Bee Venom Phospholipase A2 Induces Regulatory T Cell Populations by Suppressing Apoptotic Signaling Pathway

Bee venom phospholipase A2 is a lipolytic enzyme in bee venom that catalyzes hydrolysis of the sn-2 ester bond of membrane phospholipids to produce free fatty acid and lysophospholipids. Current evidence suggests that bee venom phospholipase A2 (bvPLA2) induces regulatory T cell expansion and attenuates several immune system-related diseases, including Alzheimer's disease. The induction of Treg cells is directly mediated by binding to mannose receptors on dendritic cells. This interaction induces the PGE2-EP2 signaling pathway, which promotes Treg induction in CD4(+) T cells. In this study, we investigated the effects of bvPLA2 treatment on the apoptotic signaling pathway in Treg populations. Flow cytometry was performed to identify early apoptotic cells. As a result, early apoptotic cells were dramatically decreased in bvPLA2-treated splenocytes, whereas rapamycin-treated cells showed levels of apoptotic cells similar to those of PBS-treated cells. Furthermore, bvPLA2 treatment increased expression of anti-apoptotic molecules including CTLA-4 and PD-1. The survival rate increased in bvPLA2-treated Tregs. Our findings indicate that bvPLA2-mediated modulation of apoptotic signaling is strongly associated with the Treg induction, which exhibits protective effects against various immune-related diseases. To our knowledge, this study is the first to demonstrate that bvPLA2 is the major bee venom (BV) compound capable of inducing Treg expansion through altering apoptotic signal.