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CDR3 length in antigen-specific immune receptors
E P Rock1, P R Sibbald, M M Davis
1Department of Microbiology and Immunology, Stanford University, California 94305.
The Journal of Experimental Medicine
|January 1, 1994
Summary
The complementarity determining region 3 (CDR3) loop sequences in immunoglobulins (Ig) and T cell receptors (TCR) exhibit significant size variation. Gamma/delta TCRs share CDR3 size similarities with Igs, suggesting distinct recognition properties compared to alpha/beta T cells.
Area of Science:
- Immunology
- Molecular Biology
- Structural Biology
Background:
- Lymphocyte receptors, including immunoglobulins (Ig) and T cell receptors (TCR), generate vast diversity through V(D)J recombination.
- The complementarity determining region 3 (CDR3) loop is a key site of this diversity, crucial for antigen binding in Igs and peptide recognition in TCRs.
- Understanding the physical and selective constraints on CDR3 sequences is vital for deciphering immune recognition mechanisms.
Purpose of the Study:
- To compile and analyze CDR3 size variation across different Ig and TCR chains (Ig H, L; TCR alpha, beta, gamma, delta).
- To investigate the physical and selective constraints shaping CDR3 length distributions.
- To infer potential differences in ligand binding properties between distinct T cell populations based on CDR3 characteristics.
Main Methods:
- Compilation of existing data on CDR3 loop lengths for Ig heavy (H), Ig light (L, kappa and lambda), and TCR alpha, beta, gamma, and delta chains.
- Statistical analysis of CDR3 size distributions and variability across different receptor types.
- Comparative analysis of CDR3 length profiles to infer functional similarities and differences.
Main Results:
- Significant variability in CDR3 size was observed, with Ig heavy and TCR delta chains showing the greatest length heterogeneity.
- Ig H and TCR delta CDR3s are notably longer than their respective Ig L and TCR gamma counterparts.
- TCR alpha and beta chain CDR3 length distributions are highly constrained and unaffected by thymic selection, displaying nearly identical average lengths.
Conclusions:
- CDR3 length profiles suggest a closer functional resemblance between gamma/delta TCRs and Igs in their ligand-binding regions compared to alpha/beta TCRs.
- The distinct CDR3 size constraints imply fundamentally different recognition properties and ligand specificities between gamma/delta and alpha/beta T cells.
- These findings contribute to a deeper understanding of the structural basis for T cell receptor diversity and function.