After looking at the immunoglobulin heavy chain gene structure in detail, the goal of this section will be to review key points about the heavy chain and, then, compare them to the light chain.
Ig Heavy Chain Gene:
- Contains separate gene segments for the Variable (V), Diversity (D), and Joining (J) regions
- Multiple germline V, D, and J gene segments are present
- V(D)J recombination during B cell development rearranges one V, D, and J segment
- Constant (C) region is encoded by separate C exons (Cμ, Cδ, Cγ, Cα, Cε)
- Multiple different C region isotypes allow class switching (IgM, IgD, IgG, IgA, IgE)
Ig Light Chain Genes (Kappa and Lambda):
- Only contain separate gene segments for the V and J regions
- No dedicated D segments
- Multiple germline V and J gene segments present
- V-J recombination during development joins one V and J segment
- Constant (C) region is encoded by a single C exon (Cκ or Cλ)
- No class switching occurs for light chains
In terms of similarities:
- Both use V(D)J recombination to assemble the variable domain exons
- Somatic hypermutation occurs in the rearranged V regions of both
Key differences:
- Heavy chains have dedicated D segments, light chains do not
- Heavy chains undergo class switching, light chains have single C isotype
- Heavy chain locus is much larger due to multiple C region isotype genes
So in summary, while both use genomic rearrangement of V, (D), J gene segments to construct the variable domain, the immunoglobulin heavy chain locus is more complex, allowing class switching between different heavy chain isotypes. Light chains lack dedicated D segments and isotype switching capability.
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Source: Claude 3 Sonnet response prompted and edited by Joel Graff.
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