3. IgA:
It constitute only 10-15%
total Ig in the serum.
Molecular weight of the IgA
is 385,000D.
The half life IgA in serum is
6 days.
It is the predominant Ig
class in exocrine secretion.
Two subclasses- IgA1and
IgA2.
4. IgA:
IgA1 and IgA2 both are heavily GLYCOSYLATED proteins.
IgA1 is the predominant IgA subclass found in serum.
Most lymphoid tissues have a IgA1 producing cells.
In IgA2 the heavy chains and light chains are linked with
noncovalent bonds.
Both IgA1 and IgA2 can be in membrane bound form.
5. Functions:
Provides local immunity.
It function is to protect the various exposed epithelial
elements of the body from invasion by pathogenic
microorganisms.
Secretory IgA present in breast milk protects new born
during first months of life.
It activates complement by alternative pathway.
7. IgM:
It is the first antibody are found early in every antibody
response,usually at low level.
IgM in mammals normally accounts to about 5-10% of
the serum IgS.
It has a half life for 6 days in serum.
The human IgM molecule is a pentamer made up of 5-
chain subunits each with a pair of heavy chains(μ) and
the pair of kappa(K) and lamda(λ) light chains.The μ
chain have about 130 amino acid residues.
8. IgM:
IgM have two ligand binding site but it looses its ability
to participate in agglutination and many other immune
reactions.
The IgM has one extra chain is called J chain.This chain
is 15,000D.
9. Functions:
Activation of classical pathway.
It cannot transverse blood vessels.It is restricted to the
blood stream.
It is a good complement activation of Ig.It is the most
effective in leading to the lysis of microorganisms.
It binds to the Fc receptors.
It act as opsonin.
11. IgD:
IgD is a glycoprotein produced as
a monomeric antibody with two
identical heavy chains and two
identical light chains.
It is found in very small amounts
in blood serum.
The molecular mass of IgD is
185kDa.
The half life of IgD is 2.8 days.
Its overall structure is same that of
IgG.
IgD molecules are relatively heat
labile and extremely sensitive to
proteases.
12. IgD:
IgD does not bind complement neither can cross the
placenta nor can bind the Fc receptor.
The light chains have two domains- one variable and
one constant.
The heavy chain have four domains- one varriable and
three constant region domains.
13. Functions:
In B cells the function of IgD is to signal the B cells to be
activated.Then B cells are ready to take part in the
defense of the body as part of the immune system.
