B10 Promotes Polarization and Pro-Resolving Functions of Bone Marrow Derived Macrophages (BMDM) Through PD-1 Activation

Regulatory B cells (B regs) are immune cells that help suppress excessive inflammatory responses by interacting with other immune components. Among them, B-10 cells are known for their strong immunoregulatory function. This study focused on how B-10 cells influence macrophage phenotype and function through the PD-1 signaling pathway. To investigate this, B-10 cells derived from mouse spleens were co-cultured with bone marrow-derived macrophages (BMDMs) from either wild-type (WT) or PD-1 knockout (PD-1 KO) mice, using both direct contact and Transwell setups. The findings indicated that direct co-culture with B-10 cells significantly promoted the polarization of macrophages towards the anti-inflammatory M2 type, characterized by increased expression of surface markers (F4/80⁺, CD206⁺, CD163⁺), higher levels of PD-1, and upregulation of M2-related genes (<i>IL-1ra</i>, <i>IL-10</i>, <i>Arg-1</i>, <i>IL-6</i>, and <i>CCL1</i>). These macrophages also exhibited enhanced phagocytic activity and greater secretion of specialized pro-resolving mediator (SPMs) like RvD2 and 15-epi LXA4. In contrast, these effects were reduced when B-10 cells were cultured indirectly or when PD-1 was absent. These findings suggest that B-10 cells promote anti-inflammatory macrophage activity primarily through PD-1 signaling, offering insights into potential therapeutic approaches for controlling inflammation.