Chapter 15 Innate and Adaptive Immunity

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Innate Immunity Always present Attacks non-self 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)

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Question Tell whether the following statement is 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 T helper cells T suppressor cells Antigen presenting cells Effector cells then carry out the attack on the antigen T cytotoxic (or T killer) 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

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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? T lymphocytes B lymphocytes Antigen presenting cells Leukocytes

Answer T lymphocytes As 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 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 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

T Lymphocytes Differentiate in the Thymus T helper cells (CD4+) CD4 receptors attach to MHC II proteins Start an immune response T cytotoxic cells (CD8+) CD8 receptors attach to MHC I proteins Kill infected cells

Question All but which of the following is true about CD8 receptors? They can be found on cytotoxic T cells. They attach to MHC I proteins. They signal the start of the immune response. 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 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 T helper 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 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? Cytotoxic T lymphocytes Helper T lymphocytes Cytokines B lymphocytes

Answer B Lymphocytes Remember 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: A lack of B cells A lack of Tc cells A lack of TH1 cells 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

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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

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?

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 B memory 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 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 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?

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Question Tell whether the following statement is true or false: Active immunity is achieved much quicker than passive immunity.

Answer False 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.