Fig. 1

An overview of repertoire sequencing data production. The B-cell immunoglobulin receptor (BCR) is composed of two identical heavy chains (generated by recombination of V, D and J segments), and two identical light chains (generated by recombination of V and J segments). The large number of possible V(D)J segments, combined with additional (junctional) diversity introduced by stochastic nucleotide additions/deletions at the segment junctions (particularly in the heavy chain), lead to a theoretical diversity of >10¹⁴. Further diversity is introduced into the BCR during adaptive immune responses, when activated B cells undergo a process of somatic hypermutation (SHM). SHM introduces point mutations into the DNA coding for the BCR at a rate of ~10⁻³ per base pair per division [119, 120]. B cells accumulating mutations that improve their ability to bind pathogens are preferentially expanded in a process known as affinity maturation. The biology underlying these processes has been reviewed previously [121]. BCR repertoire sequencing (Rep-seq) experiments can be carried out on mRNA (shown here) or genomic DNA. Sequencer image: A MiSeq from Illumina/Konrad Förstner/Wikimedia Commons/Public Domain. 5′ RACE 5′ rapid amplification of cDNA ends, UMI unique molecular identifier, 5′ UTR 5′ untranslated region