Objective To investigate the effect and mechanism of the signal transducer and activator of transcription 3 (STAT3) inhibitor Stattic on the rejection of mouse heart allograft.

Methods BALB/c mice (donors) were used to transplant skin onto C57BL/6 mice (recipients). Four weeks later, memory CD4⁺ T cells (CD4⁺Tm) were isolated from the recipient mice's spleens. Mixed lymphocyte reaction experiment was conducted with C57BL/6 mouse splenocytes and CD4⁺Tm, and the EdU method was used to detect the effect of Stattic on CD4⁺Tm cell proliferation. A C57BL/6 mouse heart transplant (HTx) model was constructed, and the experiment was divided into four groups: Non-HTx group, HTx group, Tm/HTx group, and Tm/HTx+Stattic group. The survival of heart allografts in mice was observed daily. Hematoxylin-eosin staining was used to observe the histopathology of the heart allografts. Real-time fluorescent quantitative polymerase chain reaction was used to detect the expression levels of interferon (IFN)-γ, interleukin (IL)-2, IL-10, and transforming growth factor-β1 (TGF-β1) messenger RNA (mRNA) in the heart allografts. Enzyme-linked immunosorbent assay was used to detect the levels of IFN-γ, IL-2, IL-10, and TGF-β1 in the serum. Flow cytometry was used to detect the levels of CD4⁺Tm (CD4⁺CD44⁺CD62L⁺) in splenic lymphocytes. And Western blotting was used to detect the expression levels of STAT3 and p-STAT3 proteins in the heart allografts.

Results When the concentration of Stattic exceeded 2.5 μmol/L, it could inhibit the proliferation of CD4⁺Tm cells. Compared with the HTx group, the Tm/HTx group showed shorter survival time of heart grafts, more severe histopathological damage, increased serum IFN-γ and IL-2 levels, decreased IL-10 and TGF-β1 levels, increased relative expression of IFN-γ and IL-2 mRNA, decreased relative expression of IL-10 and TGF-β1 mRNA in the heart allografts, increased proportion of CD4⁺Tm in splenic lymphocytes, and increased p-STAT3/STAT3 ratio in the heart allografts (all P<0.05). Compared with the Tm/HTx group, the Tm/HTx+Stattic group showed longer survival time of heart grafts, less severe histopathological damage, decreased serum IFN-γ and IL-2 levels, increased IL-10 and TGF-β1 levels, decreased relative expression of IFN-γ and IL-2 mRNA, increased relative expression of IL-10 and TGF-β1 mRNA in the heart allografts, decreased proportion of CD4⁺Tm in splenic lymphocytes, and decreased p-STAT3/STAT3 ratio in the heart allografts (all P<0.05).

Conclusions Stattic may prolong the survival time of mouse heart allografts, and its mechanism may be related to the inhibition of CD4⁺Tm- mediated acute rejection.