Biology SAC 3

Immunity

What is an antigen?

A molecule or part of a molecule that can elicit an immune response. They are usually found expressed on the surface of the plasma membrane of cells, or floating freely in body fluids.

How does the body distinguish self from non-self?

By using protein markers on the surface of their cells called MHC’s that differ in each individual.

Theres MHC-1, and MHC-2

What is MHC-1?

Found on all nucleated body cells, MHC-1 allows natural killer cells or cytotoxic T-cells to attach and identify as self. They do this by presenting proteins that are being made inside the cell.

How can MHC-1 help identify virus infected cells?

Host cells' MHC-1 will present viral proteins on the outside of the cell membrane, and will signal abnormality to body as non-self.

What is MHC-2?

Found only in antigen presenting cells, MHC-2 help activate the adaptive immune response.

What are antibodies?

Proteins produced by B lymphocytes in response to an antigen, which can be found bound to the surface of B lymphocytes or secreted by them.

What is a B Lymphocyte?

B Lymphocytes are receptors that are membrane bound antibodies that bind to free antigens or antigens on the surface of pathogens.

What is a T Lymphocyte?

Receptors that recognise antigens presented by their own immune cells.

What is the difference between infectious and non-infectious diseases?

Infectious diseases are ones caused by pathogens, whilst non-infectious diseases are caused by genetic variables or lack of nutrients.

What are the 2 types of pathogens?

Primary pathogens - cause disease any time they are present.

Opportunistic pathogens - only cause disease whne the hosts defences have been weakened

How do bacterial disease symptoms arise?

Result from the destruction of cells and tissues by bacterial enzymes, irritation from bacterial waste products or reactions to bacterial toxins that impact normal cellular functions.

How does a virus replicate?

1. the virus binds to the host cells plasma membrane

2. the virus is engulfed into the cell via endocytosis

3. The viral contents are released into the cell, and enters the nucleus, where it is replicated by viral RNA polymerase.

4. Viral mRNA is used to make viral proteins

5. New viral particles are made and released into the extracellular fluid, as the host cell continues to produce new virus.

What are the 6 cellular pathogens and then 3 non-cellular pathogens?

1. Bacteria

2. Protozoans

3. Fungus

4. Oomycetes

5. worms

6. Arthropods

BPFOWA

1. viruses

2. viroids

3. prions

What are the 2 most important white blood cells?

• Phagocytes

• Lymphocytes

First line of defence

Stops pathogens from entering the body

e.g: INTACT skin, mucous membranes

Second line of defence

The innate immune response, which activates immediately when pathogens breach your external barriers.

e.g: blood clotting, or a fever

Third line of defence

The adaptive immune response, which uses specialized lymphocytes (B-cells and T-cells) to target specific pathogens, neutralize them, and create long-lasting immunological memory.

e.g: Lymphocytes, Antibodies.

What are 2 physical barriers in animals?

• Intact skin (effective barrier to most microorganisms)

• Mucous membrane (foreign particles get caught in mucus, and are carried by the beating cilia, where they are swallowed, and destroyed)

What are 2 chemical barriers in animals?

• Acid in the stomach (destroys microbes that are swallowed)

• Lysozyme (found in tears, and other bodily fluids that split bacterial walls and cause them to burst.)

What are 2 microbiological barriers in animals?

• Non-pathogenic microbes that live on the surface of the body

• Presense of normal flora that prevents growth and colonization of other bacteria.

What are 2 mechanical barriers in plants?

• Waxy cuticle and bark - provides a physical barrier in the same way skin does

What are 2 chemical barriers in plants?

• Saponins - inactive compounds stored in vacuoles that may cause damage to teh cell membrane of pathogens.

• Defensins - Proteins that block the growth of pathogens (usually released by germinating seeds)

Phagocytosis?

• The phagocyte recognises specific non-self antigens on the pathogens surface and extends and engulfs it.

• The membrane pinches inward to form a vesicle known as a phagosome inside the cell, enclosing it

• The phagosome fuses with a lysosome and hydrolytic enzymes break down the pathogen, and waste products are expelled.

What does a neutrophil do? (main type of white blood cell)

• Manufactured in the bone marrow, they travel around and engulf and digest bacteria.

• They release antimicrobial compounds that disrupt bacteria and fungal membranes.

• They release cytokines that attract other immune cells and cause inflammation.

What do macrophages do? (main type of white blood cell)

• Engulf foreign bodies in tissues

• They present antigens to activate adaptive immunity and release cytokines to regulate inflammation and tissue repair.

• (horseshoe shaped nuclei)

What do monocytes do? (main type of white blood cell)

• They circulate in the bloodstream to engulf pathogens and debris before migrating into tissues to differentiate into macrophages

What do dendritic cells do? (main type of white blood cell)

• Dendritic cells are specialized antigen-presenting cells that phagocytose pathogens in tissues exposed to the environment, then migrate to lymph nodes to activate naive T cells.

What do natural killer cells do?

• They recognize specific antigens on infected or abnormal host cells and destroy them by releasing perforin and other chemicals to trigger apoptosis.

What do mast cells do?

• Cells found in tissues that release histamine, heparin, and cytokines when activated by pathogens or allergens, driving inflammation and allergic responses

What is the role of complement proteins?

• Contributes to inflammation by increasing the local permeability of capillaries and attracting phagocytes

• Destroying bacterial membranes by sticking and punching holes in them.

• Attract phagocytes and stimulate them to become more active.

• Op-SON-ising pathogens - Binding to pathogens singnalling for phagocytosis.

What are cytokines?

• Signalling molecules for the immune system,

• indicate the presence of damage or foreign body.

• Promote growth and poliferation of lymphocytes, induce fever, and promote antibody responses.

What is an interferon?

• They are signalling proteins (cytokines) released by virus-infected host cells to warn neighbouring uninfected cells, stimulating them to produce antiviral proteins that block viral replication

what are chemokines?

• Chemical attractants to guide migrating immune cells to the site of an infection or tissue damage

What are the steps of the inflammatory response? (important and long process)

1. The pathogen enters the first line of defence (e.g: thru a cut)

2. Injured cells release cytokines

3. Platelets release clotting factors at the site of the cut

4. Cytokines attract neutrophils, macrophages and mast cells to the area

5. The mast cells release histamines which increase blood dilation and permeability, thus allowing blood containing complement proteins and leukocytes to come to the area

6. Neutrophils are activated and secrete factors as defensins and H2O2 that kill pathogens

7. Macrophages are activated and secrete cytokines and other debris.

8. The inflammatory response continues until the pathogen is eliminated and the wound is healed.

What is a fever?

• A defence mechanism against a bacterial infection.

• Caused by an increase in body temp due to resetting of the body temperature set point in the hypothalamus of the brain to a higher temp

• Triggered by bacterial toxins

• Reduces the growth rate of bacteria and allows time for other defence responses to deal with the bacteria.

What does the higher temperature induced from a fever do?

• Inhibits the growth of bacteria and viruses

• Speeds up metabolic processes, helping the body tissue repair faster.

What are the general functions of the lymphatic system?

1. Returns fluid from tissues to blood

2. Returns large molecules to blood

3. Absorb and transport fats

4. Hemopoiesis

What is lymph?

• The clear fluid that enters the lymphatic system after being collected from the spaces between cells, carrying white blood cells, fats, proteins, and any trapped pathogens.