The Immune System: Vertebrate Immune Systems and Acquired Immunity

Question 1

What is the innate immune system of vertebrates composed of?

Answer 1

• Barrier defenses
• Antimicrobial peptides (AMPs)
• Cellular innate defenses: Specialized WBC, leukocytes, involved in the stages of removal of debris, detecting, consuming foreign bodies, initiating acquired immune response

Question 2

What is the acquired immune system of vertebrates composed of?

Answer 2

• Humoral immune response

- Cell-mediated acquired response

Question 3

What occurs when a splinter, covered by some pathogen, enters the skin?

Answer 3

• Physical damage sets off, disturbs some specialized cells: MAST CELLS, occurring in connective tissue
• When mast cells are ruptured, they release HISTAMINES: Modify surrounding tissues, acting as a signal to other innate defenders
• Histamines causes capillaries nearby to dilate, to become more permeable = VASODILATION

Question 4

What are macrophages?

Answer 4

They are a type of everyday patrollers, that secrete cytokines.

Question 5

What happens when capillaries dilate?

Answer 5

They become more permeable, allowing fluid containing antimicrobial peptides to enter the tissue.
Signals released by the immune cells attract neutrophils.

Question 6

What is the role of neutrophils?

Answer 6

They digest pathogens and cell debris at the site, and the tissue heals.

Question 7

What are cytokines?

Answer 7

Signalling molecules enhance the immune response, which includes increased mucous production.

Question 8

What is one type of inflammatory response?

Answer 8

Allergies: Misguided immune responses

Question 9

What is a systemic inflammatory response?

Answer 9

An exacerbation = Whole-body inflammation (vs local)

It can be triggered by the substances released by macrophages.

Question 10

What is thermogenesis?

Answer 10

An inflammatory response that contributes to the ‘fever’ temperature.

Question 11

How can excessive systemic inflammation (sepsis) be dangerous to the host?

Answer 11

It can be fatal to cells –> Referred to as ‘septic shock’

**Inflammation itself is a normal response

Question 12

What acquired immunity participants do cytokines trigger?

Answer 12

B lymphocytes: Develop in the bone marrow

• Stay in the bone marrow for most of their lives
• Produce pathogen-neutralizing proteins = ANTIBODIES

T lymphocytes: Develop in the thymus

• Cytotoxic T cells: Produce specific biochemicals that target infected host cells
• Helper T cells: Activators for other B and T cells = Signals!

Question 13

What is the important component of acquired immunity?

Answer 13

RECOGNITION! Lymphocytes need to know what they are fighting against (specific pathogens), by relying on chemical recognition of ANTIGENS.

Question 14

What are antigens?

Answer 14

They are substances, segments of organic material, that elicit a response from B or T cells –> Can be recognized

Question 15

How do T or B cells recognize antigens?

Answer 15

Through specific receptors to a pathogen = ANTIGEN RECEPTORS (Lock)

Question 16

What is the epitope?

Answer 16

The small accessible part of an antigen that binds to the antigen receptor (Key).
Sub-portion of the antigen.

Question 17

Antigen receptors belong to the __________, while epitopes belong to the ____________.

Answer 17

Host; Pathogen

Question 18

The antigen receptors of B and T cells have similar __________, but encounter antigens in different ______.

Answer 18

Components; Ways

B cells have two binding sites within their antigen receptors, while T cells have a single one!

**Variability of the variable regions, and the antigen-binding sites.

Question 19

Antigen-specificity is determined by…

Answer 19

Protein sequence in the BINDING REGIONS

This is where the variability in receptors interacts with variability in antigens.

Question 20

What are antibodies (aka immunoglobin)?

Answer 20

Y-shaped proteins produced by B cells.

Start out on the outer surface of mature B cells, but will often be broken off and deployed to circulate in the bloodstream.

It doesn’t NEED to be attached to the B cell to be effective!

Question 21

What do antibodies do?

Answer 21

They bind to the appropriate matching epitope, given its receptor shape.

Note: Antibodies are specific to a particular epitope = PATHOGEN SPECIFICITY

Question 22

What are the three ways in which antibodies act against pathogens?

Answer 22

1. NEUTRALIZATION: Binding of antibodies on the surface of a virus, neutralizing the pathogen –> The pathogen can no longer invade host cells
2. OPSONIZATION: Binding of antibodies on the surface of bacteria, facilitating phagocytosis by macrophages and neutrophils –> Antibodies act like a more favourable site of binding
3. Activation of the COMPLEMENT SYSTEM: When activated by the antibodies, act to destroy/rupture the membranes of foreign cells.
   This crow-bars membrane opens, allowing extracellular fluid to rush in.

Question 23

What are Major Histocompatibility Complex (MHC) molecules?

Answer 23

MHC molecules that already exist in the host cells find ways to bind to already-existing free-floating pieces of the antigens –> Naturally, they rush up to the membrane of the host cell and display an antigen fragment on the surface.

= SELF-FLAGGING!

Question 24

What is the role of cytotoxic T cells in their interaction with MHC molecules?

Answer 24

The antigen-specific cytotoxic T cells recognize/bind to infected cells –> Binds to antigen presented on the surface
Using chemical weapons released, they begin bearing the corresponding antigen and destroying the infected host cell.

INVOLVED IN DESTROYING THE CELLS OF THE HOST = FINDING BAD PARTS OF US, TO SUPPRESS FURTHER SPREAD

Question 25

What is the humoral immune response?

Answer 25

Involves the B cells: Antibodies help neutralize or eliminate toxins and pathogens in the blood and the lymph.

Works through the PRODUCTS of the cell (aka antibodies), not the cell itself.

Question 26

What is the cell-mediated immune response?

Answer 26

In which specialized T cells destroy affected host cells.

Question 27

What do helper T cells do?

Answer 27

They are in the center of the signalling, COORDINATION of the acquired immune response;

They trigger both humoral and cell-mediated immune responses; they signal to B cells to produce antibodies and activate T cells that kill infected cells.

They clone more cytokines that work on both sides of acquired immunity.