The TCR[beta] chain consists of variable (V), joining (J), diversity (D) and constant (C) regions encoded by gene segments spanning 685 kilobases of human chromosome seven. Diversity and antigen specificity of T-cell antigen recognition is primarily attributed to the hypervariable, or third complementarity-determining region (CDR3), or the TCR[beta] chain, and is achieved by non-templated nucleotide additions or deletions during TCR gene rearrangements. Antigen driven T cell responses are observable as perturbations in the Gaussian-like distributions of CDR3 gene fragment lenghts of TCR families, because responding antigen-specific cells are retained in the memory lymphocyte pool, permanently altering the distributions of cells within the T cell repertoire. Therefore, analysis of CDR3 lenghts provides an assessment of the frequency and diversity of the T cell response to antigenic exposure.

Both central and effector memory subsets express disturbed repertories. Some BV families are overexpressed, especially in the effector CD62L- subset.