Dr. Yuval Elhanati, École Normale Supérieure, Paris
Wednesday, February 19th, at 12:30 in room 430 Fishbach
19 February, 2014
Identifying selection pressures in somatic immune receptor evolution
Immune receptor diversity is an essential component of the immune system, allowing the organism to effectively respond to a wide variety of threats. The diversity of T-cell receptor repertoire sequences is the end result of two different processes – the generation of the initial repertoire in the thymus by DNA recombination and the functional selection of T cells by interactions with self and foreign peptides. Analyzing high throughput data on CDR3-region sequences of human CD4+ T-cell receptor beta chains we use maximum likelihood methods to disentangles selection on amino acids from biases in the generated repertoire. We find a correlation between generation and selection, which suggests that natural evolution of the recombination process anticipates somatic evolution. Comparing the pre-selected repertoire with the post-selected naïve and memory cells ones we show that thymic selection significantly reduces the diversity of the repertoire. We also find that the naïve and memory repertoires are statistically similar.