CHAPTER 15

INNATE AND ADAPTIVE IMMUNITY

CHAPTER 15

INNATE AND ADAPTIVE IMMUNITY

Essentials of Pathophysiology

PRE LECTURE QUIZ (TRUE/FALSE)

Active immunity is acquired through immunization or actually having the disease.

T lymphocytes are responsible for humoral immunity.

Adaptive immunity (also called acquired immunity) refers to immunity that is acquired through previous exposure to infectious and other foreign agents.

The thymus does not play a role in the immune response.

Passive immunity represents a temporary type of immunity that is transferred from another source, such as in utero transfer of antibodies from mother to infant.

T

F

T

F

T

PRE LECTURE QUIZ ________________ immunity (also called natural

or native immunity) consists of cellular and biochemical defenses that are in place before infection and respond rapidly to it.

There are five classes of __________________: IgG, IgA, IgM, IgD, and IgE, each with a different role in the immune defense strategy.

The __________________, a large secondary lymphoid organ located high in the left abdominal cavity, functions to filter antigens from the blood and is important in the response to systemic infections.

Substances that are foreign to the host and can stimulate an immune response are known as __________________.

____________________ is the class of immunoglobulin that is involved in allergic and hypersensitivity reactions.

Antigens

IgE

Immunoglobulin

Innate

spleen

 

IMMUNE MECHANISMS

IMMUNE SYSTEM

INNATE IMMUNITY Always present Attacks nonself microbes Does not distinguish between different

microbes Mechanisms include:

Epithelial barriers Phagocytic cells Plasma proteins Cell messenger molecules

ADAPTIVE IMMUNITY

Attacks specific microbes (antigens)

Develops after exposure to the specific antigen

Mechanisms include:

Humoral immunity (antibody proteins in the blood that attack the specific antigen)

Cell-mediated immunity (phagocytic & TC cells that attack the specific antigen)

Proteins we make that attack specific invaders

Foreign substance that causes us to Generate Antibodies

AntiGen

QUESTION

True or False:A vaccination is an example of adaptive

immunity.

ANSWER

True

In adaptive/acquired immunity, specific antigens are attacked, and immunity develops after exposure to the specific antigen. When you get a vaccine, you are getting a live, weakened, or dead microbe (a specific antigen). Your body develops antibodies to attack that antigen after you are exposed.

IMMUNE CELLS Regulatory cells control the immune

response Helper T cells Suppressor T cells Antigen-presenting cells

Effector cells then carry out the attack on the antigen Cytotoxic T (or killer T) cells B cells (produce antibodies) Leukocytes

ANTIGEN-PRESENTING CELLS TELL THE IMMUNE SYSTEM WHAT TO ATTACK

• Eat the invading antigen

• Break it down into pieces called epitopes

• Put epitopes on the cell surface, attached to MHC II proteins

APC

NATURAL KILLER CELL (NK)

ANTIGENS ATTACHED TO MHC PROTEINS

CAN BE “SEEN” BY IMMUNE CELLS The immune cells

have receptors that attach to MHC proteins and “see” the antigen

They also have antigen receptors

Only those T cells whose antigen receptors “fit” the antigen displayed will respond to it

APC

MHC I AND MHC II PROTEINS BOTH DISPLAY ANTIGENS

MHC II proteins display antigens eaten by a phagocytic cell

MHC I proteins display antigens made inside an infected cell

MHC I AND MHC II PROTEINS BOTH DISPLAY ANTIGENS (CONT.)

MHC II proteins on APC cells tell helper T cells to start an immune response against the antigen

MHC I proteins on any body cell tell cytotoxic T cells to kill the infected cell before it can infect other cells

On All cells

Only On APC cells

CD 4 is required for docking with

MHC II

CD 8 is required for docking with

MHC I

Stimulate B and TC cells

QUESTION

AIDS is an example of a disease in which patients are immunocompromised. Which immune cells are affected in AIDS?

a. T lymphocytesb. B lymphocytesc. Antigen presenting cellsd. Leukocytes

ANSWER

a. T lymphocytesAs you can see in slide 08, the virus is

attaching itself to CD4 receptor sites, located on T cells (T lymphocytes). Only helper T cells have this receptor.

MHC I AND MHC II PROTEINS

MHC II proteins display antigens eaten by a phagocytic cell

MHC I proteins display antigens made inside an infected cell

MHC I AND MHC II PROTEINS

MHC II proteins tell T helper cells to start an immune response against the antigen

MHC I proteins tell T cytotoxic cells to kill the infected cell before it can infect other cells

WHERE DO LYMPHOCYTES COME FROM?

Stem cells in the bone marrow or fetal liver

B cells mature in the bone marrow

T cells mature in the thymus

Then they move to the lymph nodes to wait for an antigen-presenting cell to activate them

Bone Marrow

T LYMPHOCYTES DIFFERENTIATE IN THE THYMUS

Helper T cells (CD4+) CD4 receptors

attach to MHC II proteins

Start an immune response

• Cytotoxic T cells (CD8+)

– CD8 receptors attach to MHC I proteins

– Kill infected cells

QUESTION

All but which of the following is true about CD8 receptors?

a. They can be found on cytotoxic T cells.b. They attach to MHC I proteins.c. They signal the start of the immune

response.d. They differentiate in the thymus.

