ImmunologyChapter 5, Lecture 2
• Richard L. Myers, Ph.D.
• Department of Biology
• Southwest Missouri State
• Temple Hall 227
• Telephone: 417-836-5307
• Email: [email protected]
• Homepage: http://creative.smsu.edu/biology/myersr/index.html
• TopClass: http://creative.smsu.edu
Immunoglobulin receptor
• Membrane-bound antibody (mIg) on B cell determines B cell specificity
• Secreted antibody (sIg) differs in the carboxyl-terminal domain
• mIg has three additional regions– extracellular hydrophilic sequence– hydrophobic transmembrane sequence– short cytoplasmic sequence Ig
mIg
• All five Ig classes can be expressed as mIg– occurs at different developmental stages
• immature cell expresses only sIgM
• mIgD appears later in maturation
• memory cells express a variety of isotypes
• Genetic mechanisms are responsible for expression of a particular mIg
• B cell receptor indicated by BCR
BCR
• The tail of the BCR is too short to signal– through tyrosine kinases and G proteins
• Recently shown that BCR has other parts– a heterodimer called Ig-/Ig-– two molecules associate with one mIg– both Ig- and Ig- have long cytoplasmic tails– both contain tyrosine residues that can be
phosphorylated by tyrosine kinases
Antigenic determinants on Ig
• Antibodies are glycoproteins
• Therefore, will serve as immunogens
• Epitopes on the Ig fall into three categories:– isotypic– allotypic– idiotypic
• Epitopes located in characteristic positions
Immunoglobulin isotypes• IgG
– most abundant type
• IgM– pentamer
• IgA– secretory Ig
• IgE– causes hypersensitivity
• IgD
Immunoglobulin superfamily
• Heavy and light chains share characteristics
• Common evolutionary ancestry possible?– all have the immunoglobulin-fold domain– perhaps the genes encoding them arose from a
common primordial gene
• Many membrane proteins have structures similar; did they come from the same gene?
• Classified as immunoglobulin superfamily
Members of the superfamily
• Part of the BCR
• Poly-Ig receptor (for secretion)
• T-cell receptor
• CD2, CD4, CD8, CD 28 and part of CD3
• Class I and II molecules
• Cell-adhesion molecules
• Others
Monoclonal antibodies
• Produced by fusing an antibody-producing plasma cell with a myeloma cell– produces a hybridoma– possess immortal character of the myeloma– and the antibody-synthesizing capacity of the B
cell
Assignment
• Read Chapter 6, Antigen-Antibody Interactions
• Review question 6 (pg 163)
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