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Page 1: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Antibodies

• Immunoglobulins—gamma globulin portion of blood

• Proteins secreted by plasma cells

• Capable of binding specifically with antigen detected by B cells

Page 2: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 3: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 4: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc. Figure 21.14a

Antigen-bindingsite

Stemregion

Hingeregion

Light chainconstant regionDisulfide bond

Light chainvariable region

Heavy chainconstant region

Heavy chainvariable region

(a)

Page 5: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 6: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc. Table 21.3

Page 7: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 8: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Classes of Antibodies

• IgE

• Monomer active in some allergies and parasitic infections

• Causes mast cells and basophils to release histamine

Page 9: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc. Table 21.3

Page 10: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 11: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 12: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 13: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 14: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Precipitation

• Soluble molecules are cross-linked

• Complexes precipitate and are subject to phagocytosis

Page 15: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 16: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Complement Fixation and Activation

• Activated complement functions

• Amplifies the inflammatory response

• Opsonization

• Enlists more and more defensive elements

Page 17: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc. Figure 21.15

Inactivates by

Antigen Antibody

Fixes and activates

Enhances Enhances Leads to

Phagocytosis

Chemotaxis

Histaminerelease

Inflammation Cell lysis

Agglutination(cell-bound antigens)

Precipitation(soluble antigens)

Neutralization(masks dangerousparts of bacterial

exotoxins; viruses)

Complement

Antigen-antibodycomplex

Adaptive defenses Humoral immunity

Page 18: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Polyclonal antibodies

generally 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).

Page 19: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

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

Page 20: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Anti-antibodies

An immune response can be directedAgainst a part of a particular animalsAntibody common chain.As a consequence, we can detect when such A antibody is present.

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

Page 21: Copyright © 2010 Pearson Education, Inc. Antibodies Immunoglobulins—gamma globulin portion of blood Proteins secreted by plasma cells Capable of binding

Copyright © 2010 Pearson Education, Inc.

Possibilities with conjugates are limitless.