The document discusses the structure and classes of antibodies (immunoglobulins). It notes that antibodies have a Y-shaped structure consisting of two heavy chains and two light chains. The heavy chains have four or five constant domains, while the light chains have two domains. There are five classes of antibodies - IgM, IgG, IgA, IgD, and IgE - which differ in structure and function. IgG is the most abundant antibody and can cross the placenta, while IgM is the first antibody produced against new pathogens. IgA is found in secretions and protects mucosal surfaces.

1. Immunoglobuli
n's
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2. Antibody structure
 The other domain is called Constant region
domain because they do not differ to the same
extent from antibody to antibody. The heavy chain
constant region are CH1, CH2, CH3, CH4 while
the light chain domain is CL. Between CH1 and
CH2 domains of the heavy chain, we have hinge
region which contains Prolines which makes part
of the molecule more flexible.
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3. Learning objectives
 To understand the cells of specific immune
system.
 To learn that antibodies are molecules of
specific immunities
 To understand how antibodies recognize their
foreign molecules on pathogenic organism
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4. Introduction
 After infection, the first encounter between the
pathogen and the infected individual is through
the innate immune system, which on major
occasion result in an inflammatory responses in
our body system. Immunoglobulin's are also
called antibodies. The antibodies are glycoprotein
that have the ability and capacity to recognize
foreign molecules on the surface of a pathogens.
They are specific in nature.
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5. Antigenic properties of antibody

6. Antibody structure
 The basic structure of antibodies is depicted as Y-
structure consisting of four protein subunits. The
structure of immunoglobulin's are divided into Heavy
chains(H) and light(L) chains. The heavy chains have a
molecular weight of 50-75kDa. The light chains have a
molecular mass of about 25kDa. There are two types of
light chains kappa(k) and lambda(A). An individual
immunoglobulin's will contain two Heavy chains and
two types of light chain (kappa or lambda). The heavy
chains are linked together and with the light chain by a
disulphide bridges.

7. Structure of an antibody

8. Antibody Structure

9. Antibody structure
 The structure of heavy and light chains of
immunoglobulin's have a domains. The domains are
region of repeating regions with approximately about
110 amino acids inked by a disulphide bridges. The
heavy chain of immunoglobulin's has four or five(4 or
5) domains and the light chain has two. The domains at
the N-terminal ends of the heavy and light chains are
referred to as Variable domains(Vh and Vl respectively)
because the amino acid sequence of this region are
found to differ from one antibody to the other.

10. Recognition by antibody
 Usually antibodies binds to molecules that are
foreign to the body. These molecules may be on
the surface of pathogen or they are secreted as
toxins by the pathogens. The molecules that the
antibody binds are called antigens. The antigens
could be protein, carbohydrate or lipids. The
antibody does not bind to the whole of an antigen;
it binds to the part of the antigen called “antigenic
epitope”

11. The nature of antibody-antigen
binding
 The chemical interactions that occur between
antibody and antigen is a non-covalent type of
bonding. This bonding include, Van der waals
force, hydrophobic interaction, hydrogen bond
and electrostatic interaction. The strength with
which the antigen-binding site of an antibody
binds to an antigenic epitope is called “affinity”
of the antibody for the antigen.

12. Affinity and avidity of antibody-
antigen interactions
 Antibodies have at least two antigen binding
sites , which is made up of heavy chain/light chain
pair of polypeptides. The strength with which an
individual binding site of an antibody binds its
epitope is called affinity of binding. However, if an
antibody is using both binding sites to bind to two
epitopes on the same particle, the overall strength
of the binding is increased and the total strength
of this binding is referred to as “avidity” of the
antibody for the antigen.

13. Antibody Classes
 Antibodies binds to the particle by specifically binding
to antigens on the surface of the particle, which could
be bacterium or virus. Phagocytes have receptors ,
called Fc receptors(FcRs), on their cell surface that can
bind to the Fc portion of antibody molecules that have
bound antigen. There are five different classes of
antibody in humans;IgM, IgG, IgA, IgD and IgE. Slightly
different variations of IgG and IgA exist , which are
referred to as subclasses of antibody. There are four
subclasses of IgG and two subclasses of IgA.

14. Immunoglobulin G (IgG)
 This is the most abundant antibody in serum and
exist as the basic 2H + 2L chain antibody
molecule. The four subclasses of IgG are IgG1,
IgG2, IgG3, and IgG4. All is having 2 heavy + 2
light chain structure. This is the only
immunoglobulin that has the ability and capacity to
cross the placenta blood barrier of the mother to
the baby so as to confer immunity to the new
born. IgG is the most abundant immunoglobulin's,
about 80%.

15. Immunoglobulin G (IgG)

16. Immunoglobulin G (IgG)

17. Immunoglobulin M (IgM)
 IgM is the earliest antibody to be produced
after first contact with a new antigenic
pathogen. It is a pentamer structurally with
five Immunoglobulin's molecules joined
together by a disulphide bonds and an extra
protein called J-chain. The H-chains of Igm
differ from those of IgG in having four
constant domains instead of three of IgG. In
abundance, IgM is about 5-10%.

18. Immunoglobulin M (IgM)

19. Immunoglobulin A (IgA)
 This immunoglobulin is present in the serum and also class of
antibody found in various secretions such as mucus in the
intestinal and respiratory tracts, saliva, sweat, breast milk and
colostrum. The two subclasses of IgA in the human are IgA1 and
IGA2, appear to have the same functions. IgA has different
structures depending on whether it is in serum or secretions. In
serum, IgA has a basic 2 heavy + 2 light chain Immunoglobulin
structure. IgA in secretions has a different structure and consists
of two Immunoglobulin molecule joined together by a J-chain and
an additional protein called the secretory piece. The secretory
piece helps the transport of IgA into secretions and also help to
protect the IgA from being broken down by proteolytic enzymes
that are present in the bodily secretions.

20. Immunoglobulin E (IgE)
 This present at the lowest concentration of a
antibody classes in serum. It exists as a
monomer consisting of the basic two heavy
and two light chain Immunoglobulin structure.
It has four C-domains. It has a very important
functions that is involved in asthma and
allergic reactions in the body.

21. Immunoglobulin (IgD)
 It is very low in the blood plasma(less than
0.1%).
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22. Secretion and expression of
antibody on cell surface of B
lymphocytes
 The cells that make antibody are called
plasma cells. They are derived from type of
white blood cell called B- lymphocytes. The B-
lymphocytes themselves are produced from
the bone marrow and then circulate through
the blood stream, spleen, lymph nodes and
other lymphoid tissue.

23. Clinical correlates
 1. Bruton Disease(X-inked agammaglobulinemia), is
an inherited immunodeficiency disease caused by
mutations in the gene coding for Bruton tyrosine
kinase. Bruton tyrosine kinase is essential to the
maturation of pre-B cells to differentiating to mature B-
cell. It is very rare disorders affecting males. Females
may be a carrier but has no clinical manifestations. This
usually present with following symptoms: recurrent
infections, chronic rhinitis and growth chart may show
evidence of failure to thrive. The management of this
patient is to give Intravenous immunoglobulin.

24. Clinical correlates
 2. Selective immunoglobulin A(IgA) deficiency: it is
a genetically associated immunodeficiency which
is a type of hypogammaglobulinemia. People with
this disease can not synthesize IgA which protect
our genera mucous membranes of the respiratory
system, gastrointestinal system. In about 80% of
patient, it is asymptomatic. Some affect patients
tend to present with sinupulmonary infections,
allergies and autoimmune conditions. Treatment is
with antibiotics for the underlying infections.

25. End of lecture
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