T cell receptor genes are very similar to immunoglobulin genes in their organisation. The TCR beta locus contains V, D and J segments like the IgH locus and the TCR alpha locus contains V and J segments like the Ig light chain loci. In fact the mechanism of gene rearrangement for T cell receptors is essentially identical to Ig gene rearrangement. Mutations which lead to a failure of rearrangement affect both Ig and TCR; such mutations produce a lack of both T and B cells and therefore a complete lack of adaptive immunity and a severe immunodeficiency (SCID) which is naturally fatal.
The combinatorial diversity of T cell receptors is similar to that in immunoglobulin, though somewhat differently arrived at.
There are two major differences between TCR and Ig receptor diversity
- T cell receptors make more use of N-region
diversity for introduction of new amino acids in the CDR3 region.
This makes sense since the CDR3 region is believed to interact with
antigenic peptide in the MHC cleft.
The CDR3 region is significantly more diverse than CDR1,CDR2.
- T cell receptors do not undergo somatic hypermutation. There is no mechanism for selection of any somatic mutations which might naturally occur in TCR genes and no affinity maturation in the sense in which this occurs in Ig.
Information provided by: http://www-immuno.path.cam.ac.uk