Uploaded April 2019 | Updated September 2026, 2 weeks ago

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This video is part 2 of Acquired immunity - Antibodies

Content
0:00 Introduction
0:06 Where do Antibodies Come From?
5:31 Components of an Antibody
7:32 Domains
8:37 IgG
9:50 IgM
11:53 IgA
13:39 IgD
14:22 IgE
15:17 Differences Between Antibodies
15:56 Table to Memorize

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All information in my immunology videos are from:
- Book: Immunology, Eighth Edition by David Male, Jonathan Brostoff, David Roth and Ivan Roitt
- Additional research in PubMed
- University lecture materials
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Antibodies: Plasma proteins

Where they come from:
1. B-cell (with BCR - IgG/D) bind to antigen
2. Present it on MHC II
3. APC activates a naive Th cell through TCR (CD4 and CD3), B7/CD28 and IL-4 receptor
4. Naive T helper cell secretes IL2 (autocrine)
5. Becomes an active Th2
6. Th2 helps active B-cell through CD40L/CD40 and T cell receptor.
7. IL-4, IL-5, IL-8, IL-10, IL-2, IFN gamma released depending on what type of antibody is needed.

Components of an Antibody:
Has:
Light Chain
Heavy Chain
Variable Part
Constant

Becomes:
VL, Vh, CL, Ch1, Ch2, Ch3

CL-Ch1 Connected through disulfide bonds
two parts of antibody connected through a Hinge which give the antibody motility

divided into Fab (fragment antigen binding) and Fc (Fragment crystalizable region)

Antibody Domains:
- Variable region - Antigen binding sites
- Ch1 region - Determine Allotype
- Ch2 region - Binds Complement
- Ch3 region - Binds Cells

Variants of chains:
Light Chain:
- Lambda Chain
- Kappa Chain
Heavy Chain:
- Gamma Chain (IgG)
- My Chain (IgM)
- Alpha Chain (IgA)
- Delta Chain (IgD)
- Epsilon Chain (IgE)

Functions of IgG:
- Exists as: Monomeric (plus subtypes)
- Amount in Plasma: 75%
- IgG is only antibody that pass through placenta. so we get igG from mothers.
- Direct Opsonization
- Activate Complement System
- IgG responsible for the secondary response in humoral immune response because memory B-cells are made to produce IgG

Functions of IgM:
- Pentameric (with a J-Chain) and Monomeric on B-cells
- ''Youngest Class'' since a fetus can produce them.
- IgM reacts as the primary response, but no memory as they are produced by T-cell independent B cell proliferation
- Complement activation

Functions of IgA:
- Dimeric (J-chain), Monomeric and Trimeric
- Found at mucosal entry
- Alpha plasma cells secretes IgA. IgA binds to epithelium through poly IgA receptors and transported through cytoplasm through endocytosis and sent out through proteolytic cleavage
- Many microorganisms can cleave IgA

Functions of IgD:
- Under 1% in blood
- Localized on surface of B-cells
- Monomeric

Functions of IgE:
- Very low amount in blood
- Monomeric
- Mast Cell
- Responsible for Type 1 hypersensitivity. Made after sensitization.
- Increase amount of IgE during allergic diseases and parasite infections.

Differences between Immunoglobulins:
- Idiotypic differences: Differ in variable region
- Isotypic Differences: Antibodies differ in constant region
- Allotypic Differences: Difference between alleles of same constant gene