Antigens, Immunogens, Epitopes, and Haptens. Innate and adaptive immunity:
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Transcript of Antigens, Immunogens, Epitopes, and Haptens. Innate and adaptive immunity:
Antigens, Immunogens , Epitopes, and Haptens
Innate and adaptive immunity:
Innate (Natural) Immunity:
Inborn resistance.present the first time a pathogen is encountered (does not require prior exposure)
Usually not specificnot modified by repeated exposure to the pathogen.
Adaptive (Acquired) Immunity:
weak or absent at the first exposure.
specific increases dramatically with subsequent exposures to the same pathogen (Memory)
•Types of innate immunity:Humoral (soluble)immunityCell mediated immunity
• Types of adaptive immunity Humoral (soluble)immunity Cell mediated immunity
Soluble mediators of innate immunity:
•Proteins and enzymes•Cytokines & type 1 interferons.•Complement
Proteins and enzymes
oA variety of proteins and enzymes (present in human blood and tissue fluids) are considered the first part of innate immunity.oExample: C reactive protein (CRP), lysozymes, and defensins.
nCytokines, and Type I interferons:
Cytokines: IL-1, IL-6, IL-12, and TNFα produced by activated phagocytes.
Type I interferons:
oIFN- α produced by dendritic cells
oIFN-β Produced by fibroblasts.
-INFs are rapidly produced, within minutes by
the infected cells (virus infection).
Cells of Innate immunity:
• Phagocytes:
- Monocytes and macrophages: blood
stream and tissues.
- Dendritic cells: lung, and GIT mucosa.
•Granular leukocytes:
-Neutrophils, and eosinophils.
-Basophils and mast cells.• Natural killer cells (NK).
Adaptive Immunity:
• Soluble mediators of adaptive immunity:
- Cytokines: IL-2, IL-3, IL-10,IL-13.
- Interferons: INF-γ (Gamma).
- Complement.• Soluble and cell-bounded proteins:
-The Immunoglobulins.
• Immune cells:
- T lymphocytes
- B lymphocytes
- N.K cells.
• n
Phagocytes: monocytes, MQ & DC
Granular leukocytes
Cytokines: IL1, IL6, IL12 & TNFα.
Interferons: IFα and IFβ.
T lymphocyte & B lymphocytes
Cytokines: IL2, IL3, IL10 & IL13.Interferons: IFγImmunoglobulins.
Complement
NK cell
n
Antigens, Immunogens , Epitopes, and Haptens
Antigen:
Is a molecule or part of a molecule that is recognized by the immune system.
Immunogen:
Is an antigen that evokes a specific, positive immune response.
Example:
Injecting a laboratory animal by human
chromosome Anti-DNA
antibodies and anti-Histons Antibodies
will be produced.
Immunogenicity and Properties of immunogen:
Immunogenicity is the ability of immunogen to activate immune response.
Properties of Immunogen:o Foreignnesso Sizeo chemical nature and complexity.
•Foreignness:
Immune system can discriminate between foreign and self substance (self & non self)•Size:
Molecular weight of at least 10,000 Dalton. •Chemical nature:
-Mainly proteins (polypeptide)
-Carbohydrates, steroids, and lipids are poor immunogens.
nChemical complexity:
As the chemical complexity increases; the
immunogenicity increases.
Homopolymers are poor immunogens
regardless of size, while heteropolymers
are strong immunogens.
Proteins are heteropolymers (different
amino acids)
n
Epitopes
(The Antigenic determinants): The smallest part of an antigen or immunogen that can be recognized by the B & T cells receptors. So it is the basic recognition element.
A single antigen molecule may have several different epitopes.
Immunodominant epitope is an epitope that can stimulate a greater antibody response than others.
• N
epitopes
•B cell receptors can recognize epitopes whether they are:
free soluble molecules. Surface-bound molecules. Degraded fragments.
•T cell receptors can bind only to epitopes which are surface-bound molecules.
Superantigen:
• is a substance such as a bacterial
toxin that is capable of stimulating
multiple T lymphocytes, leading to
release of relatively large quantities of
cytokines.
n
Hapten:
Small, non-biologic molecules that bind
to immune cells receptors but cannot
by themselves induce a specific
immune response.
(Land-Steiner’s experiment).
Injected a mice with:
• hapten No immune
response• carrier (protein) Anti carrier
•Hapten + Carrier Anti-Hapten +
Anti-Carrier
T-cell dependent and T-cell independent Antigens:
•Antigens are classified as either T-cell dependent or T-cell independent.
•T cell dependent antigen activates immune system depending on T-lymphocytes.
T-cell dependent antigen
T-cell independent Antigen
Structural properties Complex Simple
Chemical nature Proteins, glycoprotein, and lipoproteins
Polysaccharide; bacterial
Lipopolysaccharide.
Antibody - class induced
IgG, IgM, IgA, IgD, and IgE
Only IgM
Immunological Memory
yes No
Present in most Pathogens
yes No