Supplementary Material for: Postnatal and Adult Immunoglobulin Repertoires of Innate-Like CD19<sup>+</sup>CD45R<sup>lo</sup> B Cells

The diversity in antibody repertoire relies on different B cell populations working efficiently to fulfil distinct specific functions. We recently described an innate-like CD19<sup>+</sup>CD45R<sup>-/lo</sup> (19<sup>+</sup>45R<sup>lo</sup>) cell population in postnatal unstimulated adult mice, a heterogeneous population containing cells expressing immunoglobulin M (IgM) and others behaving as differentiated mature B lymphocytes (intracytoplasmic IgG1, AID<sup>+</sup>, Blimp-1<sup>+</sup>RAG2<sup>-</sup>). In the present study, we characterized the Ig repertoire expressed by splenic 19<sup>+</sup>45R<sup>lo</sup> cells, assuming that they would bear a restricted repertoire biased for germline rearrangements and low mutation rates similar to other innate-like cells. Sequences from 19<sup>+</sup>45R<sup>lo</sup> cells displayed a variety of V, D and J regions, and the analysis of the CDR-H3 region revealed an intermediate overall CDR-H3 length and moderate hydrophobicity. Both IgM and switched sequences of PD15 19<sup>+</sup>45R<sup>lo</sup> cells had shorter CDR-H3 region and fewer non-template N nucleotides than adult sequences, as expected for profiles that correspond to an immature phenotype. Regarding the mutation rate in the VH regions, IgG1 sequences already carried a high rate of replacement mutations at PD15, which increased further in the sequences obtained from adult mice. Moreover, statistical models suggest that a proportion of the switched sequences in adult 19<sup>+</sup>45R<sup>lo</sup> cells had experienced antigen selection, unlike other innate-like B cell compartments.