5,2'-Dibromo-2,4,5-trihydroxydiphenylmethanone, a novel immunomodulator of T lymphocytes by regulating the CD4+ T cell subset balance via activating the mitogen-activated protein kinase pathway.

5,2'-Dibromo-2,4',5'-trihydroxydiphenylmethanone (LM49) exerted therapeutic effects against rat acute pyelonephritis by regulating immune responses, especially affecting T lymphocytes. However, its underlying action mechanism remains unclear. T lymphocytes play an irreplaceable role in immune responses. Therefore, we sought to understand whether LM49 is an immunomodulator of T lymphocytes. The results showed that LM49 promoted T lymphocyte proliferation, increased the number of CD4+ T cells, and increased the CD4+/CD8+ T cell ratio. LM49 regulated the CD4+ T cell subset balance by increasing the production of CD4+IL-2+, CD4+IL-4+, and CD4+IL-10+, and reducing the production of CD4+IL-17+, without changing the production of interferon-γ. LM49 had a significant effect on the mRNA expression of the transcription factors T-bet, GATA3, Foxp3, and RORγt. Furthermore, LM49 raised the phospho (p)-extracellular signal-regulated protein kinase 1/2, p-p38, and p-c-Jun N-terminal kinase expression levels. T cell proliferation, and the production of CD4+IL-2+, CD4+IL-4+, and CD4+IL-10+ induced by LM49, were decreased by inhibitors of mitogen-activated protein kinases (MAPKs). These results revealed that LM49 possesses immunomodulatory activity on T lymphocytes, in which the MAPK pathway plays an essential role.