Responding to antigens

Question 1

Innate immune response

Answer 1

An inborn system that lacks specificity and memory
Stimulates - inflammation and phagocytosis → both can occur quickly, even if the host has never been previously exposed to a particular pathogen.

Question 2

Inflammatory response

Answer 2

Reaction to an infection, injury, damaged tissue- results in:
Heat - due to increased blood flow
Pain - due to systemic response (ie fever), the stimulation of nerve endings through the release of histamine and swelling putting pressure on pain receptors.
Swelling - due to movement of fluid into tissues after vasodilation
Redness - due to vasodilation of blood vessels, leading to red blood cells released into tissue.
Due to accumulation of fluids and proteins and an increased blood supply to the infected region.

Question 3

Stages of inflammatory response

Answer 3

1. Initiation - involves the release of cytokines from damaged cells which trigger mast cells to undergo degranulation (release histamine)
2. Vasodilation - Histamine from mast cells promotes vasodilation and blood vessel permeability allowing neutrophils and other immune cells travel to the site of infection (also stimulated by cytokines)
3. Migration - phagocytes and complement proteins travel around the body and move from the permeable vessel to the infected site. They remove indigestible material.
   → Resolution includes a reversal of all the processes that produced the acute inflammation

Question 4

Monocytes

Answer 4

• found in tissue
• Undergo differentiation into macrophages or dendritic cell

Question 5

Neutrophils

Answer 5

• found in blood
• Most abundant circulating white blood cells
• Usually the first to site of infection
• Undergo phagocytosis
• Short life span

Question 6

Dendritic cells

Answer 6

• found in tissue
• Antigen presenting cells
• Undergo phagocytosis (presenting their antigens to T cells to activate the adaptive immune response)
• Have branched projections, providing them with a large SA:V improving their phagocytic and antigen presenting properties.

Question 7

Eosinophils

Answer 7

• found in blood
• Defend against larger parasitic agents (too large to be attacked by phagocytosis)
• Undergo degranulation (release of histamines)
• Undergo phagocytosis

Question 8

Natural killer cells

Answer 8

• Found in blood
• Once pathogens have gained entry into the body cells and become intracellular, they cannot be directly attacked by innate immune cells → are eliminated by NK cells
• Eliminate virus, infected cells and cancer cells by degranulation and induce apoptosis

Question 9

Mast cells

Answer 9

• found in tissue
• Mediate inflammatory response
• Upon stimulation, they release histamines, cytokines and heparin through degranulation

Question 10

Macrophages

Answer 10

• found in tissue
• Undergo phagocytosis
• Initiate acute inflammatory responses through secretion of various cytokines
• Antigen-presenting cells
• Recruit other immune cells to an infection site

Question 11

Degranulation

Answer 11

Process where immune cells release various toxic chemicals stored within secretory vesicles (cytoplasmic granules)
Natural killer cell degradation - releases proteases and perforin proteins, which insert holes in plasma membrane of foreign cells and induce apoptosis (programmed cell death)

Question 12

Phagocytosis

Answer 12

1. The pathogen is identified by a pattern recognition receptor (PRR)
2. Engulfment - ATP required to carry out endocytosis
3. Digestion - pathogen is engulfed in a vesicle called a phagosome. This fuses with a lysosome (forming a phagolysosome) and digestion of pathogen occurs using lysosomes
4. Secretion - undigested material is secreted using exocytosis
5. In macrophages and dendritic cells, some of this material is presented on MHC-II markers to activate the adaptive immune system

Question 13

Cytokines

Answer 13

Cytokines are a broad group of molecules which facilitate communication between immune cells and attracts other immune cells to help destroy the pathogen

Question 14

Histamine

Answer 14

Histamine is a type of cytokine that increases vascular permeability of blood vessels in inflamed areas making it easier for neutrophils, macrophages and blood proteins to squeeze out and into infected tissue

Question 15

Complement proteins

Answer 15

Complement = proteins that are dissolved in the plasma of one’s blood - they complement or add to the function of immune cells.
1. Process of chemotaxis which attracting phagocytes to the area (for inflammatory response)
2. They opsonization pathogens, marking them for destruction by phagocytes (specific proteins will attach to bacterias and mark for destruction)
3. They destroy pathogens by lysis (causing the bacterial cell membrane to rupture) through the initiation of the membrane-attack complex (MAC) (punches holes in bacteria and lets fluid inside the cytoplasm of bacteria out and kills it)

Question 16

Interferons

Answer 16

Increase the resistance of of uninfected cells to viral cells
When a cell is infected by a virus, the virus enters the cell and produces viral material. This signals the host cell to produce interferons, signalling molecules (cytokines). The virus infected cell will secrete interferons which attach to receptors on nearby cells and act as a warning signal so the cell can prepare for possible virus infection. The virus in the cell will replicate and when the host cell dies, the viral particles will be released

Question 17

Fever → second line defence

Answer 17

Following a cascade of events which results in a higher body temp to conserve heat, microbe reproduction in the body is slowed

Question 18

Physical barriers

Answer 18

Innate barriers that prevent the entry of pathogens into the body/ plant

Question 19

Blood clotting → part of second line of defence

Answer 19

• Platelets can ‘plug’ a wound area, producing serotonin to trigger blood vessels to constrict, minimising blood loss.
• Also produce thromboplastin to trigger a cascade of events to form a permanent clot.
• A protein chemical called FIBRIN is the key product made.

Question 20

Antigen

Answer 20

Any substance that triggers an immune response through the production of antibodies or immunoglobulins
Can be bacteria, virus, pollen, grains, chemicals, drugs, venom etc
- Self-antigens - antigens on cells are recognised by self-receptors as being part of the same body
Not foreign, usually tolerated by the immune system
- Non-self antigens - antigens that do not belong to the body’s own cells
Can be identified as invaders and can be attacked by the immune system.

