An updated view of Immunoglobulins and Acquired Immunity (good for a compact overnight exam preparation)

1. Immunoglobulins
Aindrila Saha
Fig: Schematic diagram of structure of
immunoglobulins derived from amino acid sequencing
studies. Each heavy and light chain in an
immunoglobulin molecule contains an amino-terminal
variable (V) region (aqua and tan, respectively) that
consists of 100– 110 amino acids and differs from one
antibody to the next. The remainder of each chain in
the molecule—the constant (C) regions (purple and
red)—exhibits limited variation that defines the two
light-chain subtypes and the five heavy-chain
subclasses. Some heavy chains also contain a
proline-rich hinge region (black). The amino-terminal
portions, corresponding to the V regions, bind to
antigen; effector functions are mediated by the other
domains. The light and heavy chains, which lack a
hinge region, contain an additional domain in the
middle of the molecule.

2. Fig: Ig classes from Kuby, 6th edition

3. Functions:
1. Antigen binding
2. Opsonization
3. Activation of complement pathway
4. Antibody dependent cell mediated cytotoxicity
5. Crossing the epithelial layer by transcytosis

4. Ig superfamily
1) Ig-alpha/Ig-beta heterodimer, part of the B-cell
receptor
2) Poly-Ig receptor, which contributes the
secretory component to secretory IgA and IgM
3) T-cell receptor
4) T-cell accessory proteins, including CD2,
CD4, CD8, CD28, and the gamma, delta and
epsilon chains of CD3
5) Class I and class II MHC molecules
6) beta 2 -microglobulin, an invariant protein
associated with class I MHC molecules
7) Various cell-adhesion molecules, including
VCAM-1, ICAM-1, ICAM-2, and LFA-3
8) Platelet-derived growth factor
Fig: A. Basic structure of Ig superfamily proteins and
B. Evolution of genes of Ig superfamily.

5. Antibody Diversification
1. Multiple germ-line gene segments
2. Combinatorial V-(D)-J joining
3. Junctional flexibility
4. P-region nucleotide addition
(P-addition)
5. N-region nucleotide addition
(N-addition)
6. Somatic hypermutation
7. Combinatorial association of light
and heavy chains
Fig: Experimental evidence for somatic mutation in
variable regions of immunoglobulin genes (Kuby,
5th edition)