Two weeks of daily peritoneopheresis of adult mice result in the selec
tive depletion of B-1 cells, followed by the appearance of a populatio
n of B220(+)IgM(-) lymphocytes in the peritoneal cavity. These cells s
hare with bone marrow (BM) pre-B cells expression of lambda 5, V-preB,
and RAG-1 genes and a higher fraction of unrearranged V to DJ heavy (
H) chain immunoglobulin (Ig) gene segments,when compared with mature B
lymphocytes. Upon transfer to SCID recipients, sorted peritoneal B220
(+)IgM(-) cells fail to colonize the BM, repopulate very few B cells i
n the spleen, but entirely reconstitute the B-1 cell compartment in th
e peritoneal and pleuropericardial cavities, In contrast, parallel tra
nsfers of sorted BM B220(+)IgM(-) cells result in reconstitution of th
e BM and spleen B lineage cell compartments, but in no coelomic B cell
repopulation. Both types of pre-B cells reconstitute splenic plasma c
ells of donor origin, but with markedly distinct efficiencies: the rat
io of IgM-plasma cell/B cell numbers in the spleens of peritoneal pre-
B cell recipients is more than 500-fold higher than that of recipients
reconstituted by BM pre-B cells. We take these data to indicate that
(1) differentiative commitment to the B-1 cell population occurs befor
e selection events on mature cells; (2) B-1 precursors exist or may be
locally produced in the adult mouse; (3) there is a lineage-related d
ifferential ability of mature B cells to undergo terminal differentiat
ion to high-rate Ig secretion.