Chapter 7 - Immune Defences Against Pathogens

Question 1

WBC derive from?

Answer 1

Multipotent stem cells in the bone marrow.

Question 2

First line of defence

1. Specific or non-specific?
2. Innate or adaptive immunity?
3. Plant defences?
4. Examples first line defences in humans

Answer 2

1. Non-specific
2. Innate - always present regardless if a pathogen is present or not.
3. Plants - cell wall provides physical barrier. Chemical defences such as ability to produce antibiotics, enzymes and other chemicals. Cells can self-destruct.
4. Examples:
   • intact skin - anatomical barrier - sweat, sebum
   • eyes - washing by tears, lysozyme
   • digestive tract - stomach acidity

Question 3

Purpose of a fever

Answer 3

Above 37.8°C, bacterial toxins reduce the rate of most bacteria, allows more time for other defences.

Question 4

Lymphatic system

1. Role/function?
2. Lymph: What? Does?
3. Lymph node: what? Does?

Answer 4

1. Open system that collects interstitial fluid; returns fluid to the blood and aids in body defence.
2. Lymph = fluid that remains in the closed circulatory loop; too large to pass through capillary membranes.
3. Lymph node = ‘checkpoints’ that monitor and cleanse lymph as it filters through.

Question 5

Mammalian immune system is made up of?

Answer 5

• Primary lymphoid organs = thymus and bone marrow.

* Secondary lymphoid organs = lymph nodes, spleen, appendix, tonsils, adenoids.

Question 6

Lymphatic system
1. What at occurs at the thymus and bone marrow?

2. What happens at secondary organs?

Answer 6

1. Where new lymphocytes are made and educated.

2. Where adaptive immune response occurs.

Question 7

What occurs in the lymphatic system (process)?

Answer 7

1. The heart pumps blood at high pressure. As a result, fluid leaks out of the blood capillaries.
2. When the pressure in the interstitial space becomes greater than the pressure inside the lymphatic capillary, flaps of the lymphatic capillary push open and take in the fluid. The fluid is now called lymph.
3. Lymph flows through the lymphatic vessels. Along these vessels are lymph nodes, which house lymphocytes - T cells and B cells.
4. The lymph continues through the lymphatic vessel and more lymph nodes, and returns back into the circulatory system just before it enters into the heart.

• The lymph moves into the vena system where pressure is very low

Question 8

Purpose of valves?

Answer 8

Ensures that lymph fluid will not leak back into the interstitial space

And prevents lymph from flowing backwards.

Question 9

How does the lymphatic system help fight infection?

Answer 9

1. The lymphatic system produces white blood cells, known as lymphocytes. There are 2 types - T cells and B cells.
2. As they reach the lymph nodes, they are filters and become activated by contact with foreign substances in the lymph fluid.
3. As they become activated, they form antibodies (or produce from memory is encountered in the past) and start to defend the body.
4. Activated lymphocytes pass further through the lymphatic system to reach the blood stream so they can spread the immune response throughout the body, through the blood circulation.

Question 10

Define lymphocyte

Answer 10

A type of white blood cell that is made in the bone marrow and found in the blood and in lymph tissue, responsible for immune responses.

Question 11

Second line of defence

1. Specific or non-specific?
2. Innate or adaptive immunity?
3. Defensive cells involved?

• fever, chemical signals, inflammation

Answer 11

1. Non-specific.
2. Innate
3. Phagocytes (Types: neutrophils & macrophages) and natural killer cells (NK cells)

Question 12

Process of phagocytosis

Answer 12

1. Detection and interaction - microbe coated in opsonins is detected by the phagocyte and attaches to it.
2. Engulfment - opsonin markers trigger engulfment of the microbe, which is taken in by endocytosis.
3. Phagosome forms - enclosing the microbe in a membrane.
4. Fusion with lysosome - fusions forms a phagolysosome, containing powerful antimicrobial proteins.
5. Digestion - microbe is broken down into its chemical constituents.
6. Discharge - indigestible material is discharged from the phagocyte via exocytosis.

