil

the leukocyte involved when a region is inflammed like firefighter

Macrophage

like riot police - slower to respond but better prepared and survive for longer. They engulf large cells, identify unwanted particles or foreign cells and are involved in phagocytosis

Dendritic cells

like signalman - identifies the pathogen and sends signals to the appropriate special forces (lymphocytes). In charge of phagocytosing pathogens in local area before to lymph nodes to be presented to B and T cells. It maintains communication with other immune cells through cytokines

Natural Killer (NK) cells

search for self-markers that confirm whether a cell is foreign or self. They kill cells infected with viruses or abnormally functioning cells such as cancer

Complement proteins

proteins in the plasma of the blood. They easily move out of blood vessels made permeable by histamine, acting as chemoattractants

chemoattractants

cells that attract leukocytes

Interfons

interfere with replication of several viruses. They activate immune cells, such as macrophages, attracting to area of infection

Major histocompatibility complex (MHC) proteins

located on the surface of cells, which present self-antigens or non-self antigens to T lymphocytes. They have classes (including I and II, which are both involved in antigen presentation.

Antigen presentation

refers to the arrangement of specific antigens on a cells surface , allowing immune cells to cells to recognise self and non-self cells, linking innate and adaptive immunity

MHC-I

mostly found on all nucleated cells. NK cells kill cells that don’t present this protein

MHC-II

links innate and adaptive responses, activating helper t cells. can be expressed on all cells, conditionally. most are found on antigen presenting cells. They are responsible for presenting foreign antigens to T cells

primary lymphatic tissues

bone marrow and thymus - where lymphocytes mature

bone marrow

includes stem cells that produce white blood cells, which are important to the immune response

Thymus

the location in which T-lymphocytes can mature

secondary lymphoid organs and tissues

• appendix

• spleen

• tonsils

• lymph nodes

This is where B and T lymphocytes come into contact with pathogens

lymph nodes

located at key points in the body. They provide a place for memory cells to search for antigens.

spleen

controls the number of red blood cells and destroys old and defective cells. It stores a quarter of the body’s lymphocytes and is the site of B cell maturation and activation

Plasma cells

differentiate white blood cells and develop from B cells, making antibodies to fight bacteria and viruses

Lymph vessels

flow one-way due to valves, with lymph nodes acting as filters.

humoural immunity

a branch of the adaptive immune response concerning B cells which target exogenous antigens

cell-mediated immunity

a branch of the adaptive immune response concerning T cells which target endogenous antigens - does not result in antigen production

exogenous antigens

antigens coming from outside the body

endogenous antigens

antigens coming from within the body

B-lymphocytes

a type of white blood cell that plays a crucial role in the adaptive immune system, specifically in humoral immunity.

T-lymphocytes

a type of white blood cell that plays a crucial role in the adaptive immune system, specifically in cell-mediated immunity.

Clonal proliferation/expansion

the process of differentiation which allows B cells to become plasma or memory cells

clonal selection

refers to how one specific antigen will only activate a lymphocyte with a receptor that specifically recognises that antigen

antibodies

Y-shaped proteins produced by the immune system to identify and neutralize foreign substances like bacteria and viruses.

antibody functions

• neutralisation

• agglutination

• precipitation

neutralisation (antibody function)

antibodies bind to bacterial toxins on the surface of pathogens, preventing entry into host cells

Agglutination (antibody function)

antigens bind to antibodies to form antigen-antibody complexes, which activate phagocytes

precipitation (antibody function)

antibodies bind to soluble antigens, making them insoluble and forcing them out of a solution as a precipitate.

Immunological memory

the ability for the immune system to remember pathogens and how they are dealt with