Acute rejection (AR), initiated by alloreactive CD4 + T cells, hampers allograft survival. Soluble fibrinogen-like protein 2 (sFGL2) is a novel effector of CD4 + T cells. We previously found that serum sFGL2 significantly increased in renal allograft recipients with AR. In this study, sFGL2 secretion by CD4 + T cells and its mechanism were further explored both in vivo and in vitro.Forty cases of living-related renal transplant recipients with biopsy-proven AR or stable renal function were collected and detected serum sFGL2, tumor necrosis factor (TNF)-α and interferon (IFN)-γ, and peripheral CD4 + T cells. In vitro, the isolated human CD4 + T cells were stimulated by TNF-α or IFN-γ. sFGL2 in the supernatant and mitogen-activated protein kinase (MAPK) proteins in the CD4 + T cells were investigated. Approval for this study was obtained from the Ethics Committee of Fudan University.sFGL2, TNF-α, IFN-γ, and CD4 + T cells were significantly increased in the peripheral blood of renal allograft recipients with AR. Stimulation with 1000 U/mL TNF-α or 62.5 U/mL IFN-γ for 48 h provided an optimal condition for CD4 + T cells to secrete sFGL2 in vitro. Phosphorylated (p-) c-Jun N-terminal kinase was remarkably upregulated in the activated CD4 + T cells, whereas no significant changes were found in p-p38 MAPK or p-ERK1/2 expression. Furthermore, inhibition of c-Jun N-terminal kinase significantly reduced sFGL2 secretion by CD4 + T cells.sFGL2 secretion by CD4 + T cells can be induced with TNF-α and IFN-γ stimulation through MAPK signaling in renal allograft AR. Our study suggests that sFGL2 is a potential mediator in the pathogenesis of allograft rejection.