Antibodies are the made up of immunoglobulin.
There are 5 different isotypes of immunoglobulins based upon the differences of heavy chain constant region. this 5 isotypes are
1) Immunoglobulin G (IgG)
2) Immunoglobulin M (IgM)
3) Immunoglobulin A (IgA)
4) Immunoglobulin E (IgE)
5) Immunoglobulin D (IgD)
Each of this 5 isotypes contain different heavy chains
IgG contain gamma( γ), IgM contain Mu(μ), IgA contain alpha( α), IgE(ε) contain epsilon and IgD(δ) contain delta type of heavy chains.
The length of the constant region of the heavy chains is either 330 amino acid
residues (for alpha,gamma and delta chains) or 440 amino acids (for Mu and epsilon chains).
1) IgG
- M.wt. - 150 KiloDalton
- IgG, the most abundant class in serum, constitutes about 80% of the total serum immunoglobulin.
- It consists of 2 heavy chains and 2 kappa or 2 lamda light chains.
- Four types of IgG found in human. It is contain subisotype of heavy chains like
- Gamma1 for IgG1
- Gamma2 for IgG2
- Gamma3 for IgG3
- Gamma4 for IgG4
The structural characteristics that distinguish these subclasses from one another are the size of the hinge region and the number and position of the interchain disulfide bonds between the heavy chains.
IgG1,IgG2a,IgG2b,IgG3 found in mice. It is contain gamma1, gamma2alpha, gamma2beta, and gamma3 heavy chains respectively.
- IgG1, IgG3, and IgG4 readily cross the placenta and play an important role in protecting the developing fetus.
- IgG3 is the most effective complement activator,followed by IgG1; IgG2 is less efficient, and IgG4 is notable to activate complement at all.
- IgG1 and IgG3 bind with high affinity to Fc receptors on phagocytic cells and thus mediate opsonization. IgG4 has an intermediate affinity for Fc receptors, and IgG2 has an extremely low affinity.
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