BACKGROUND: Methylprednisolone (MP) can affect the survival of CD4 + T lymphocytes and plays an important role in adaptive immune responses; however, its mechanism of action is not clear. Recent studies have shown that toll- like receptors (TLRs) on CD4 + T cells can directly modulate adaptive immune responses by affecting the survival and proliferation of activated CD4 + T cells. This study aimed to investigate the relationship between MP, TLRs and activated CD4 + T cells. METHODS: We separated and purified CD4 + T cells from mice, activated them in vitro, and co-cultured them with TLR ligands, MP or inhibitors of nuclear factor-kappa B (NF-κB) and activator protein 1 (AP-1). We then assessed CD4 + T cell survival and proliferation and the expression of NF-κB and AP-1. RESULTS: Activated CD4 + T cells showed increased TLR-3 and TLR-9 mRNA expression, but polyinosinic-polycytidylic acid (poly I:C) and MP had no effect on the expression of these mRNAs. Still, poly I:C and CpG oligodeoxynucleotides (CpG DNA) increased the survival of activated CD4 + T cells whereas MP reduced the survival of activated CD4 + T cells and could inhibit the survival effects of poly I:C and CpG DNA. The NF-κB essential modifier-binding domain (NBD) inhibited the survival of activated CD4 + T cells induced by poly I:C and CpG DNA, but the AP-1 inhibitor crucumin did not have the same effect. The increased expression of NF-κB induced by poly I:C and CpG DNA in activated CD4 + T cells could be inhibited by MP, but the same was not true for the increased expression of AP-1 induced by poly I:C and CpG DNA. Finally, the proliferation of activated CD4 + T cells was not affected by poly I:C or MP. CONCLUSION: The survival of activated CD4 + T cells is promoted by TLR ligands, but this effect is inhibited by MP. BACKGROUND: Methylprednisolone (MP) can affect the survival of CD4 + T lymphocytes and plays an important role in adaptive immune responses; however, its mechanism of action is not clear. Recent studies have shown that toll- like receptors (TLRs) on CD4 + T cells can directly modulate adaptive immune responses by affecting the survival and proliferation of activated CD4 + T cells. This study aims to investigate the relationship between MP, TLRs and activated CD4 + T cells. METHODS: We separated and purified CD4 + T cells from mice, activated them in vitro, and co-cultured them with TLR ligands, MP or inhibitors of nuclear factor-kappa B (NF-κB) and activator protein 1 (AP-1). We then assessed CD4 + T cell survival and proliferation RESULTS: Activated CD4 + T cells showed increased TLR-3 and TLR-9 mRNA expression, but polyinosinic-polycytidylic acid (poly I: C) and MP had no effect on the expression of these mRNAs. Still, poly I: C and CpG oligodeo xynucleotides (CpG DNA) increased the survival of activated CD4 + T cells while MP reduced the survival of activated CD4 + T cells and could inhibit the survival effects of poly I: C and CpG DNA. The NF-κB essential modifier-binding domain NBD) inhibited the survival of activated CD4 + T cells induced by poly I: C and CpG DNA, but the AP-1 inhibitor crucumin did not have the same effect. DNA in activated CD4 + T cells could be inhibited by MP, but the same was not true for the increased expression of AP-1 induced by poly I: C and CpG DNA. Finally, the proliferation of activated CD4 + T cells was not affected by poly I: C or MP. CONCLUSION: The survival of activated CD4 + T cells is promoted by TLR ligands, but this effect is inhibited by MP.