MCAT Immune System

Question 1

Innate ( nonspecific) v. Adaptive ( specific) immune systems

Answer 1

• Innate system acts quickly and doesn’t attack specific pathogens.
• Adaptive system attacks specific pathogens and is slower response.

Question 2

Describe the contribution to the immune system that each of these organs have:
- Bone marrow
- Spleen
- Thymus
- Lymph nodes

Answer 2

• Bone marrow - produces leukocytes ( WBCs)
• Spleen - where blood is stored and B-cells are activated.
• Thymus- produces T- cells
• Lymph nodes- where immune cells communicate to mount an attack.
• Other areas include GALT ( gut associated lymphoid tissue), tonsils, adenoids, peyer’s patches, appendix.

Question 3

Process of hematopoiesis

Answer 3

Produces red blood cells, leukocytes, and platelets.

Question 4

What are the divisions of leukocytes?

Answer 4

Granulocytes- contains granules in cytoplasm which contains toxins that are released via exocytosis against foreign invaders. Consists of eosinophils, basophils, neutrophils.

Agranulocytes- doesn’t contain granules in cytoplasm. Contains lymphocytes and monocytes.

Question 5

Humoral immunity v. Cell-mediated immunity

Answer 5

Humoral immunity consist of B-cells and antibodies.

Cell-mediated immunity consists of T-cells.

Question 6

Which organ is the first line of defense of the immune system?

Answer 6

The skin creates a barrier. Sweat has antimicrobial properties.

Skin contains antimicrobial enzymes definsins.

Lysozyme enzyme located in saliva and tears.

Question 7

The role of the gastrointestinal tract in the immune system.

Answer 7

Gut secretes acid which kills them. Our gut flora competes with them for resources making it hard for them to take up residence in the body.

Question 8

Complement

Answer 8

Proteins in the blood that punches holes in pathogens making them osmotically unstable.

• Happens through the classical pathway ( antibody attaches to pathogen) or alternative pathway ( antibody doesn’t attach to pathway).

Question 9

Interferons

Answer 9

Produced by cells of the immune system.

Prevents viral growth and dispersion

Responsible form upregulation of MHC I and II.

Responsible for flu- symptoms.

Question 10

Macrophages

Answer 10

Immune cells that phagocytose the pathogen and present it’s proteins via the MHC ( major histocompatibility complex) for specific immune system learning.

The also release cytokines which recruits other immune cells to the area.

Question 11

What are the two MHC (Major histocompatibility complex)

Answer 11

MHC I -Presented by healthy cells. T-cells uses this to differentiate between healthy and infected cells.

MHC II - Presented by antigen- presenting cells. Antigens presented on surface of cells phagocytosed by macrophages.

Question 12

Macrophages and dendrites has pattern recognition receptors, what are these?

Answer 12

Toll - like- receptor ( TLR) are the most common pattern recognition receptor.

They serve to categorize the invader so a more specific response can be initiated ( ie. fungus, bacteria, virus, etc..)

Question 13

Natural killer cells

Answer 13

Some pathogens and cancer cell can downregulate MHC presentation making it harder to T- cells to detect. NKs are able to detect this downregulated an induce apoptosis.

Question 14

Describe the functions of each of the granulocytes.

• Neutrophils
• Eosinophils
• Basophils

Answer 14

• Neutrophils - most populous and phagocytic. Target bacteria via chemotaxis. Pus is dead neutrophils.
• Eosinophils - Involved in parasitic infections and allergies. Secretes histamines which causes vasodilation and therefore easier travel for immune cells.
• Basophils- secretes histamine in response to allergies.

Question 15

What are the divisions of the adaptive immune system?

Answer 15

• Humoral immunity - Involves B-cells and antibodies.
• Cell- mediated immunity- involves T- cells.

Both B-cells and T-cells are made by bone marrow but T- cells goes to thymus to mature. B-cells remain in bone marrow to mature.

Question 16

B-cells

Answer 16

Creates antibodies ( immunoglobulins, Ig) for specific pathogen recognition.

Activated by spleen and lymph nodes.

Question 17

Difference between free- floating antibodies or B-cell bound antibodies.

Answer 17

Free- antibodies float freely and mark pathogens for phagocytosis ( opsonization) or clump the target pathogens together for being phagocytosed ( aggulutinate).

Free antibodies bind to antigens preventing it from infecting other cells.

Antibodies attached to B- cells- when pathogen attaches to antibody it causes the B- cell to remember it for the adaptive immune system.

Question 18

What happens when B- cells attach to mast cells?

Answer 18

When they bind it causes a release of histamine.

Question 19

What happens to B-cells when they get exposed to a pathogen?

Answer 19

Naive B- cells ( hasn’t been exposed and therefore doesn’t make antibodies) get exposed to a pathogen in the lymph nodes. From here they split into daughter cells with different functions:

• Plasma B- cells - go off to fight infection.
• Memory B-cells - stay in lymph nodes and remember the pathogen to launch an attack ( faster) if pathogen reappear.

Primary response is the initial exposure to B-cells ( 7-10 days). Secondary response is the memory- B cells which will launch a faster response in the future if exposed.

Question 20

Positive and negative selection of T- cells.

Answer 20

Happens in the thymus.
- Positive selection- Choosing T-cells that respond to MHC II class presented while killing the ones that don’t respond.

• Negative selection- choosing against the T-cells that respond to MHC I ( healthy cell presentation).

Question 21

Describe the 3 classes of T-cells.

Answer 21

Helper T- cells ( Th, CD4+ T-cells) - secrete lymphokines which ramps up immune response, these are damaged in HIV/AIDS.

Cytotoxic T- cells ( Tc, CD8+)- responds to MHC II presenting cells so they are best against viral infections. Inject chemicals into the cell.

Supressor T -cells ( regulatory T- cells, Treg)- tone down immune response once it has been dealt with. Works to prevent self- tolerance ( autoimmune)

Memory T- cells- remember the pathogen so it can mount a quicker attack next time.

Question 22

Self- antigens

Answer 22

The proteins and carbohydrate projections on the surface of healthy cells. Allergies and autoimmunity are reactions to these.

Question 23

Active immunity v. Passive immunity

Answer 23

Activity immunity- Protection we get from being exposed to a pathogen to develop memory against it. Happens through vaccines or getting it naturally.

Passive immunity - protection we get from inheriting antibodies. ( ie. babies gaining antibodies from breast milk).

Question 24

Germinal centers

Answer 24

Centers in the lymph nodes where B-cells are exposed to pathogens.