When we try and reach the best coverage of the immunological repertoire, we actually aim to sequence as many immunoglobulin sequences as possible, out of the whole repertoire. That is, we aim to maximize the ratio between sequenced immunoglobulins (SI) to the total number of immunoglobulins (TI) in

the organism. We aim to reach an SI : TI ratio of 1. When this SI : TI ratio has been reached, an account for the entire repertoire can be obtained. Dorsomorphin solubility dmso Smaller model organisms, therefore, provide a better starting point from which to reach this ratio. Smaller organisms contain significantly fewer cells in total and, obviously, fewer immune cells. Much smaller organisms (e.g. the round worm) are sufficient for some aspects of immunology (see refs 31,32) but not for studying the lymphocyte repertoire. Zebrafish, Danio rario, are an ideal model system for studying the adaptive immune system for two reasons: first, they have the earliest recognizable adaptive immune system whose features match the essential human elements, and second, the zebrafish RG7420 immune system has only ∼ 300 000 antibody-producing B cells, making it three orders of magnitude simpler than mouse and five

orders of magnitude simpler than human. Recent works study the zebrafish B-cell repertoire via high throughput analysis.33 An important issue in the immune receptor diversity analysis is clone identification, e.g. classification of the obtained reads into clusters, under the assumption that relatively close sequences originate from the same clonally expanded cell. V(D)J segment identification is usually carried out by performing local alignment to germline sequences [available on the International ImMunoGeneTics (IMGT) database34]. However, D segment classification is more complex because of the short length of the sequence, as opposed to V and J genes. Furthermore, nucleotide deletions and P/N additions occur frequently during somatic recombination processes at the V–D and D–J junctions. Much immunological interest is focused on the complementarity determining region 3 (CDR3) of the chains,14,18–20,22,25,33 Farnesyltransferase the most

variable locus of the three CDR regions, and especially the β chain of the TCR.14,18–20,22,25 A recent study focused only on a small portion of the TCR-β repertoire by capturing only sequences generated by a specific gene recombination.22 Read length is a critical parameter in this case, as the entire V(D)J region is ∼ 300 nucleotides in length, including its V and J segments. This has been solved by either using the 454 method (with longer reads), the Douek approach (see above) or special methods of read assembly as in refs 14,25. Once sequences are available, different perspectives portray the repertoire: the size of the repertoire; similarities between repertoires; V(D)J segment use; nucleotide insertions and deletions; CDR lengths; and amino acid distributions along the CDRs.