PD-L2 expression extends beyond dendritic cells/macrophages to B1 cells enriched for V(H)11/V(H)12 and phosphatidylcholine binding.

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.