B-1 cells in the bone marrow are a significant source of natural IgM

Youn Soo Choi, Jacquelyn A. Dieter, Kristina Rothaeusler, Zheng Luo, Nicole Baumgarth

Research output: Contribution to journalArticlepeer-review

115 Scopus citations


Natural IgM antibodies secreted in the absence of antigenic challenge are important contributors to antimicrobial immunity and tissue homeostasis. Early studies identified BM and, to a lesser extent the spleen, as main tissue sources of this spontaneously secreted IgM. However, the responsible B-cell subset has never been identified. Using multicolor flow cytometry, cell sorting and chimeric mice in which B-1 and B-2 cells and their secreted antibodies are distinguished by their Ig-allotype, we unequivocally identify the natural IgM-secreting cells in spleen and, for the first time, in the BM as IgM + IgD lo/-CD19 hi CD43 + CD5 +/- B-1 cells. The newly identified population of BM B-1 cells shows many of the phenotypic characteristics of splenic B-1 cells but is distinct from B-1 cells in the peritoneal cavity, which generate at best very small amounts of IgM. Antibody-secreting spleen and BM B-1 cells are distinct also from terminally differentiated plasma cells generated from antigen-induced conventional B cells, as they express high levels of surface IgM and CD19 and lack expression of CD138. Overall, these data identify populations of non-terminally differentiated B-1 cells in spleen and BM as the most significant producers of natural IgM.

Original languageEnglish (US)
Pages (from-to)120-129
Number of pages10
JournalEuropean Journal of Immunology
Issue number1
StatePublished - Jan 2012


  • Animal model
  • Antibodies
  • B cells
  • BM
  • Immunoglobulins

ASJC Scopus subject areas

  • Immunology
  • Immunology and Allergy


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