PHENOTYPE OF B-CELLS RESPONDING TO THE THYMUS-INDEPENDENT TYPE-2 ANTIGEN POLYVINYL PYRROLIDINONE

We have determined the origin and cell surface phenotype of B cells pr oducing antibody in response to immunization with the non-self TI-2 an tigen polyvinyl pyrrolidinone (PVP), We report that the responding cel ls are derived from precursors in adult bone marrow and display the ph enotype characteristic of B-1 cells, By use of allotype marked chimeri c mice, constructed by reconstituting lethally irradiated recipients w ith adult bone marrow and peritoneal B-1 lymphocytes of recognizably d ifferent Ig allotypes, immunized with 1 mu g PVP, we found that althou gh a substantial part of the total IgM produced in these chimeras bore the allotype of the transferred peritoneal B-1 cells, essentially all of the anti-PVP IgM expressed the allotype of the adult bone marrow. Fifteen of 16 hybridomas derived from a normal PVP-immune adult mouse bore N nucleotides at the V-D and DJ junctions of their heavy chain CD R3 regions, indicating their origin from precursors in the adult bone marrow, By use of ELISA spot analysis, we found the cells responding t o PVP to be localized in the spleens of normal immunized mice, We then used multiparameter flow cytometric sorting to determine the cell sur face phenotype of these cells. We found that the cells producing anti- PVP were greatly enriched in a small subpopulation with the phenotypic characteristics of B-1 cells; they were B220(intermediate), CD5(low), IgM(high), IgD(low), CD43(+) and CD23(-). This subpopulation was also enriched for all cells producing IgM, regardless of specificity (the so-called 'spontaneous' antibody), We conclude that the B-1 phenotype is more likely a marker for a state of differentiation than for a disc rete lineage of B cells.