PD‐L2 expression extends beyond dendritic cells/macrophages to B1 cells enriched for V_H11/V_H12 and phosphatidylcholine binding

Abstract

B1 B cells are the major source of natural antibody that is essential for innate immunity. The B1 repertoire is skewed toward production of phosphatidylcholine (PtC)-binding V H 11 and V H 12 immunoglobulin that plays a key role in immune defense against bacterial infection. Programmed death-ligand 2 (PD-L2) is a ligand for the immunosuppressive receptor programmed death-1 (PD-1). It has been reported that expression of PD-L2 is restricted to dendritic cells and macrophages in mice. Here we show that 50-70% of resting peritoneal B1 cells express PD-L2, which is not present or inducible on conventional B2 B cells or PD-L2 -B1 cells. Although PD-L2 + and PD-L2 -B1 cells are similar in proliferative responses and spontaneous immunoglobulin secretion, PD-L2 + B1 cells are highly enriched for expression of V H 11 and V H 12 genes and encompass the bulk of PtC-binding B1 cells. These findings extend the range of known PD-L2 expression to B cells and show that B1 cells identified by this marker express a specific repertoire associated with anti-bacterial immunity. IntroductionB1 B cells comprise a unique subset of B cells distinguished phenotypically, ontogenetically, and functionally from conventional (B2) B cells [1][2][3]. B1 B cells are the major source of natural immunoglobulin in normal unimmunized mice, providing a vital front line defense against bacterial and viral infection [4][5][6][7][8]. This function is associated with a skewed repertoire containing autoreactive specificities, one manifestation of which is expression of phosphatidylcholine (PtC)-binding V H 11 and V H 12 by a substantial portion of peritoneal B1 cells in unimmunized mice [9][10][11]. PtC is the polar headgroup of common membrane phospholipids. Reconstitution of anti-PtC IgM in sIgM-deficient mice substantially reduced the bacterial load in a cecal ligation and puncture model [5]. Thus, V H 11/V H 12-expressing B1 cells play an important role in immunity; considering that PtC-binding B1 cells recognize protease-treated autologous erythrocytes, they may play a role in hemolytic autoimmune dyscrasias as well [10,12].B cells, like T cells, express programmed death-1 (PD-1), engagement of which negatively regulates B cell activity in vitro [13]. Surface levels of PD-1 are upregulated by BCR stimulation and down-regulated by Results and discussionPeritoneal B1 cells uniquely express PD-L2To evaluate PD-L1 and PD-L2 expression, cells from normal peritoneal washout fluids and spleens were stained with fluorescent antibodies to identify B1 cells, B2 cells and T cells and were counterstained to detect PD-L1 and PD-L2. Like B2 cells and T cells, B1 cells expressed a basal level of PD-L1, although to a much greater extent (Fig. 1A). Surprisingly, we found that a significant portion of peritoneal B1 cells (50-70%) expressed PD-L2, whereas B2 cells and T cells failed to do so (Fig. 1A). A smaller and less distinct population of splenic B1 cells also expressed PD-L2. To exclude the possibility of staining artifacts, we sorted PD-L2 + and PD-L2 -periton...

BLyS inhibition eliminates primary B cells but leaves natural and acquired humoral immunity intact

“…2 A and B), reducing both B1a and B1b subsets in the spleen. To assess B1 function, we measured the number of spontaneous IgM anti-PC antibody-producing cells, because B1 cells are the main producers of such antibodies (15). The numbers of these cells were similar in both spleen and PerC in mice treated with anti-BLyS or isotype control antibody, although variance in the spleen was higher in controls (Fig.…”

Costimulatory Pathways in Multiple Sclerosis: Distinctive Expression of PD-1 and PD-L1 in Patients with Different Patterns of Disease

“…Although these data were subsequently partially refuted by other results showing that PD-L2 can play a role in EAE in some mice strains (16), we felt supported in our decision by the observation that the expression of PD-L2 is much more restricted than that of PD-L1. Thus, whereas PD-L1 is constitutively expressed on a wide range of hematopoietic and nonhematopoietic cells (46,51,52), PD-L2 is only inducible expressed in dendritic cells, macrophages, and mast-cells (46,(51)(52)(53). Incubation of PBMC of AMS patients with PD-1-specific neutralizing Abs resulted in the increased proliferation of MBP-specific CD4 ϩ and CD8 ϩ T lymphocytes.…”

Programmed Death (PD)-1:PD-Ligand 1/PD-Ligand 2 Pathway Inhibits T Cell Effector Functions during Human Tuberculosis

“…It is widely known that the two PD-1 ligands differ in their expression patterns: PD-L1 is expressed on T cells, B cells, dendritic cells, macrophages, nonhematopoietic and other cell types, while expression of PD-L2 is much more restricted to dendritic cells, B1 cells, and macrophages (16,26). Here, we found that both PD-1 ligands were inducibly expressed on T cells from tuberculosis patients in response to M. tuberculosis, demonstrating for the first time that PD-L2 is expressed on human T cells.…”