Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 13 The Immune Response

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Innate Immunity Always present Attacks nonself microbes Does not distinguish between different microbes Mechanisms include: –Epithelial barriers –Phagocytic cells –Plasma proteins –Cell messenger molecules

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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)

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. A vaccination is an example of adaptive immunity.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question AIDS is an example of a disease in which patients are immunocompromised. Which immune cells are affected in AIDS? a.T lymphocytes b.B lymphocytes c.Antigen-presenting cells d.Leukocytes

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer a.T lymphocytes Rationale: 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Two Kinds of Helper T Cells T H 1 cells –Stimulate the cytotoxic T cells and other phagocytic cells to attack the antigen T H 2 cells –Stimulate the B cells to create antibodies against the antigen

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which immune cell creates antibodies in response to antigens? a.Cytotoxic T lymphocytes b.Helper T lymphocytes c.Cytokines d.B lymphocytes

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion Which would cause the most severe immune deficiency? A lack of B cells A lack of Tc cells A lack of T H 1 cells A lack of T H 2 cells A lack of macrophages

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion A 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?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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 area Question: Should she get a booster shot against snakebite before her vacation?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins 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?

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false. Active immunity is achieved much more quickly than passive immunity.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Rationale: 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.