6. Immunity with memory Part 1

Question 1

List the cells involved in specific (adaptive) immunity:

Answer 1

• B lymphocytes (B cells)
• Cytotoxic T (Tc or killer T cells) lymphocytes (or cytotoxic T cells)
• Helper T cells and regulatory T cells

Question 2

Where do B cells (lymphocytes) originate and mature, and what is their function?

Answer 2

Develop and mature in the bone marrow, and make antibodies that destroy pathogens by binding to them.

Question 3

Where do T cells (lymphocytes) originate and mature, and what is their function?

Answer 3

First formed in the bone marrow but move to the thymus gland to mature, and kill virus-infected cells.

Question 4

What is the function of helper T cells?

Answer 4

Help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells.

Question 5

What is the function of regulatory T cells?

Answer 5

Are able to inhibit T cell proliferation and cytokine production and play a critical role in preventing autoimmunity.

Question 6

Do all cells contain MHC class I receptors?

Answer 6

Yes, except for red blood cells.

Question 7

What are MHC class I receptors?

Answer 7

Are receptors on the surface of cells that display short polypeptides (antigens), which will identify the cells as ‘self’ if unaffected or ‘foreign’ if infected.
-The polypeptides are presented to lymphocytes which identify them as either ‘self’ or ‘foreign’

Question 8

Describe how antigens are loaded into MHC class I receptors:

Answer 8

As proteins in normal cells are broken down, small antigens (peptides) are loaded into the MHC class I proteins and presented on the surface of the cell

Question 9

How do lymphocytes identify cells as ‘self’ or ‘foreign’?

Answer 9

• If the cell is normal, these antigens tell lymphocytes that the cell is a normal ‘self’ cell
• If the cell mutates (tumor) or is infected by a virus, the antigens presented (and so destroyed) will change and the MCH class I signal will be ‘foreign’

Question 10

Why does every person have a different MHC I signal (unless you have an identical twin)?

Answer 10

Due to genetic differences, every person will have a different MHCI self-signals so everyone’s MHCI signal is unique to that person

Question 11

Which cells have MHC class II receptors?

Answer 11

Only on Antigen Presenting Cells (APC), cells that phagocytose foreign material
-ACPs include: Macrophages, dendritic cells, B cells

Question 12

What is the function of APCs?

Answer 12

Present digested antigens from foreign material to alert other immune cells.

Question 13

Describe the process of the role of an MHC class II cell:

Answer 13

• A macrophage takes up an antigen by phagocytosis
• The macrophage processes the antigen by breaking it into fragments
• A MHC class II protein bind to the processed antigen
• A T cells receptor recognises both the processes antigen and the MHC class II protein

Question 14

What the differences in the type of cells which have MHC class I and MHC class II?

Answer 14

MHC class I receptors are on all nucleated cells (except for red blood cells), whereas, MHC class II proteins are only on APCs (phagocytes, dendritic cells, B cells).

Question 15

What is the difference between MHC class I cells and MHC class II cells in relation to where polypeptides are sourced?

Answer 15

• In MHC class I cells, polypeptides are those that are generated in the cytosol
• In MHC class II cells, polypeptides are those that arise from exogenous antigens (bacteria and viruses that have been phagocytosed)

Question 16

What is the difference between MHC class I cells and MHC class II cells in relation to the type of antigens they display?

Answer 16

• MHC class I cells, display ‘self’ and viral/tumour antigens
• MHC class II cells, display extracellular pathogen antigens

Question 17

How does the body avoid self-recognition and what happens when it doesn’t work?

Answer 17

During maturation, B and T cells are shown different ‘self’ antigens:
-If they don’t react, they continue to mature
-If they do react (bind), the activate apoptosis
When this process does not work correctly, T or B cells will attack self cells (the cause of autoimmune diseases)

Question 18

List and describe the 2 parts of specific immune responses:

Answer 18

• Cell-mediated response: T and cells kill infected cells directly
• Humoral response: B cells produce antibodies that bind to foreign pathogens in the body fluids (Eg. Blood, interstitial fluid)

Question 19

What is humoral immunity?

Answer 19

Where B cells release antibodies that bind to pathogens in body fluids

Question 20

What are antibodies produced by and why? Describe some of their features:

Answer 20

Proteins called immunoglobulins (Ig), which are produced by B lymphocytes.

• Are made in response to an antigen and can recognise and bind to the antigen
• Highly specific (one antigen = one antibody)
• Each antibody has at least two sites that can bind to the antigen
• Antigen binding sites are identical on each antibody (requires a complementary shape)

Question 21

What are macrophages?

Answer 21

Are large phagocytes that become powerful stimulators of an immune response when they engulf a pathogen.

Question 22

What are neutrophils, where are they found, and what is their function?

Answer 22

• Are the most numerous and smallest of the phagocytes
• Found in the blood and tissues
• Rapidly enter sites of inflammation, engulfing the pathogen and then dying in large numbers

Question 23

What are dendritic cells and what is their function?

Answer 23

Phagocytes with membraneous extensions that engulf pathogens, process them and present them to other cells in the immune system.

Question 24

What are plasma cells and what is their function?

Answer 24

B lymphocytes that are differentiated to secrete large amounts of specific antibodies.

Question 25

Describe the humoral response in relation to B cells:

Answer 25

• Need to be activated by an antigen
• Once bound, B cells rapidly divide and the numbers of its clones increase
• B cell clones differentiate into plasma cells or memory cells

Question 26

What is the role of memory cells?

Answer 26

Long-lived cells that rapidly differentiate into antibody-producing plasma cells when the same antigen is encountered.

Question 27

What is the similarities and difference between Dendritic cells and Macrophages?

Answer 27

• They both derived from monocytes
• They both act as antigen-presenting cells and thereby play a crucial role in getting the specific immune response started.
• While Macrophages tend to stay within the fluid compartments of the body, Dendritic cells are more likely to leave the body and moce along the outer surface of the body (Egl. Instines)