B-CELLS SPECIFIC FOR BROMELAIN-TREATED ERYTHROCYTES ORE NOT DERIVED FROM ADULT-RAT BONE-MARROW

As part of an evolutionary layered hematopoietic system, the B lymphoc yte compartment consists of different lineages of B lymphocytes, which evolve sequentially during ontogeny. In mice, there is ample evidence for the existence of at least two lineages, a layer of B-1 cells (Ly- 1 B cells) and the evolutionary more advanced layer consisting of conv entional B cells. In a previous study we were unable to detect B-1 cel ls in the rat as determined by phenotypic markers. Here we studied the possible existence of putative B-1 cells in the rat based on some fun ctional and developmental characteristics as have been described for m ouse B-1 cells. We show that B cells secreting antibodies that recogni ze bromelain-treated mouse red blood cells (BrMRBC) can be identified in rat spleen, whereas these cells (in contrast to DNP-specific B cell s) are virtually absent in lethally X-irradiated and bone marrow (BM) reconstituted animals. The number of anti-rMRBC-secreting B cells coul d not be restored to control levels by reconstitution with fetal liver cells or by cotransfer of 107 cells from peritoneal cavity, lymph nod e or Peyer's patches or up to 2x10(8) splenocytes. Although our findin gs thus suggest that B-1 cells (or B-1 like cells) may be present in r ats, formal proof for the existence of such a lineage in rats awaits d efinition of these cells at the progenitor level.