A VH11Vκ9 B Cell Antigen Receptor Drives Generation of CD5+ B Cells Both In Vivo and In Vitro

Abstract

B lymphocytes can be divided into different subpopulations, some with distinctive activation requirements and probably mediating specialized functions, based on surface phenotype and/or anatomical location, but the origins of most of these populations remain poorly understood. B cells constrained by transgenesis to produce an Ag receptor derived from a conventional (B-2) type cell develop a B-2 phenotype, whereas cells from mice carrying a B-1-derived receptor acquire the B-1 phenotype. In this study transgenic enforced expression of a B cell receptor (μ/κ) originally isolated from a CD5+ (B-1a) B cell generates B-1 phenotype cells in bone marrow cultures that show a distinctive B-1 function, survival in culture. Despite their autoreactivity, we find no evidence for receptor editing or that the paucity of B-2 cells is the result of tolerance-induced selection. Finally, Ca2+ mobilization studies reveal a difference between transgenic B-1 cells in spleen and peritoneal cavity, with cells in spleen much more responsive to anti-B cell receptor cross-linking. We discuss these results in terms of specificity vs lineage models for generation of distinctive B cell subpopulations.

The Unique Antigen Receptor Signaling Phenotype of B-1 Cells Is Influenced by Locale but Induced by Antigen

“…Yet the expression levels of other cell surface markers used to differentiate B-1 from B-2 cells, including the presence of CD5 and CD43 and absence of CD23, were similar on splenic and peritoneal V H 11V 9 B cells, suggesting a B-1 classification. And, despite the higher B220 and lower IgM expression levels in the splenic cells, they do not match the levels of B220 and IgM expressed on normal splenic B-2 cells from NTg or 3-83 ␦ Ig transgenic control mice (22).…”

“…Splenic and peritoneal B cells were prepared as previously described (22). Briefly, purified splenic B cells were obtained by Percoll gradient separation after RBC and T cell lysis; peritoneal B cells were purified from peritoneal lavage by removal of adherent accessory cells and magnetic bead depletion of T cells.…”

“…We have previously determined that splenic V H 11V 9 B cells not only survive long-term in vitro (22), but can also survive long-term in the peritoneum when transferred i.p. into NTg recipient mice (Fig.…”

“…This rearrangement is expressed by 5-15% of the peritoneal B-1 cells in normal mice and reacts with phosphatidylcholine (PtC), a normal component of the cell membrane (24). We recently reported that B cells constrained by a V H 11V 9 Ig transgene generated CD5 ϩ , PtC-specific B cells in both the spleen and peritoneum (22). Interestingly, splenic B cells from V H 11V 9 mice exhibit low basal intracellular free Ca 2ϩ ([Ca 2ϩ ] i ) levels, and mobilize Ca 2ϩ following BCR aggregation, suggesting that they are functionally equivalent to nonautoreactive, conventional B-2 cells.…”

Transgenic Expression of a Human Polyreactive Ig Expressed in Chronic Lymphocytic Leukemia Generates Memory-Type B Cells That Respond to Nonspecific Immune Activation

“…Engagement of the BCR is believed to influence the differentiation of a B cell into a particular B cell subset, as well as the peripheral lymphoid compartment in which it resides, and is best demonstrated for the B-1 (18,54) and MZ (17, 48) B cell lineages. SMI mice have significantly higher percentages of human Ig-expressing peritoneal B cells that express CD5 than do AB29 mice.…”