BIO 343 Lecture Notes - Lecture 4: Immunogenicity, Antiserum, Fragment Crystallizable Region
Immunology Chapter 4: Adaptive Immunity
Hayden Casassa
• B Cell Reeptors BCR’s ad atiodies
o Specifically bind one or a limited number of extracellular antigens
o Antibody repertoire is the total number of different (1016) specific Abs that a person can make
▪ Number is actually closer to 109
o Stimulated B cell gives rise to antibody-secreting plasma cells with same Ag specificity as
original BCR
• Antibodies are glycoproteins with variable and constant regions
o Four polypeptides joined together by disulfide bonds.
o 2 heavy chains that are ~150 kDa and 2 light chains that are ~25 kDa each
o This leads to 2 identical Ag binding sites
o Greatest AA variability is between different Abs is in the N-terminal variable region
• Flexible hinge region of IgG allows binding to many different arrangements of antigens
o Following cleavage with a protease and a reducing agent, the Ab can be dissected into 3 pieces:
2 Fab fragments and 1 Fc fragment
o Stem of Ab is called the Fc region. Some cells express Fc receptors that bind this region (CD16 in
ADCC on NK cells)
• 5 Isotypes or Classes of Human Antibodies by differences in heavy chain region
o gamma (g), mu (m), delta (d), alpha (a), and epsilon (e) chains
• Light chains either have Kappa (k) or lambda chains
• All 5 antibody types could bind to the same pathogen, but once it binds how that it is dealt with differs
on type of antibody that it is bound to.
find more resources at oneclass.com
find more resources at oneclass.com
o IgG can be passed to offspring through bloodstream
o IgE can bind to mast cells due to constant region
• Heavy and light chain are folded into series of compact and stable Immunoglobulin (Ig) domains
o There are 12 domains of IgG
▪ 3 Constant domains and 1 variable region for each heavy chain
▪ The light chain has 1 variable and 1 constant region
▪ Annotated VH→CH1→CH2→CH3 or VL and CL
▪ Each domain consists of 2 Beta-pleated sheets
• Be able to name domains of antigen binding site or whole IgG molecule
• Immunoglobulin Superfamily
o Large group of cell surface and soluble proteins that contain one or more Ig-like domains
• Antigen Binding Site
o One Ag binding site consists of hypervariable regions (HVs) also known as Complementarity-
Determining Regions (CDRs) present in the six loops from the VH and VL domain
o 3 loops in each CDR for the 4 variable regions meaning 12 Variable regions in every Antibody
▪ 6 per antigen binding site
▪ The loops are’t idetial
o Framework region has little difference (Yellow), but the Red HV region is where the Ag binds
• An antigen is any molecule that can be bound by a B cell receptor (BCR) or antibody, or by the T cell
receptor (TCR) when it is complexed with and MHC molecule
o TCR’s ol reogize peptide fragets of protei Ags that hae ee degraded ad displaed
by other cells expressing MHC molecules
▪ In other words, only way T cell can recognize is when a human cell when the fragment is
attached to MHC molecule
• Immunogenicity is the ability of a substance to induce a B cell and/or T cell adaptive response.
o Typically, the bigger and more diverse then the better they elicit an immune response
o AA (worst)→ Haptens→ Lipids→ Steroids→ Carbs→Proteins (best)
• Properties of Immunogens and Antigens (What makes a good antigen)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
2 fab fragments and 1 fc fragment: stem of ab is called the fc region. Some cells express fc receptors that bind this region (cd16 in. Igg can be passed to offspring through bloodstream. Immunoglobulin superfamily: large group of cell surface and soluble proteins that contain one or more ig-like domains, antigen binding site, one ag binding site consists of hypervariable regions (hvs) also known as complementarity- In other words, only way t cell can recognize is when a human cell when the fragment is attached to mhc molecule. Good: humanized are entirely human with only the hv region (cdr) being of mouse origin. Best: antibodies are encoded by gene segments spread along chromosomes, they are brought together randomly to form a rearranged functional gene by somatic. Recombination: somatic recombination occurs only during b cell development in the bone marrow before.
