Ontogeny, distribution and function of CD38-expressing B lymphocytes in mice.

Analysis of expression of CD38, CD45R (B220), IgM and IgD on splenic B lymphocytes from mice of different ages demonstrated CD38 on both immature (B220(+), BCR(-)) and mature (B220(+), BCR(+)) B lymphocytes. Similarly, CD38 is expressed as early as B220 on the surface of progenitor B cells in the bone marrow. In spite of expressing of CD38 and IgM, neonatal B cells, in contrast to the adult, failed to proliferate to either anti-CD38 or anti-IgM cross-linking when IL-4 was present. They did, however, respond to LPS and anti-CD40, and by 2 weeks of age they began to respond to anti-CD38 and anti-IgM, reaching adult B cell levels by 4 weeks. Although the distribution of CD38 on adult B cells from most different lymphoid compartments was broadly similar, significantly higher levels of CD38 were expressed on peritoneal B lymphocytes. A detailed analysis, using IgM / IgD ratio and staining with anti-CD5 confirmed that B1 lymphocytes were expressing a high level of CD38. Interestingly, both immature B cells and peritoneal B1 lymphocytes were unresponsive to anti-CD38. However, they were activated by LPS or anti-CD40.