Peritoneal cavity B cells are precursors of splenic IgM natural antibodyproducing cells

peritoneal cavity B-1b cells with anti-Gal receptors produce anti-Gal IgM Abs only after LPS stimulation. Likewise, peritoneal cavity cells of GalT/ and wild-type mice do not produce IgM Abs of other specificities without LPS stimulation. Development of Ab-secreting capacity is associated with loss of CD11b/CD18 (Mac-1) expression. In contrast, there are large numbers of cells producing anti-Gal and other IgM Abs in fresh splenocyte preparations from GalT/ and (for non-Gal specificities) wild-type mice. These cells are Mac-1 but otherwise B-1b-like in their phenotype. We therefore hypothesized a pathway wherein peritoneal cavity B cells migrate into the spleen after activation in vivo and lose Mac-1 expression to become IgM Ab-producing cells. Consistent with this possibility, splenectomy reduced anti-Gal Ab production after immunization of GalT/ mice with Gal-positive rabbit RBC. Furthermore, splenectomized B6 GalT/, Ig -chain mutant (/) (both Gal- and B cell-deficient) mice produced less anti-Gal IgM than nonsplenectomized controls after adoptive transfer of peritoneal cavity cells from B6 GalT/ mice. When sorted GalT/ Mac-1 peritoneal cavity B cells were adoptively transferred to B6 GalT/, / mice, IgM Abs including anti-Gal appeared, and IgM-producing and Mac1 B cells were present in the spleen 5 wk after transfer. These findings demonstrate that peritoneal cavity Mac-1 B-1 cells are precursors of Mac-1 splenic IgM Ab-secreting cells. The Journal of Immunology, 2003, 171: 5406–5414. T he shortage of donor organs for transplantation has be-come a serious problem, paradoxically, because of thesuccess of transplantation. Xenotransplantation provides a potential solution of this organ shortage. The pig is considered t