Antigens and Immunogens: Part 2

IgM

• half life 6 days

• 5-10% total serum Ab

• Pentamer

  • highest possible valence of antibodies

IgM

• generally confined to intravascular space

• FIRST Ab PRODUCED

  • primary response

Function of IgM

• excellent agglutinating Ab in diagnostic tests

• activates complements

• binds to FcR on WBC’s

Why is IgM better than IgG at activating compliments?

• because you only need one monomer

what is the secretory component of IgA

• tethers to mucus and protects against proteolytic enzymes

IgA

• 10-15% of total serum Ab

  • monomers and dimers

• most predominant Ab in secretions

• 6 day half life

IgD

• less than 1% of total serum Ab

• found on surface of B lymphocytes

• functions in activation of B cells

• 3 day half life

IgE

• less than 0.001 of total Ab serum

• MAST CELLS, basophils, and activated eosinophils have high affinity receptors for it

• very potent activator of ALLERGIC REACTIONS

• 2 day half life

IgG biological function

• fixes complement, crosses placenta

IgA biological function

• secretory antibody

• alternative pathway

IgM biological function

• fixes complement

IgD biological function

• B lymphocyte surface receptor

IgE biological function

• reaginic antibody

Antigen-Antibody Binding

• takes place with multiple NONCOVALENT interactions between antigen and amino acids

Hydrogen Bonding

• hydrogen atom shared between two electronegative atoms

• H with O,N ect (electronegative atom)

Electrostatic Forces

• oppositely charged groups

• two like electric charges both positive or both negative repel each other along a straight line between their centers

Van der Waals Forces

• positive or negative charged region of a molecule

• caused by correlations in the fluctuating polorizations of nearby particles

Hydrophobic Bonds

• nonpolar molecules clump together in water

Affinity

• strength of a single antigen- antibody interaction

• low (blank) antibodies bind antigen weakly and tend to disassociate more

What determines Affinity

• summation of attractive and repulsive forces

Avidity

• strength with which a multivalent antibody binds to a multivalent antigen

IgM has a greater avidity than IgG Why?

• IgM has more binding sites

Why does IgG have a higher affinity than IgM?

• because IgM is produced first

• IgG undergo affinity maturation

What is the rationale for use in diagnosis and treatment of disease

• they have a very high specificity

• used in a range of clinical and lab tests

Hybridoma Technology Principal

• purification of mAb from heterogeneous mixture not feasible

• preformed by immunizing animals with desired antigen and preparing antisera from their blood

Process of Hybridoma Technology Principal

• normal B cells are exposed to immunogens

• fuse B cells with myeloma cells

Uses of Monoclonal Antibodies

• Immuno-oncology

  • radioactively labeled mAbs can target cancer cells

  • immunotoxins

    • attach toxin to mAb to attack cancer cells

Use of Mice and monoclonal antibodies

• mouse challenged with antigen

• B cells are extracted from spleen o lymph nodes

• B cells are fused with myeloma cells

• fused cells are grown in the presence of drugs that kills myeloma cells and unfused B cells BUT permits the growth of the hybridoma cells

• hybridoma cells are tested for the specific mAb of interest and if produced, the cells are cloned to produce culture of cells making mAb

Use of Mice and monoclonal antibodies

• mouse challenged with antigen

• B cells are extracted from mice

• fused with myeloma cells

• produced hybridomas

• cultured in HAT medium select for positive cells

• monoclonal antibodies are harvested