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Antibodies. Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding specifically with antigen detected by B cells. Basic Antibody Structure. T-or Y-shaped monomer of four looping linked polypeptide chains

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antibodies
Antibodies
  • Immunoglobulins—gamma globulin portion of blood
  • Proteins secreted by plasma cells
  • Capable of binding specifically with antigen detected by B cells
basic antibody structure
Basic Antibody Structure
  • T-or Y-shaped monomer of four looping linked polypeptide chains
  • Two identical heavy (H) chains and two identical light (L) chains
  • Variable (V) regions of each arm combine to form two identical antigen-binding sites
basic antibody structure1
Basic Antibody Structure
  • Constant (C) region of stem determines
    • The antibody class (IgM, IgA, IgD, IgG, or IgE)
    • The cells and chemicals that the antibody can bind to
    • How the antibody class functions in antigen elimination
slide4

Antigen-binding

site

Heavy chain

variable region

Hinge

region

Heavy chain

constant region

Stem

region

Light chain

variable region

Light chain

constant region

Disulfide bond

(a)

Figure 21.14a

classes of antibodies
Classes of Antibodies
  • IgM
    • A pentamer; first antibody released
    • Potent agglutinating agent
    • Readily fixes and activates complement
  • IgA (secretory IgA)
    • Monomer or dimer; in mucus and other secretions
    • Helps prevent entry of pathogens
classes of antibodies1
Classes of Antibodies
  • IgD
    • Monomer attached to the surface of B cells
    • Functions as a B cell receptor
  • IgG
    • Monomer; 75–85% of antibodies in plasma
    • From secondary and late primary responses
    • Crosses the placental barrier
classes of antibodies2
Classes of Antibodies
  • IgE
    • Monomer active in some allergies and parasitic infections
    • Causes mast cells and basophils to release histamine
generating antibody diversity
Generating Antibody Diversity
  • Billions of antibodies result from somatic recombination of gene segments
  • Hypervariable regions of some genes increase antibody variation through somatic mutations
  • Each plasma cell can switch the type of H chain produced, making an antibody of a different class
antibody targets
Antibody Targets
  • Antibodies inactivate and tag antigens
    • Form antigen-antibody (immune) complexes
  • Defensive mechanisms used by antibodies
    • Neutralization and agglutination (the two most important)
    • Precipitation and complement fixation
neutralization
Neutralization
  • Simplest mechanism
  • Antibodies block specific sites on viruses or bacterial exotoxins
  • Prevent these antigens from binding to receptors on tissue cells
  • Antigen-antibody complexes undergo phagocytosis
agglutination
Agglutination
  • Antibodies bind the same determinant on more than one cell-bound antigen
  • Cross-linked antigen-antibody complexes agglutinate
    • Example: clumping of mismatched blood cells
precipitation
Precipitation
  • Soluble molecules are cross-linked
  • Complexes precipitate and are subject to phagocytosis
complement fixation and activation
Complement Fixation and Activation
  • Main antibody defense against cellular antigens
  • Several antibodies bind close together on a cellular antigen
  • Their complement-binding sites trigger complement fixation into the cell’s surface
  • Complement triggers cell lysis
complement fixation and activation1
Complement Fixation and Activation
  • Activated complement functions
    • Amplifies the inflammatory response
    • Opsonization
    • Enlists more and more defensive elements
slide17

Adaptive defenses

Humoral immunity

Antigen-antibody

complex

Antigen

Antibody

Inactivates by

Fixes and activates

Neutralization

(masks dangerous

parts of bacterial

exotoxins; viruses)

Agglutination

(cell-bound antigens)

Precipitation

(soluble antigens)

Complement

Enhances

Enhances

Leads to

Inflammation

Phagocytosis

Cell lysis

Chemotaxis

Histamine

release

Figure 21.15

slide18

Polyclonal antibodiesgenerally an immune response activates a number of different plasma cells which can produce only one type of antibody.Each individual antibody will have its own affinity for antigen and specificity for the antigen.The sum of these antibodies that recognize a particular antigen is called Polyclonal antibodies because they arise from many different B cells (plasma cells).

monoclonal antibodies
Monoclonal Antibodies
  • Commercially prepared pure antibody
  • Produced by hybridomas
    • Cell hybrids: fusion of a tumor cell and a B cell
  • Proliferate indefinitely and have the ability to produce a single type of antibody. With a homogenous affinity and specificity.
  • Used in research, clinical testing, and cancer treatment. mAb
anti antibodies
Anti-antibodies

An immune response can be directed

Against a part of a particular animals

Antibody common chain.

As a consequence, we can detect when such

A antibody is present.

Example anti-human IgG antibody (made in rabbits or mice)