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a. Same antigenic determinants repeated
several times, b. T. dependent antigen, they have few copies of many different
antigenic determinants, C. Hapten carriers.
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Immunogenicity is the ability of an antigen or
epitope to produce immune response to foreign cells in human and
animals.
Antigen
(ag),
is any substance that evolves immune response when it comes in contact with
appropriate cells after a latent period and also react with antibodies. It is
any substance that provokes the lymphoid tissue to respond by generating an
immune reaction specifically targeted at an inducing substances only.
Epitope
or antigenic determinant, is that part
of an antigen that combines with the product of a specific immune response.
There are two types of
immunogenicity.
A. Wanted
Immunogenicity: this type of immunogenicity is parts of the adaptive or nonspecific immunity, as it involve vaccines (therapies), they are administered to provoke
immune response thereby protecting the body.
B. unwanted
Immunogenicity: This is the innate component of immunogenicity, it involve the
response of the body on its own against an antigen. It results in the
production of ANTI DRUG ANTIBODY (ADA), this then inactivates the effect of a
drug or vaccine (treatment) thereby reducing side effect.
A. Contribution of the Immunogen
1. Foreignness:
The immune system normally discriminates between self and non-self Such that only
foreign molecules are immunogenic.
2. Size:
There is not absolute size above which a substance will be immunogenic. However,
in general, the larger the molecule the more immunogenic it is likely to be.
3. Chemical
Composition: Larger molecules are naturally more immunogenic, and the more
complex the substance is chemically the More immunogenic it will be. The antigenic determinant are created by the
primary Sequence of residues in the polymer and or by the secondary, tertiary
or quaternary.
Structure
of the Molecule
4. Physical
form: Particulate antigens are more immunogenic than soluble ones and
denature antigens more immunogenic than the native form.
5. Degradability: Antigens
that are easily phagocytosed are generally more immunogenic, this is best
explained as follow, most antigens, T-dependant antigens, requires that the
antigen be phagocytosed, processed and presented to helper T cells by an
antigen presenting cell [APC].
B. Contribution
of the biological system
1. Genetic
Factors: Some substances are immunogenic in one species but not another. Similarly,
some substances are immunogenic in some individual but not in others [i.e.
responders and non-responders]. The
species or individuals may lack or have altered genes that code for the
receptors for antigen on B cells and T cells or they may not have the
appropriate genes needed for the APC to present antigen to the helper T cells.
2. Age: Age can also influence
immunogenicity. Usually very young and
the very old have a reduced ability to mount an immune response to an
immunogen.
C. Method
of administration
1. Dose:
Dose of administration also affects immunogenicity, there is a dose of antigen above
or below which the immune response will not be optimal.
2. Route:
Route of administration like other factors also affects immunogen; in general,
the subcutaneous route is better than the intravenous or intragastric
routes. The route of antigen administration
can also affect the nature of response
3. Adjuvants:
these are Substances that enhances the
immune response to an immunogen. Their
use is limited because of side effect which they produce in the individual.
Chemical nature of immunogen
Proteins:
Immunogen are mostly proteins, others are glycoprotein or lipoproteins. Other
they are polysaccharides, and lipids. nucleic acids are also good immunogen
when they occur in single strands; the double stranded forms are very poor.
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