Paeoniflorin ameliorates murine lupus nephritis by increasing CD4Foxp3 Treg cells via enhancing mTNFα-TNFR2 pathway.

Treg cells are essential for re-establishing self-tolerance in lupus. However, given that direct Treg therapies may be inadequate to control autoimmunity and inflammation, a strategy of inducing or expanding endogenous Treg cells in vivo may be a good option. Macrophages are main tissue-infiltrating cells and play a role in promoting Treg differentiation while paeoniflorin (PF), a monoterpene glycoside, exhibits anti-inflammatory and immunoregulatory effects. Here, we studied the effects of PF on CD4FoxP3 Treg frequency and the potential mechanisms involving M2 macrophages. We demonstrated that PF ameliorated lupus nephritis in lupus-prone B6/gld mice by reducing urinary protein, serum creatinine and anti-dsDNA levels, diminishing renal cellular infiltration, improving renal immunopathology and downregulating renal gene and protein expressions of key cytokines, including IFN-γ, IL-6, IL-12 and IL-23. PF also lowered the percentage of CD44CD62L effector T cells while augmenting CD4FoxP3 Treg frequency in B6/gld mice. Importantly, PF increased TNFR2 expression on CD4FoxP3 Tregs, but not CD4FoxP3 T cells, in vivo and in vitro. Furthermore, we found that CD206 subset of F4/80CD11b macrophages expressed a higher level of mTNF-α than their CD206 counterparts while PF increased mTNF-α expression on CD206 macrophages in vitro and in vivo. In vitro studies showed that mTNF-α M2 macrophages were more potent in inducing Treg differentiation and proliferation than their mTNF-α counterparts, whereas the effects of mTNF-α M2 macrophages were largely reversed by separation of M2 macrophages using a transwell or TNFR2-blocking Ab in the culture. Finally, PF also promoted in vitro Treg generation induced by M2 macrophages. Thus, we demonstrated that mTNFα-TNFR2 interaction is a new mechanism responsible for Treg differentiation mediated by M2 macrophages. We provided the first evidence that PF may be used to treat lupus nephritis.