[DISCUSSION] MODULE 1 UNIT 2 Flashcards
•Refers to a substance that reacts with antibody or
sensitized T cells
ANTIGEN
•May not be able to evoke an immune response in
the first pla
ANTIGEN
•Macromolecules capable of triggering an
adaptive immune response by inducing the
formation of antibodies or sensitized T cells
•IMMUNOGENS:
“ALL (?) ARE ANTIGENS, BUT NOT ALL
(?) ARE IMMUNOGENS.”
IMMUNOGENSANTIGENS
• Induce detectable specific immune responses
IMMUGENECITY
• Results to formation of antibodies (humoral
immune response) and activation of T
lymphocytes (cellular/cell-mediated immune
response)
IMMUNOGENICITY
• Ability to react with the specific antibodies or
activated T cells that it induces
SPECIFIC REACTIVITY/ ANTIGENICITY
•Partial or incomplete antigen
HAPTENS
•Small, chemically defined substances which
are not immunogenic but can react with
antibodies of appropriate specificity
HAPTENS
•Usually a small molecule; thus cannot be
immunogenic
HAPTENS
•If it is conjugated with protein, it becomes a
bigger molecule, and it becomes
immunogenic
HAPTENS
• Immunologically active portions of an antigen
which can react with antibodies and T-cell
antigen receptors (after antigen processing)
EPITOPE (ANTIGENIC DETERMINANT)
• Involved with actual binding
EPITOPE (ANTIGENIC DETERMINANT)
• Can be linear or conformational
EPITOPE (ANTIGENIC DETERMINANT)
→ consist of sequential amino acids on
a single polypeptide chain
• Linear
→ result from the folding of a
polypeptide chain/s, and nonsequential amino
acids are brought into close proximity
.• Conformational
• Provides bulk or molecular mass to the antigen (Ag)
molecule
CARRIER /SCHLEPPER MOLECULE
• May be albumin, globulin or synthetic polypeptide
CARRIER /SCHLEPPER MOLECULE
CARRIER /SCHLEPPER MOLECULE SIGNIFICANCE:
Adds bulk so it becomes immunogenic
Important in regulation of humoral immune
response to the Ag
HBsAg added with carrier molecule (yeast)
→
vaccine
→ recognize the carrier portion
• T cells
→ recognize the haptenic portion
• B cells
•ANTIGEN MOLECULES MAY BE:
- Univalent and unideterminant
- Multivalent and unideterminant
- Multivalent and multideterminant
•Nonself component of the host ; alien to the host
FOREIGNESS
•Generally, only foreign substance is immunogenic
FOREIGNESS
• Substances that are altered from what is normal
to the host may become immunogenic →
autoantigen
Foreigness
• E.g., in cancer cells →
production of tumor specific antigen
• Heterogeneity in the building blocks that make up the
antigen
CHEMICAL COMPLEXITY
• Chemically complex
• Most immunogenic
PROTEINS
• Building blocks are repeating monosaccharide units
POLYSACCHARIDES
• Weak and partial immunogens
POLYSACCHARIDES
do not possess sufficient chemical diversity
POLYSACCHARIDES
- rapidly degraded
POLYSACCHARIDES
•Immunogenic forms of polysaccharides
- Pure polysaccharides
- Lipopolysaccharides
- Pure polysaccharides
• Pneumococcal capsule
- Lipopolysaccharides
• Endotoxins of gram-negative bacteria
• Strong immunogens
GLYCOPROTEINS
• ABO blood group antigens
GLYCOPROTEINS
•Usually weak immunogens
•POLYPEPTIDES
•POLYPEPTIDES examples
hormones: insulin and growth hormone
•in the form of DNA and RNA
•NUCLEIC ACIDS
•Usually not immunogenic, unless coupled to a
protein
•NUCLEIC ACIDS
•In some autoimmune disorders like SLE, tjese are are immunogenic (anti-ds-DNA are formed)
•NUCLEIC ACIDS
•Include triglycerides and other fatty substances
LIPIDS
•Not immunogenic unless coupled to proteins
LIPIDS
• E.g., cardiolipin used in the RPR tes
LIPIDS
• The larger the molecule the better immunogen
HIGH MOLECULAR MASS/ SIZE
• Molecules less than 1 kD →
non immunogenic
• Molecules > 1 kD but <6kD →
weakly
immunogenic
• Molecules > 10kD →
more immunogenic
•Reasons why size/mass is important in
immunogenicity:
•Number of epitopes increases proportionately
with size
• Large size of molecules become easily phagocytosed and processed by macrophages to become more attractive to T cells
Tertiary conformational structure of the protein molecule
SPATIAL ACCESSIBILITY OF DETERMINANT GROUPS
•Must be exposed and accessible to the receptors of immunoglobulins or the T cell receptors (TCRs)
SPATIAL ACCESSIBILITY OF DETERMINANT GROUPS
•Must be exposed and accessible to the receptors of immunoglobulins or the T cell receptors (TCRs)
→
so the antigen can be bound
•Hidden (internally located) determinant groups
→
NOT REACTED UPON