ANSWER

c. They signal the start of the immune response.

CD8 receptors do all of those things, but they don’t kick off the immune response (the helper T cell does that). CD8 receptors are found on cytotoxic T cells; as the name implies, they kill the infected cell.

TWO KINDS OF T HELPER CELLS

TH1 cells

Stimulate the T cytotoxic cells and other phagocytic cells to attack the antigen

TH2 cells

Stimulate the B cells to create antibodies against the antigen

TH CELLS RELEASE CYTOKINES

Cytokines are chemicals that control the immune response of the cells with receptors (“ears”) Inflammatory mediators: cause fever; Chemotaxic cytokines attract WBCs to the

infection Growth factors: cause WBCs to divide and

mature Cytokines are cell communication

molecules: used to control activity of other WBCs

Cytokines are the “Voice” of the TH cells HELLO

B LYMPHOCYTES

Like T cells, B cells have antigen receptors

They can only be activated to attack the antigen if a helper T cell shows it to them

ACTIVATED B CELLS DIVIDE INTO TWO KINDS OF CELLS:

Memory B cells remain in the body In the future, they will

fight off the antigen without a helper T cell telling them to do so

Plasma cells create antibodies, - special proteins designed to attach to that antigen and destroy it

QUESTION

Which immune cell creates antibodies in response to antigens?

a. Cytotoxic T lymphocytesb. Helper T lymphocytesc. Cytokinesd. B lymphocytes

ANSWER

d. B lymphocytes

Rationale: Remember that antibodies are created in response to antigens. B lymphocytes have antigen receptors and are activated to attack a specific antigen if a helper T cell directs them to do so.

ACTIVATED B CELLS DIVIDE INTO TWO KINDS OF CELLS: Memory B cells remain in the body

In the future, they will fight off the antigen without a T helper cell telling them to do so

Plasma cells create antibodies, special proteins designed to attach to that antigen and destroy it

QUESTION

Which immune cell creates antibodies in response to antigens?

a. Cytotoxic T lymphocytesb. Helper T lymphocytesc. Cytokinesd. B lymphocytes

ANSWER

d. B LymphocytesRemember that antibodies are created in

response to antigens. B lymphocytes have antigen receptors and are activated to attack a specific antigen if a T helper cell directs them to do so.

DISCUSSION:

Which would cause the most severe immune deficiency?

A lack of B cells

A lack of Tc cells

A lack of TH1 cells

A lack of TH2 cells

A lack of macrophages

ANTIBODIES OR IMMUNOGLOBULINS

IgG: circulates in body fluids, attacking antigens

IgM: circulates in body fluids; has five units to pull antigens together into clumps

IgA: found in secretions on mucus membranes; prevents antigens from entering the body

IgD: found on the surface of B cells; acts as an antigen receptor

IgE: found on mast cells in tissues; starts an inflammation

ANTIBODY/IMMUNOGLOBIN STRUCTURE

COMPLEMENT PROTEINS Highly toxic proteins Circulate in the

blood in an inactive form

When an antibody attaches to an antigen, the resulting immune complex can activate complement

Complement then destroys the antigen

DISCUSSIONA woman has type A blood. What antigens does she have on the

surface of her red blood cells? What RBC antibodies against other RBC

antigens has her body produced? What will happen if she is given type B

blood? What will happen if her blood is given to a

person with type B blood? What will happen if she is given type O

blood?

PRIMARY IMMUNE RESPONSE The macrophage

must eat the antigen, then present it to TH cells

TH cells must activate B cells

B cells produce antibodies

Then plasma antibody levels rise

This can take 2–3 weeks

Vaccination produces a primary immune response

SECONDARY IMMUNE RESPONSE Memory B cells

respond to the antigen immediately

Plasma antibody levels rise within days

Booster shots cause a secondary immune response so antibody levels will be high before the disease is encountered

ACTIVE IMMUNITY VS. PASSIVE IMMUNITYScenario

A woman was bitten by a rattlesnake last summer; she received antiserum against the snake venom, and she survived

This summer she will be vacationing in the same area

Question:

Should she get a booster shot against snakebite before her vacation?

ACTIVE IMMUNITY VS. PASSIVE IMMUNITY (CONT.)

Scenario

A woman’s baby is HIV-positive

Questions:

Does this mean the baby has HIV?

Does it mean the father has HIV?

Does it mean the mother has HIV?

ACTIVE IMMUNITY VS. PASSIVE IMMUNITY(CONT.)Scenario:

A woman's baby is HIV-positive

Question:

Does this mean the baby has HIV?

Does it mean the father has HIV?

Does it mean the mother has HIV?

ACTIVE IMMUNITY VS. PASSIVE IMMUNITY(CONT.)Discussion: The woman says that since her

immunity went to her baby, the baby will not need any vaccinations. Is this correct?

QUESTION

True or False:Active immunity is achieved much

quicker than passive immunity.

ANSWER

FalseIn active immunity, an individual is

exposed to an antigen, the immune response begins, and antibodies are formed in 7–10 days. In passive immunity, antibodies are created outside the host and injected, giving the individual immunity immediately.