Antibodies are proteins produced by B cells and plasma cells in response to antigens. They bind specifically to antigens and help destroy or eliminate them. Antibodies form the B cell antigen receptor and are found in highest concentration in blood serum. Immunoglobulins are the proteins that have antibody activity and are classified based on their electrophoretic mobility, molecular weight, and antigenic structure. The major immunoglobulin types are IgG, IgM, IgA, IgD, and IgE, which vary in size and epitope structure.

1. Immunology Lecture Notes: Antibodies Dept. Vet. Microbiology&Parasitology.
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Antibodies
Antibodies are proteins produced by B cells and plasma cells, as a result of the
interaction between B cells and antigen.
1- They bind specifically to antigens and hasten their destruction or
elimination.
2- Antibodies form the B cell antigen receptor (BCR).
3- Soluble antibodies are found in many body fluids but are present in highest
concentration and are most easily obtained from blood stream (serum).
Nature of antibodies:
Antibody molecules are proteins called immunoglobulins (Ig). The term
immunoglobulin is used to designate all proteins with antibody activity as well as
some proteins that have the characteristic molecular structure of antibody
molecules but do not have known antibody activity.
Immunoglobulins may be classified on the basis of:
1- Their electrophoretic mobility.
2- Their molecular weight.
3- Their antigenic structure.
1- Electrophoretic mobility:
The overall charge on any protein depends on its amino acid composition.
Serum electrophoresis: it separates into four major fractions:

2. Immunology Lecture Notes: Antibodies Dept. Vet. Microbiology&Parasitology.
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a- Most negatively charged fraction consists of a single homogenous protein
known as serum albumin.
b- The other three major fractions alfa-globulins, beta-globulins and
gamma-globulins.
2- Molecular weight:
The size of immunoglobulin molecules varies: some are between 150-180
KDa, some are about 200 KDa, some are about 360 KDa and the largest
molecule about 900 K Da.

3. Immunology Lecture Notes: Antibodies Dept. Vet. Microbiology&Parasitology.
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3- Antigenic structure:
a. The major immunoglobulin isotype is called IgG, 160KDa and has
gamma-epitopes.
b. Second major isotype is called IgM, 900 KDa and has meio-epitopes.
c. The third isotype is IgA which is found in body secretions as saliva,
milk and intestinal fluid. It is 360 KDa and has alfa-epitopes.
d. IgD is a B cell antigen receptor found only in very low concentration
in plasma, it is 180 kDa and has delta-epitopes.
e. IgE is a molecule of 200 KDa and has epsilon-epitopes.