Origins and functions of B-1 cells with notes on the role of CD5.
Whether B-1a (CD5+) cells are a distinct lineage derived from committed fetal/neonatal precursors or arise from follicular B-2 cells in response to BCR ligation and other, unknown signals remains controversial. Recent evidence indicates that B-1a cells can derive from adult precursors expressing an appropriate specificity when the (self-) antigen is present. Antibody specificity determines whether a B cell expressing immunoglobulin transgenes has a B-2, B-1a or marginal zone (MZ) phenotype. MZ cells share many phenotypic characteristics of B-1 cells and, like them, appear to develop in response to T independent type 2 antigens. Because fetal-derived B cell progenitors fail to express terminal deoxynucleotidyl transferase (TdT) and for other reasons, they are likely to express a repertoire that allows selection into the B-1a population. As it is selected by self-antigen, the B-1 repertoire tends to be autoreactive. This potentially dangerous repertoire is also useful, as B-1 cells are essential for resistance to several pathogens and they play an important role in mucosal immunity. The CD5 molecule can function as a negative regulator of BCR signaling that may help prevent inappropriate activation of autoreactive B-1a cells.
Berland
Robert
R
Department of Pathology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA. rberland@opal.tufts.edu
Wortis
Henry H
HH
D000818:Animals; D015551:Autoimmunity; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology*; D001854:Bone Marrow Cells / Q000166:cytology / Q000276:immunology; D018956:CD5 Antigens / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D005333:Fetus / Q000166:cytology / Q000276:immunology; D006801:Humans; D018928:Immunity, Mucosal; D007070:Immunoglobulin A / Q000096:biosynthesis; D007075:Immunoglobulin M / Q000097:blood; D008213:Lymphocyte Activation; D051379:Mice; D010641:Phenotype; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D015398:Signal Transduction
D018956:CD5 Antigens; D007070:Immunoglobulin A; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell