Chpt 17 Specific Defenses of the Host: Adaptive Immunity

Specific Defenses of the Host: Adaptive Immunity
Chapter 17

Functional divisions of immunity:
Nonspecific immunity
Specific immunity

Specific immunity usually functions when organisms get past nonspecific defenses. Involves recognition and memory. It is slower to respond and uses antibodies and lymphocytes. (Immunity: specific antibody and lymphocyte response to an antigen)

I The adaptive immune system: so called because it adapts to conditions
II Dual nature of the adaptive immune system
A. Humoral immunity: brought about by antibodies (antibody mediated immunity)
1. antibodies (Ab) *antibodies = B cells
a. Proteins made in response to an antigen.
b. involves antibodies made by B cells (made in the bone marrow)
2. Defends primarily against bacteria, bacterial toxins, and freely circulating viruses.
B. Cellular immunity (cell mediated immunity) *Cellular imm = t cells
1. T cells: involves T lymphocytes that act directly against foreign organisms.
a. T cell receptors
2. Activates other immune cells like macrophages
3. Effective against bacteria/viruses within host cells, also against eukaryotic infections.
III Antigens and Antibodies
A. The nature of Antigens (immunogens) Ag: A substance that causes the body to produce specific antibodies or sensitized T cells. (The nature of an antigen is a protein or carbohydrate. A foreign substance to which our bodies produce antibodies.)
1. Antigenic Determinants (epitopes)
a. antibodies recognize and react with specific antigenic determinates.
2. Haptens: low –molecular weight antigens that are not antigenic unless first attached to a carrier molecule.
a. Can bind with a protein or a carb.
b. inflammation starts when phagocytes start to attack it because it sees it as a foreign substance.
c. penicillin





B. The nature of Antibodies (Immunoglobulins Ig): Antibodies are proteins made in response to an antigen.
1. Globulins: proteins of a certain solubility characteristic
2. Antigen bonding sites: each antibody has at least two antigen bonding sites.
a. Binding of antibody to antigen does not destroy the antigen. Instead, the antibody tags foreign cells and molecules for destruction by phagocytes and complement.
b. Valence: the number of antigen bonding sites on the antibody
4. Antibody structure
a. light (L) chains
b. heavy (H) chains
c. variable (V) regions: the end of the Y shaped antibody. V region joins to the epitope.
d. antigen-binding sites
C. Immunogloblulin classes:
1. IgG
a. most abundant
b. crosses placenta to give immunity to the fetus
c. protect against circulating bacteria and viruses
d. neutralize bacterial toxins
e. trigger the complement system
f. bind to antigens to enhance action of phagocytic cells.
g. long lived: its presence may indicate immunity against a past disease.
2. IgM
a. first to appear in response to an antigen, but their concentration declines rapidly.
b. predominant antibody in the ABO blood group antigen reactions.
3. IgA
a. main function is preventing attachment of viruses and certain bacteria to mucosal surfaces.
4. IgD: unknown
5. IgE
a. releases histamine
IV B Cells and Humoral Immunity
A. B cells: A special group of lymphocytes which develop from stem cell precursors. (made and matured in bone marrow)
B. B cells and T cells have specific antigen receptors.
1. A mature B cell recognizes antigen receptors using IgM and IgD antibodies.
2. The intensity of a humoral response is reflected by the antibody titer. (the amount of antibody in the serum)
C. Clonal selection of antibody-producing cells involve T-dependent antigens. (an antigen that requires a Th cell for antibody production)
1. Out of 5 B cells only 1 recognizes the antigen and creates antibodies.
2. It gets divided into:
a. plasma cells: get turned into antibodies
b. memory cells
2. T-independent antigen
D. Diversity of antibodies
V Antigen-antibody binding and its results
A. Antigen-antibody complex
1. affinity
2. specificity
B. Antibody function
1. agglutination
a. hinder pathogenic activity
b. increase chances of phagocytosis
2. neutralization
a. binding and neutralizing toxins
b. block adherence to host cell
3. opsonization
a. stimulate phagocytosis
4. antibody-dependent cell mediated toxicity
5. activation of the complement system
a. non-specific chemical defense against pathogens
b. uses a series of blood serum proteins to destroy invading microbes.
c. Effects of complement activation: See chapter 16 for cascade
i. opsonization or immune adherence: enhanced phagocytosis
ii. membrane attack complex: cytolysis
iii. attract phagocytes.
VI T cells and cellular immunity (Cell mediated Immunity)
A. Intracellular antigens stimulate cell-mediated immunity
B. Specialized lymphocytes, mostly T cells, respond to intracellular antigens
C. T cells differentiate into effector T cells when stimulated by an antigen
D. Some effector T cells become memory cells
E. Classes of T cells
1. Helper T Cells (TH): CD4 adhesion molecule
a. TH1: activate cells related to cell-mediated immunity
b. TH2: activated B cells to produce eosinophils, IgM, and IgE
2. Cytotoxic T cells (TC): CD8 adhesion molecule, attack any cell which is altered
3. Delayed Hypersensitivity T cells (TD)
4. Suppressor T cells
a. turn off immune response when Ag no longer present
VII Antigen-presenting cells (APCs): antigens should be processed to be recognized by T cells.
VIII Extracellular killing by the immune system (did not go over)
IX Antibody-dependent cell mediated cytotoxicity (did not go over)
X Cytokines
A. Chemical messengers
B. Produced mainly by T helper cells
C. Induces the migration of leukocytes on to area of infection: chemotaxis
XI Immunological memory (did not go over)
XII Types of adaptive immunity: Active and Passive Immunity
A. Acquired Immunity
1. Naturally acquired
a. active: antigens enter the body naturally; body produces antibodies and specialized lymphocytes.
b. passive: antibodies pass from mother to fetus via placenta or to infant in the mother’s milk.
2. Artificially acquired
a. active: antigens are introduced in vaccines; body produces antibodies and specialized lymphocytes.
b. passive: preformed antibodies in immune serum introduced in body by injection. (snake venom….when we need it fast)

Various notes:

Sushma likes the term antigenic determinants instead of the term epitopes. Make sure you remember that they mean the same thing.

All enzymes are proteins. If a mo is making an enzyme, we will produce an antibody.

Look at charts in textbook

TC cell = killer cell

Need a lot of T cells to trigger others

I may go blind trying to read the last slide that summarized everything. If I can enlarge it I will.

Study pages: 504-516
Cytokines 518
Immunological memory 519
Types of adaptive immunity 520 – 521

The extra credit III questions are below:

1. Define epitopes and give two characteristics about ideal anitgen. (****she said it should be a protein or a carb with a molecular weight higher than 10, 000)

2. Describe 5 different kinds of immunoglobulins. (so name and characteristics)

3. Name at least three different kinds of anitgen-antibody complexes.

4. What are two major types of T cells and explain the differences among them.

5. List four major differences between Humoral and Cellular immunity. (KNOW THIS QUESTION AS IT ACCOUNTS FOR 15% OF NEXT EXAM QUESTIONS.)