> Information Center > Technical FAQs > Antibody Technology Column > How many types of antibodies are there
There are five immunoglobulin classes (isotypes) of antibody molecules found in serum: IgG, IgM, IgA, IgE and IgD. They are distinguished by the type of heavy chain they contain. IgG molecules possess heavy chains known as γ-chains; IgMs have μ-chains; IgAs have α-chains; IgEs have ε-chains; and IgDs have δ-chains.
Antibody classes also differ in their valency, i.e. the number of arms available to bind antigen. This arises from the ability of certain immunoglobulins to form multimers through linkage of their Fc domains via a J chain. For example, IgM is a pentamer of five identical “Y” shaped monomers. Therefore, the complete IgM protein contains 10 heavy chains, 10 light chains and 10 antigen binding arms (giving IgM a valency of 10).
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IgA |
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Heavy chain |
α |
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Light chain |
κ or λ |
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Molecular formula |
(α2κ2)n or (α2λ2)n |
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Valency |
2, 4, 6 or 8 |
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Structure |
Monomers to tetramers (trimers and tetramers are rare, dimers are more common) |
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Abundance in serum (in relation to total immunoglobulins present) |
13% |
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Carbohydrate content |
10% |
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Concentration in serum |
1.0 - 4.0 mg/ml |
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IgA subclasses |
IgA1 |
IgA2 |
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Heavy chain subclasses |
α1 |
α2 |
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Heavy chain MW (kDa) |
55 |
55 |
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Light chain MW (kDa) |
23 |
23 |
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Total MW (kDa) |
160 (serum monomer) |
160 (serum monomer) |
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600 (secretory tetramer) |
600 (secretory tetramer) |
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Distribution |
Intravascular and secretions |
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Function |
Protects mucous membranes |
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IgD |
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Heavy chain |
δ |
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Light chain |
κ or λ |
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Molecular formula |
δ2κ2 or δ2λ2 |
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Valency |
2 |
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Structure |
Monomer |
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Abundance in serum (in relation to total immunoglobulins present) |
0.2% |
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Carbohydrate content |
13% |
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Concentration in serum |
0 - 0.4 mg/ml |
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IgE subclasses |
None |
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Heavy chain MW (kDa) |
62 |
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Light chain MW (kDa) |
23 |
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Total MW (kDa) |
180 |
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Distribution |
Lymphocyte surface |
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Function |
Unclear |
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IgE |
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Heavy chain |
ε |
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Light chain |
κ or λ |
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Molecular formula |
ε2κ2 or ε2λ2 |
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Valency |
2 |
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Structure |
Monomer |
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Abundance in serum (in relation to total immunoglobulins present) |
0.002% |
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Carbohydrate content |
12% |
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Concentration in serum |
10 - 400 ng/ml |
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IgE subclasses |
None |
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Heavy chain MW (kDa) |
70 |
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Light chain MW (kDa) |
23 |
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Total MW (kDa) |
190 |
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Distribution |
Basophils and mast cells (in saliva and nasal secretions) |
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Function |
Protects against parasites |
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IgG |
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Heavy chain |
γ |
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Light chain |
κ or λ |
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Molecular formula |
γ2κ2 or γ2λ2 |
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Valency |
2 |
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Structure |
Monomer |
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Abundance in serum (in relation to total immunoglobulins present) |
80% |
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Carbohydrate content |
3% |
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Concentration in serum |
10 - 16 mg/ml |
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IgG subclasses |
IgG1 |
IgG2 |
IgG3 |
IgG4 |
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Heavy chain subclasses |
γ1 |
γ2 |
γ3 |
γ4 |
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Heavy chain MW (kDa) |
50 |
50 |
60 |
50 |
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Light chain MW (kDa) |
23 |
23 |
23 |
23 |
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Total MW (kDa) |
150 |
150 |
170 |
150 |
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Distribution |
Intravascular and extravascular |
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Function |
Secondary response antibody |
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IgM |
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Heavy chain |
μ |
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Light chain |
κ or λ |
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Molecular formula |
(μ2κ2)5 or (μ2λ2)5 |
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Valency |
10 |
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Structure |
Pentamer |
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Abundance in serum (in relation to total immunoglobulins present) |
6% |
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Carbohydrate content |
12% |
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Concentration in serum |
0.5 - 2.0 mg/ml |
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IgM subclasses |
None |
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Heavy chain MW (kDa) |
70 |
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Light chain MW (kDa) |
23 |
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Total MW (kDa) |
970 |
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Distribution |
Mainly intravascular |
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Function |
Primary response antibody |
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