Question 13

Antimicrobial proteins in the second line of defence:

1. Compliment
2. Cytokines

Answer 13

1. Compliment
   • in blood plasma and tissue fluid
   • proteins that tag pathogens
   • can cause pore formation
2. Cytokines
   • proteins that affect cell behaviour and signalling molecules.
   • can induce growth, movement, differentiation or death of a cell

Question 14

Second line of defence: process of inflammation

• symptoms = swelling, redness, heat, pain

Answer 14

1. When mast cells are damaged, they release histamine and prostaglandins. Pathogen binds to receptors that induces the cell to release cytokines, calling more immune cells to the infection site.
2. Prostaglandins cause increased blood flow and chemical signals that brings white blood cells to the infection site.
3. Histamine cause capillaries to widen and increase permeability, releasing leucocytes and clotting factors into damaged tissue.
4. Phagocytes squeeze between cells of blood vessel walls where they engulf bacteria, dead cells and cellular debris.
5. Platelets move out of the capillary to seal the wounded area. Functioning cells or supporting connective cells create new tissue to replace dead or damaged cells.
6. An abscess (puss) forms due to the collection of dead phagocytes, damaged tissue and various body fluids.

Question 15

Cell types involved in innate immune response

Answer 15

• monocytes - in blood, differentiate into macrophages.
• neutrophils - in the blood, most abundant WBC, phagocytosis of foreign objects, first cells to arrive, short lived, die by apoptosis.
• natural killer cells (NK cells) - in the blood, elimination of virus-infect cells and cancer cells, insert holes in plasma membrane of foreign cells (induce apoptosis) and produce cytokines.
• macrophages - in tissues, patrol tissues for infection/injury, identify and eliminate foreign objects by phagocytosis, initiate acute inflammatory response by secretion of cytokines.
• dendritic cells - in tissues, identify pathogens and secrete antiviral cytokines, phagocytosis of foreign objects, survey cells and tissues.
• mast cells - release chemical signals that attract other immune cells to infection site.

Question 16

Third line of defence

1. Specific or non-specific?
2. Innate or adaptive?
3. Immune cells involved and their functions?

Answer 16

1. Specific
2. Adaptive
3. • Cytotoxic T cells (Tc cells) = secrete cytokines, kill target cells by creating pores in membranes.
   • Helper T cells (Th cells) = activates cytotoxic T cells and B cells.
   • B cells = produce memory B cells and plasma cells (make antibodies).

Question 17

Lymphocytes

1. Start where?
2. Stay and mature into?
3. Leave to? And mature into?

Answer 17

1. Bone marrow
2. B cells
3. Thymus gland —> T cells

Question 18

Third line of defence: process

Answer 18

1. A dendritic cell or a macrophage engulfs the antigen by phagocytosis and uses fragments of the antigen to display on their class II MHC molecules.
2. A receptor on a Th cell recognises the antigen on the dendritic cell or macrophage and binds with it, which then activates Tc cells and B cells.
3. Tc cells will secrete cytokines and directly kill target cells by creating pores in membranes of foreign objects, while B cells will undergo repeated division to form a clone of cells, either plasma or memory B cells.
4. Plasma cells will secrete antibodies into the bloodstream to neutralise infectious agents, while memory B cells will remember infectious agents, circulate through circulatory and lymphatic system and rapidly produce antibodies if they re-encounter the same antigen.

Question 19

Antibodies (immunoglobulin)

• 3 functions of antibodies

Answer 19

1. Neutralisation - surround, bind to and inactivate an infectious agent (clump).
2. Opsonisation - pathogen is marked for ingestion and eliminated by phagocytes.
3. Degranulation - killing of a marked target cell through lysis (holes in membrane)

Question 20

Difference between humoral immunity and cell-mediated immunity.

Answer 20

Cell-mediated immunity involves the role and action of T cells, whereas humoral immunity involves the role and action of B cells and their antibodies.

Question 21

Clonal selection

1. Basic purpose
2. Process

Answer 21

1. Provides the basis for immunological memory.
2. An antigen binds to its ‘selected’ B cell (has complimentary shape to B cell receptor), which then activates that B cell, causing it to instigate cycles of cell division. This produces many identical B cells which produce the same kind of antibody.