The document summarizes key aspects of immunoglobulins (antibodies): - Antibodies are large Y-shaped glycoproteins produced by plasma cells that bind specifically to antigens. There are five classes of human antibodies that share a basic structure but vary to perform specific functions. - Antibody molecules contain two identical heavy chains and two identical light chains. Light chains can be kappa or lambda type. The variable regions of the heavy and light chains give antibodies their antigen specificity. - Each antibody contains two antigen binding fragment (Fab) regions and one crystallizable fragment (Fc) region. The Fab binds antigens while the Fc mediates immune responses through binding to other immune molecules and cell receptors.

1. Immunology
By
Ahmed Riyadh Abdul Rahman
Al-Noor University College
1

2.  An antibody or immunoglobulin (Ig) is is a large, Y-shaped a glycoprotein
produced mainly by plasma cells.
 Immunoglobulins bind specifically to antigens which stimulated their
formation.
 The Igs are present at different body sites including serum, blood, extra-
cellular fluid, CSF, saliva, tears, exocrine secretions (nasal, intestinal &
breast milk), and on surface of lymphocytes.
 There are five classes of human antibodies; all share a basic structure that
varies in order to accomplish specific biological functions.
2

3. Light Chains
Studies of Ig from many species showed that nearly all species studied had two types
of Light chains, called:
 kappa (κ) and
 lambda( λ).
• The difference between the two types of light chains is in the amino acid sequence of the
constant (C) region domain of the chain, In humans, the constant regions of all light
chains are identical.
• Each antibody molecule produced by a sole B cell will contain either kappa (κ) or
lambda ( λ) light chains but never both, light chain has two domains: one constant
domain and one variable domain.
3

4. 4
 Each light chain and each
heavy chain has 2 end, the
amino-terminal (N-
terminal) at the variable
region and the carboxy
(COO-) terminal (C-
terminal) at the constant
region which are importat
for the Igs biological
activity.

5. Variable & Constant Region or Domains
1. Variable (V) Domains
• The domains located at the amino-terminal have variable (different) A.A sequences
between the various antibody molecules. In each monomer, there is one V domain in the H
chain (VH) and one V domain in the L chain (VL). The V domains of both the H & L
chains determine the specificity of the antibody molecule.
• Variable regions show greatest variability in sequence in Light and Heavy chains, these
were called hypervariable regions (greater specificities); regions that differ extensively
and represent amino acid sequences that are unique to a particular antibody and
complementary to a particular antigenic epitope. Hence hypervariable regions are also
termed complementary determining regions (CDRs), these regions are essential in
determining antigen specificity.
• Hypervariable regions of VH and VL domains form the antigen-combining (binding) site
(paratope).5

6. 2. Constant (C)
• All domains, except the V, have constant A.A. sequences. The L chain has only
one C domain (CL), but the H chain has 3 or 4 C domains (CH1, CH2, CH3 &
CH4). These C domains are located toward the carboxyl (COO-) terminal of
the monomer.
6

7. Antibody Fab and Fc Regions
1-Fab (fragment, antigen binding) region
• The arms of the Y consists of two Fab (antigen-binding fragments), this
region of the antibody is called the Fab region for "fragment antigen
binding"(also known as paratope), and is the part of the antibody that
binds to antigens. This is also where the variable amino acid sequences
occur. It is composed of one constant and one variable domain from
each heavy and light chain of the antibody.
7

8. 2-Fc (Fragment, crystallizable) region
• The base (stalk) of the Y called the Fc (Fragment, crystallizable) region (named because its
observed to crystallize readily), and is composed of two heavy chains that contribute two or
three constant domains depending on the class of the antibody. its plays a role in modulating
immune cell activity By binding to specific proteins, The Fc region play a importat role in
binding of the Abs to the surface of cells these antibody called A cytophilic antibody (also
named cytotropic antibody or anaphylactic antibody) is a type of antibody that has an affinity
for certain kinds of cells, in addition to and unrelated to its specific affinity for the antigen that
induced it, because of the properties of the Fc portion of the heavy chain.
• The Fc region also binds to various cell receptors, such as Fc receptors, and other immune
molecules, such as complement proteins. By doing so, it mediates different physiological effects
including opsonization, cell lysis (Complement activation, Complement fixation), and
degranulation of mast cells (hypersensitivity), basophils and eosinophils and placenta crosses.
8

9. The immunoglobulin hinge (interdomain) region
• The hinge region is a flexible amino acid stretch in the central part of the heavy chains
(between the CH1 and CH2 domains) of the IgG and IgA, IgD classes, which links
these 2 chains by disulfide bonds. It is rich in cysteine and proline amino acids,
extremely variable in amino acid sequence, and has no resemblance to any other
immunoglobulin region.
• The hinge region permits flexibility between the two Fab arms and the Fc part of the
antibody, this flexibility is an important feature of antibody structure ,allowing
interaction with antigens and effector molecules in a variety of environments.
9

10. 10

11. Basic Structure of antibody
Monomer: This is the basic structure of the antibody. It is composed of 2 pairs of
identical polypeptide chains, the Heavy chains (H), and the Light chains (L). are joined
together by disulfide bonds (S-S).
Polymers: are composed of more than one monomer; 2 monomers= Dimer, 3=
Trimer, 4= Teramer, 5= Pentamer, 6= Hexamer. Examples: IgM in the serum is
usually pentamer and rarely hexamer, while on lymphocyte surface is monomer. Also,
secretory IgA (IgA2 in exocrine secretions) is usually dimer and sometimes trimer,
while in the serum is monomer.
11

12. 12

13. THANK
YOU
13