Adult BM generates CD5⁺ B1 cells containing abundant N‐region additions

Abstract

The self-renewing capacity of B1 cells infers homeostatic regulation; however, previous work suggests the low level of N-region addition characterizing B1 cells early in life increases with age, which implies that the B1-cell population is not a closed system. To explore this, we evaluated Nregion addition in CD5 + B1 cells generated from adult BM. Adult BM cells were marked with GFP introduced by mouse stem cell virus transduction, and were then adoptively transferred into lethally irradiated recipients. Within 2-3 months, we found GFP-marked CD5 + B cells in the peritoneal cavities of recipients, which we demonstrate here meet a variety of criteria for B1-cell traits including Mac-1 surface expression; annexin, elfin, and Pax-5 gene expression; mitogenic responsiveness to phorbol ester; and spontaneous immunoglobulin secretion. Notably, we found by single-cell PCR that this population of BM-derived CD5 + B1 cells expressed immunoglobulin with abundant Nregion addition (and little V H 11/V H 12 skewing), unlike CD5 + B1 cells obtained from unmanipulated animals but reminiscent of B2 cells. Further, we confirmed that native CD5 + B1 cells from older mice contain more N-region additions than native CD5 + B1 cells from younger mice. These results suggest that adult BM progenitors contribute to the peritoneal CD5 + B1-cell pool over time.

Siglec-G Regulates B1 Cell Survival and Selection

“…They use the long J H 1 element (19 potential CDR3 nucleotides) more frequently and the short J H 2 and J H 3 (14 nucleotides) less frequently than do B2 cells (33). In terms of N nucleotide insertion and V H 11/V H 12 usage, B1a cells derived from adult bone marrow resemble B2 cells rather than normal B1a cells (34,35 + , B220lo), longevity in vitro, and production of natural Abs. However, they differ in respect to other features like the BCR repertoire.…”

Ordering human CD34+CD10−CD19+pre/pro-B-cell and CD19−common lymphoid progenitor stages in two pro-B-cell development pathways

“…In adult BM, human pre/pro-B-cell frequencies are well below those detected in CB (21,35), and mouse B-1 cells belong to the B-1b lineage that bears TdT activity and are, by that criterion, like the B-2 lineage (8,36). The mouse B-1a-and B-2-lineage biology is markedly different (7-9) and may resemble aspects of the human pre/pro-B and CLP/early-B-cell pathways, at least in CB and S17 in vitro systems analyzed, respectively.…”

“…Recent reports nonetheless show that the B-cell development process is much more plastic than originally thought and generates multiple B lineages with distinct biological features that are medically relevant (9,(37)(38)(39). Mouse B1a cells have unilineage precursors that acquire CD19 before the conventional CLP marker appears days before B2-lineage onset in the fetus and show the absence of TdT-mediated N-nucleotide addition at their HCDR3 (7,8,36). This HCDR3 repertoire is essential for generating perinatal antibodies with nonrandom "germline-encoded" specificities ("canonical" Igs); in mice, these antibodies are needed for acquisition of complete protective immune defense from lethal bacterial pathogens and production of natural autoantibodies (37,28).…”

B-1a transitional cells are phenotypically distinct and are lacking in mice deficient in IκBNS

“…We next investigated whether the lack of B-1 cells in bumble was due to B cell-autonomous defects or alterations in the stromal microenvironment. As noted previously, initial studies showed that B-1 cells were generated from adult wt bone marrow when transferred into immunodeficient hosts (24)(25)(26)(27). To distinguish between extrinsic and intrinsic contributions to the bumble phenotype, we mixed bone marrow from bumble (CD45.2) and wt (CD45.1) mice and transferred it into irradiated RAG1…”