ImmunologyChapter 5, Lecture 2

• Richard L. Myers, Ph.D.

• Department of Biology

• Southwest Missouri State

• Temple Hall 227

• Telephone: 417-836-5307

• Email: rlm967f@mail.smsu.edu

• 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)