Question 21

Antigen recognition depends on MHC markers

Answer 21

MHC-I is present on all nucleated cells of the body. Contains the binding site for an antigen. This allows cells to be recognised as ‘self’ so they will not be attacked by natural killer cells or cytotoxic T cells.
MHC-II is presented on specific WBC, including APC (macrophages and dendritic cells) and helper T cells.

Question 22

Pathogen

Answer 22

A pathogen is a causative biological agent of disease or illness to its host. Can be cellular or non-cellular

Question 23

Allergic response

Answer 23

1. Sensation involves the body’s first encounter with the allergen. The allergen binds with complimentary B cell antibody receptor
2. This initiates a cascade of events that turn B cells into plasma cells that secrete a very high level of IgE antibody, coating the surface of mast cells. No immune response is activated. → sensitisation stage
3. Re-exposure involves the allergen binding with complementarity IgE receptors on the mast cells, triggering degranulation and histamine secretion. This causes heightened inflammation (involve pain, heat, swelling)

Question 24

Cellular pathogen

Answer 24

Classified as living organisms → made up of cells that can reproduce independently without relying on the host machinery.
Bacteria, protozoan, fungi, parasites, arthropods

Question 25

Bacteria

Answer 25

- Prokaryotic cells, no membrane bound nucleus or organelles, contains 1 circular chromosome - Under favourable conditions, enormous numbers can be produced through binary fission (main issue with bacteria- fast rate of multiplying) - Exotoxins - releases defence chemical - Endotoxins- released when cell goes through lysis

Question 26

Protozoan

Answer 26

- Eukaryotes that posses a membrane bound nucleus - Infections caused by protozoa can spread by sexual transmission, or insect vector eg. malaria - Are able to multiply in humans, can survive in human host while causing disease

Question 27

Fungi

Answer 27

- Eukaryotic organisms - Secrete digestive enzymes and other chemicals that can cause disease on host

Question 28

Parasites

Answer 28

- Multicellular eukaryotes - Disease causing organisms

Question 29

Arthropods

Answer 29

Multicellular animals that acts as major vectors of disease in plants / animals

Question 30

Non cellular pathogen

Answer 30

Non- living organisms (no metabolic activity) Not made up of cells and are unable to reproduce without a host (hijack the hosts processes in order to replicate) No membrane or cytosol, just molecular - Virus, viroids, prions

Question 31

Virus

Answer 31

- Non cellular agents consisting of DNA or RNA enclosed within a protein shell (capsid) - Contain enzymes necessary for the reproduction of the virus - reproduce by inserting their nucleic acid into host cell, host cell uses it to make new viruses

Question 32

Viroids

Answer 32

- Piece of RNA/DNA not enclosed by boundary - Usually only infect plants

Question 33

Prions

Answer 33

- Abnormally folded tertiary structure - Fatal degenerative disease of NS / ‘mad cow disease’ - No genetic material

Question 34

Physical barriers animal

Answer 34

Intact skin: The epidermis of the skin is composed of many layers of cells (keratinocytes) with the outermost layer consisting of dead cells. The constant shedding of these dead surface cells is an effective barrier against entry of pathogens. Mucous membranes: line inner spaces of the airways, gut, urogenital tract, consist of epithelial cells. The mucus membranes secrete a thick gelatinous fluid - mucus that can trap particulate matter, including pathogens. Airways include many cells with cilia on outer surfaces, regular beating of cilia moves mucus from deep in airways to back of throat, the mucus that is swallowed will be destroyed by acid in the stomach Ear wax: Reduces the access pathogens have to the eardrum and canal, also protects the ear from dust, foreign particles

Question 35

Physical barriers for plants C TB S CW L T cat to be saw cows walking left today

Answer 35

- Cuticle: Waxy covering on leaves that reduces water accumulation + helps prevent cells becoming infected - Thick bark: external layer that acts similar to intact skin - Stomata: can be closed to prevent pathogens entering; also may sit lower down, to protect the plant. - Cell wall: cellulose wall can protect cells from infection from viruses - Leaf orientation: vertical leaves make it harder for pathogens to attack as water is unable to accumulate on the leaf surface. - Thorns and spikes: modified leaves/ branches which protect the plants from grazing animals.

Question 36

Chemical barriers

Answer 36

Innate barriers that use enzymes to kill pathogens and prevent invasion into a host

Question 37

Chemical barriers for animals

Answer 37

Destroy pathogens on the outer body surface, at body openings, on inner body linings - Lysozyme: (enzyme in body secretions - sweat, mucus, tear, saliva) helps in first line defence that kills pathogens. - Sebum: provides a protective and anti- microbial film on skin. - Stomach acid digestive enzymes: kill pathogens that enter the digestive tract in food and water.

Question 38

Chemical barriers for plants

Answer 38

Produce antimicrobial chemicals, antimicrobial proteins and antimicrobial enzymes that prevent pathogens from entering the plant/ affect pathogen functioning - Tannins: a bitter tasting substance that may deter predators - Saponin: plant proteins that disrupt bacterial and fungal cell membranes

Question 39

Microbiota barriers for animals

Answer 39

'Normal flora’: refers to the non pathogenic bacteria that are the normal residents in particular region of the body (gut, mouth, throat, genital tract) Their presence inhibits the growth of pathogenic microbes Eg. vaginaproduces lactic acid which prevents the establishment of pathogenic microbes.

Question 40

Microbiota barriers for plants

Answer 40

‘Normal flora’: prevents colonisation or growth of pathogen