chapter 13 the immune response

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Chapter 13The Immune Response


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 cells that attack the specific antigen)


Question

Tell whether the following statement is true or false.A vaccination is an example of adaptive immunity.


Answer

True Rationale: 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


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 being displayed will respond to it


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 lymphocytesRationale: As you can see in slide 8, 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 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 tell

helper T cells to start an immune response against the antigen

• MHC I proteins tell cytotoxic T 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


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 are 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.Rationale: CD8 receptors do all of those things but 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 Helper T Cells

• TH1 cells – Stimulate the cytotoxic T 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– Inflammatory mediators: cause fever; attract

WBCs to the infection– Growth factors: cause WBCs to divide and mature– Cell communication molecules: used to control

activity of other WBCs


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 lymphocytesRationale: 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.


DiscussionWhich 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 mucous 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


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 antibodies against 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 Immunity

Scenario• 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 areaQuestion:• 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.)

Discussion• The woman says that since her immunity went to

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


Question

Tell whether the following statement is true or false.Active immunity is achieved much more quickly than

passive immunity.


Answer

FalseRationale: In 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.

chapter 13 the immune response

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