CD5+/Mac-1- peritoneal B cells: a novel B cell subset that exhibits characteristics of B-1 cells.
The peritoneal cavity of mice is enriched for B-1 B cells, a lymphocyte subset that differs from conventional B-2 cells phenotypically, functionally, and developmentally. According to current paradigms, all peritoneal B-1 cells express Mac-1 whereas B-2 cells do not and thus these populations are often purified by FACS sorting or magnetic bead isolation based on B cell expression of Mac-1 or lack thereof. However, in the course of studying B220+/Mac-1- peritoneal B-2 cells, we discovered that this population is actually heterogeneous, with approximately 30-40% of these B220+/Mac-1- cells expressing the B-1 cell marker CD5. It was unclear whether this B220+/CD5+/Mac-1- peritoneal B cell population represented aberrantly CD5 expressing B-2 cells or Mac-1- B-1 cells. To address this issue we tested CD5+/Mac-1- peritoneal B cells for several traits that distinguish B-1 and B-2 cells. We found that CD5+/Mac-1- peritoneal B cells resembled CD5+ B-1 cells and not B-2 cells in terms of expression of several additional surface markers (IgM, IgD, CD23, CD43, and CD80). Further, CD5+/Mac-1- peritoneal B cells expressed high levels of V(H)11 and V(H)12, two Ig variable genes that are expressed mainly by B-1 but not B-2 cells. In addition, CD5+/Mac-1- peritoneal B cells responded to PMA, a mitogen that stimulates B-1 cells but not B-2 cells, and not to anti-Ig, that stimulates B-2 cells but not B-1 cells. ELISPOT analyses of freshly isolated CD5+/Mac-1- peritoneal B cells revealed that they secreted IgM constitutively, like B-1 cells and unlike B-2 cells. These results indicate that CD5+/Mac-1- peritoneal B cells are a new subset of B-1 cells, here termed B-1c, and stress the importance of using multiple surface markers to identify and purify specific B cell populations.
Department of Microbiology, Boston University School of Medicine, Boston, MA 02118, USA.
William D
WD
Hastings
Sean M
SM
Gurdak
Joseph R
JR
Tumang
Thomas L
TL
Rothstein
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D018956:CD5 Antigens / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D005803:Genes, Immunoglobulin; D007075:Immunoglobulin M / Q000096:biosynthesis; D016177:Macrophage-1 Antigen / Q000378:metabolism; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D010529:Peritoneal Cavity / Q000166:cytology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D018956:CD5 Antigens; D018076:DNA, Complementary; D007075:Immunoglobulin M; D016177:Macrophage-1 Antigen; D012333:RNA, Messenger; C033027:secretory IgM