Chapter 17–19 Study Guide: Adaptive Immunity, Immune Disorders, and Applications

Specific Immune Response

Properties of Adaptive Immunity

The adaptive (specific) immune response is a highly specialized defense mechanism that targets particular pathogens and retains memory of past exposures.

• Specificity: Adaptive immunity recognizes and responds to specific antigens.

• Memory: After initial exposure, the immune system "remembers" the antigen, resulting in a faster and stronger response upon subsequent exposures.

Types of Specific Immunity

Immunity can be acquired naturally or artificially, and can be either active or passive.

• Naturally Acquired Active Immunity: Occurs when an individual is exposed to a pathogen and mounts an immune response (e.g., recovering from an infection).

• Naturally Acquired Passive Immunity: Transfer of antibodies from mother to child (e.g., via placenta or breast milk).

• Artificially Acquired Active Immunity: Induced by vaccination, where antigens are introduced to stimulate an immune response.

• Artificially Acquired Passive Immunity: Administration of pre-formed antibodies (e.g., antiserum for snake bites).

Humoral Immunity

Antigens, Epitopes, and Haptens

Antigens are molecules recognized by the immune system as foreign. Epitopes are specific regions of an antigen that antibodies or T cell receptors bind to. Haptens are small molecules that are not immunogenic by themselves but can elicit an immune response when attached to a larger carrier.

Antibody Classes and Functions

Antibodies (immunoglobulins) are proteins produced by B cells that bind to antigens. The constant region determines the antibody class and its properties.

• IgD: Functions as a receptor on B cells; involved in initiating immune responses.

• IgM: First antibody produced in response to infection; forms a pentamer; effective at agglutinating antigens.

• IgG: Most abundant in serum; crosses the placenta; activates complement system.

• IgA: Found in secretions (mucus, saliva, milk); forms a dimer; protects mucosal surfaces.

• IgE: Binds to mast cells and basophils; triggers release of histamine upon antigen binding, leading to allergic responses.

Cells Responsible for Humoral and Cellular Immunity

• B cells: Differentiate into plasma cells (which secrete antibodies) or memory B cells.

• Helper T cells (TH cells): Express CD4 receptor (target for HIV); present antigens to B cells and stimulate antibody production.

• Regulatory T cells (TReg): Suppress immune responses to prevent overactivity and autoimmunity.

• Cytotoxic T lymphocytes (CTL): Destroy virally infected cells and cancer cells by releasing cytolytic proteins.

Cellular Immunity

Mechanism of Cellular Immunity

Cellular immunity is mediated by T cells, particularly CTLs, which recognize and destroy infected or abnormal cells.

• CTLs: Survey for cells presenting specific antigens, bind to them, and induce cell death through cytolytic mechanisms similar to complement.

Cytokines

Types and Functions of Cytokines

Cytokines are protein messengers that regulate immune responses by facilitating communication between cells.

• Interleukins: Mediate communication between leukocytes (white blood cells).

• Chemokines: Induce migration of leukocytes to sites of infection or inflammation.

• Interferons: Inhibit viral replication and activate immune cells.

Miscellaneous Applications and Disorders

Monoclonal Antibodies

Monoclonal antibodies are identical antibodies produced by a single clone of B cells. They are generated using hybridoma technology, where a B cell is fused with a myeloma cell to produce a cell line that secretes a specific antibody.

• Applications: Used in diagnostic tests (e.g., ELISA), fluorescent microscopy, and as therapeutic agents.

Systemic Anaphylaxis (Anaphylactic Shock)

Systemic anaphylaxis is a severe, rapid allergic reaction involving widespread release of histamine and other mediators, leading to vasodilation, hypotension, and potentially life-threatening shock.

Erythroblastosis Fetalis (Hemolytic Disease of the Newborn, HDN)

Erythroblastosis fetalis is a condition where maternal antibodies attack fetal red blood cells, often due to Rh incompatibility. This can cause anemia and jaundice in the newborn.

• Prevention: Administration of anti-Rh antibodies (Rho(D) immune globulin) to Rh-negative mothers.

Summary Table: Types of Immunity

Type	How Acquired	Example
Naturally Acquired Active	Exposure to pathogen	Recovery from chickenpox
Naturally Acquired Passive	Maternal antibody transfer	IgG crossing placenta
Artificially Acquired Active	Vaccination	Flu vaccine
Artificially Acquired Passive	Injection of antibodies	Antiserum for rabies

Summary Table: Antibody Classes

Class	Structure	Main Function	Location
IgD	Monomer	B cell receptor	B cell surface
IgM	Pentamer	First response, agglutination	Blood, lymph
IgG	Monomer	Major serum antibody, crosses placenta	Blood, fetus
IgA	Dimer	Mucosal protection	Secretions
IgE	Monomer	Allergic response	Mast cells, basophils

Key Equations and Concepts

• Antibody-Antigen Binding: The specificity of antibody binding is determined by the variable region, which recognizes the epitope of the antigen.

• Complement Activation: IgG and IgM can activate the complement system, leading to pathogen lysis.

Example: IgG crossing the placenta provides passive immunity to the fetus; IgE binding to mast cells triggers allergic reactions.

Additional info: Monoclonal antibodies are widely used in research, diagnostics, and therapy, including cancer treatment and autoimmune disease management. Systemic anaphylaxis requires immediate medical intervention, often with epinephrine.