Chapter 17: Adaptive Immunity

Adaptive Immunity

Specific immune defenses that target particular pathogens; acquired through infection or vaccination; develops immunological memory.

Primary Immune Response

First exposure to an antigen; slower response that produces antibodies and memory cells.

Secondary Immune Response

Later exposure to the same antigen; faster and stronger response due to memory cells.

Immunological Memory

Ability of the immune system to recognize a previously encountered antigen and respond more effectively.

Humoral Immunity

Adaptive immunity involving B cells and antibodies that fight extracellular bacteria and toxins and viruses before entering cells.

Cellular Immunity (Cell-Mediated Immunity)

Adaptive immunity involving T cells that target intracellular pathogens and infected body cells.

B Cell vs. T Cell Maturation

B cells mature in red bone marrow; T cells mature in the thymus.

Cytokines

Chemical messengers that allow immune cells to communicate and regulate immune responses.

Major Types of Cytokines

Interleukins regulate immune cells; chemokines attract immune cells; interferons defend against viruses; TNF-alpha promotes inflammation.

Cytokine Storm

Excessive production of cytokines that causes harmful inflammation and tissue damage.

Antigen

Substance usually from a pathogen or foreign material that triggers an immune response.

Epitope (Antigenic Determinant)

Specific region of an antigen that an antibody recognizes and binds.

Antibodies (Immunoglobulins)

Proteins produced by plasma cells that recognize specific antigens and help eliminate foreign substances.

Antibody Structure

Y-shaped molecule consisting of two identical heavy chains and two identical light chains connected by disulfide bonds.

Variable Region (V Region)

Region at the tips of an antibody that binds to specific epitopes.

Constant Region (Fc Region)

Stem of an antibody that interacts with immune cells and complement proteins.

IgG

Most abundant serum antibody at 80%; monomer; crosses placenta; neutralizes toxins and viruses; enhances phagocytosis.

IgM

Approximately 6% of serum antibodies; secreted pentamer; first antibody produced during primary infection; effective in agglutination and complement activation.

IgA

Approximately 13% of serum antibodies; dimer in secretions; found in saliva and tears and mucus and breast milk; protects mucous membranes.

IgD

Approximately 0.02% of serum antibodies; monomer; found on B-cell surfaces and helps initiate immune responses.

IgE

Approximately 0.002% of serum antibodies; monomer; associated with allergic reactions and defense against parasitic worms.

Antibody Structures

IgG and IgD and IgE are monomers; secreted IgM is a pentamer; secretory IgA is a dimer.

MHC Class I

Found on nearly all nucleated body cells; displays intracellular antigens to CD8+ cytotoxic T cells.

MHC Class II

Found on antigen-presenting cells; displays processed antigens to CD4+ helper T cells.

Antigen-Presenting Cells (APCs)

Dendritic cells and macrophages and B cells that process antigens and display fragments to T cells.

T-Cell Receptors (TCRs)

Receptors on T lymphocytes that recognize specific antigen fragments presented by MHC molecules.

B-Cell Activation

Antigen binds B-cell receptor; B cell processes antigen and displays it on MHC II; helper T-cell cytokines activate the B cell.

Clonal Selection

Process in which an immune cell that recognizes a specific antigen becomes activated.

Clonal Expansion

Activated immune cells rapidly multiply to produce many cells with the same antigen specificity.

Plasma Cells

Activated B cells that produce and release antibodies specific to an antigen.

Memory B Cells

Long-lived B cells that respond rapidly to future exposure to the same antigen.

Clonal Deletion

Elimination of potentially harmful immune cells that could attack the body's own tissues.

Affinity

Strength of the bond between an antibody and a specific epitope.

Agglutination

Antibodies cause microorganisms or particles to clump together for easier elimination.

Opsonization

Antibodies coat microorganisms to improve attachment and ingestion by phagocytes.

Neutralization

Antibodies bind viruses or toxins and prevent them from attaching to or affecting host cells.

Complement Activation

Antibody binding can trigger the classical complement pathway; causes cytolysis and opsonization and inflammation.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

Antibodies coat targets such as large parasites; immune cells bind the antibodies and release chemicals that destroy the target.

Helper T Cells (CD4+)

T cells that recognize antigens on MHC II and release cytokines to activate B cells and cytotoxic T cells and macrophages.

Helper T-Cell Activation

APCs present antigen on MHC II; helper T cells recognize it and receive costimulatory signals; activated cells release cytokines.

TH1 Cells

Helper T cells that produce IFN-gamma and IL-2; activate macrophages and cytotoxic cells against intracellular pathogens.

TH2 Cells

Helper T cells associated with IL-4; promote IgE production and eosinophil activity against parasites; involved in allergies.

TH17 Cells

Helper T cells that produce IL-17 and recruit neutrophils against extracellular bacteria and fungi.

Cytotoxic T Lymphocytes (CTLs / CD8+)

T cells that recognize antigens on MHC I and destroy infected or abnormal body cells.

Cytotoxic T-Cell Killing Process

Recognize infected cells displaying antigen on MHC I; release perforin and granzymes to induce apoptosis.

Perforin

Protein released by cytotoxic T cells that helps create pores in target-cell membranes.

Granzymes

Proteins released by cytotoxic T cells that enter target cells and trigger apoptosis.

Apoptosis

Programmed cell death that eliminates infected or abnormal cells and helps prevent viral spread.

Regulatory T Cells (Treg Cells)

T cells that suppress inappropriate immune responses and help prevent attacks against the body's own tissues.

Natural Killer (NK) Cells

Innate immune lymphocytes that destroy virus-infected and tumor cells without requiring specific antigen recognition.

NK Cells and MHC Class I

NK cells can attack abnormal cells that have reduced or missing normal MHC I markers.

Primary vs. Secondary Antibody Production

IgM rises early during the primary response; IgG rises faster and reaches much higher levels during the secondary response.

Class Switching

Process in which antibody production changes from IgM to another class such as IgG or IgA or IgE.

Antibody Titer

Relative amount of a specific antibody present in blood serum.

Active Immunity

Immunity developed when the body's own immune system responds to an antigen and can produce memory cells.

Passive Immunity

Immunity acquired by receiving preformed antibodies from another source; does not create the same immunological memory.

Naturally Acquired Active Immunity

Body develops its own immune response following natural infection.

Naturally Acquired Passive Immunity

Antibodies transferred naturally from mother to baby through the placenta or breast milk.

Artificially Acquired Active Immunity

Vaccination introduces antigens that stimulate the body's own immune response and memory.

Artificially Acquired Passive Immunity

Administration of preformed antibodies that provide protection without requiring the recipient to produce them.

Innate and Adaptive Immunity Connection

Macrophages and dendritic cells engulf pathogens and present antigens to T cells; antibodies can activate complement.