Types of Antigens - - Infection(bad foreign)
- gut flora(good foreign)
- cancer(bad self)
- autoimmunity(good self)
what's recognizes antigens? - - adaptive immune system
- innate only can recongize PAMPS
what are antigens? - - molecule that can interact(specifically) w immunoglobulin(Ig)...
MDSC 321 Second Midterm 2024
Types of Antigens - - Infection(bad foreign)
- gut flora(good foreign)
- cancer(bad self)
- autoimmunity(good self)
what's recognizes antigens? - - adaptive immune system
- innate only can recongize PAMPS
what are antigens? - - molecule that can interact(specifically) w
immunoglobulin(Ig) receptor of B cells(or T cell receptor complexed w MHC)
- cells see it
immunogen - - molecule that induces specific immune response
- all immunogens are antigens
- not all antigens are immunogens
- in a western blot detected by antibodies, there are only antigens and no
immunogens because no immune response
- a ligand for B cells in vivo would be antigen and immunogen because response
can be initiated
humoral immunogens - - B cells
- proteins>polysaccahrides> lipids/nucleic acid
cells mediated immunogens - - T cells
,- proteins, some lipids, some glycolipids
- slow and picky
- need help
- proteins not recognized directly
- processed peptides from protein seen in association w MHC molecules, lipids w
an MHC-like molecule CD1
what are the 4 properties of an immunogen? - - foreigness
- molecular size
- chemical heterogeneity
- degradability
foreigness - - to be an immunogen, molecule must be seen as non self
- degree of immunogenicity depends on degree of foreigness
- greater the phylogenetic distance btw species typically greater chance of
immunogenicity
- eg. bovine serum albumin injected into chickens/goats
what are exceptions of the foreigness property of an immunogen? - - highly
conserved molecules like collogen or cytochrome c may not be immunogenic even
in distant species
- some self molecules, normally sequestered from immune system, will raise an
immune response(eg. sperm or lens tissue) in animal they come from
molecular size - - correlation btw size and immunogenicity
- best immunogens in the range of 100,000 Da
- small molecules 5-10, 000 Da generally poor immunogens
,- need to be large enough to be processed
chemical heterogeneity - - size alone doesn't make good immunogen
- synthetic homopolymers not immunogenic regardless of size
- large co-polymers can be immunogenic and adding aromatic amino acids
increases the chance
- proteins w higher complexity in primary structure and those showing secondary,
tertiary and quaternary structure increase immunogenicity
degradability - - protein degraded to be presented by MHC molecules to activate T
cells
- factors influencing this process affect immunogenicity
- insoluble>soluble bc more likely to be phago. and processed
- large>small (more processing and more epitopes)
- L amino acids>D amino acids(works w processing enzymes
how can we make an antigen more immunogenic? - adjuvants
adjuvants - - change envir. for better response
- to help
- substance that when injected w Ag, it enhances immunogenicity of Ag
- resulting in higher antibody titer and longer lasting immune response
- not specific to an antigen but can be used w many diff. antigens
, - freund's complete adjuvant, containing muramyl dipeptides from cell walls of
heat killed myobacteria stimulate macrophage activity
- increase in IL-1 helps activate helper T cells
- synthetic polyribonucleotides and baterial LPS stimulates non specific
lymphocyte proliferation
- some stimulate local chronic inflammation and granuloma formation(freund's
complete)
adjuvant mechanism step 2 - - prolong exposure to Ag
- alum and freund's adjuvant bind and precipitate Ag to keep in system longer and
allow for slow realease of Ag
- increase time of exposure from few days to few weeks
- precipitation increases size of Ag to facilitate phago.
adjuvant mechanism step 3 - - co stimulatory signal
- helper T cells when stimulated by Ag need second co stimululatory signal
- freud's adjuvant, LPS and other factors up regulate co stimulatory signal systems
epitopes - - lymphocytes dont recognize entire antigens
- they recognize small discrete sites on macromolecules called antigenic
determinants or epitopes
- epitopes seen by b cells and t cells differ in many diff ways
- antibodies see diff spots of epitopes
B cell epitopes - - b cells bind Ag directly via cell surface immunoglobulin(Ig)
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