Immunomodulatory Effects of Tokishakuyakusan on Progesterone Withdrawal-Induced Uterine Inflammation in Pregnant Mice.

PROBLEM: Tokishakuyakusan (TSS) is a traditional Japanese Kampo medicine widely used to support pregnancy; however, its molecular mechanisms remain poorly understood. This study aimed to elucidate the progesterone-related immunomodulatory mechanisms underlying the pregnancy-supportive effects of TSS using a mouse model of progesterone withdrawal induced by mifepristone. METHODS: Pregnant mice were fed either a control diet or a diet containing 1% TSS from mating until late gestation. On day 15 postcoitus, all mice received low-dose mifepristone to induce functional progesterone withdrawal. Cytokine and chemokine profiles in serum, corpus uteri, and placenta were analyzed using multiplex assays, and uterine expression of progesterone-responsive and inflammatory genes were evaluated by real-time RT-PCR. RESULTS: Mifepristone administration induced a systemic proinflammatory response, characterized by increased serum levels of G-CSF, IL-6, KC, and MCP-1. TSS administration increased G-CSF without affecting fetal number, fetal weight, or placental weight. In the corpus uteri, TSS significantly suppressed IL-6 protein expression, whereas placental cytokine profiles were largely unaffected. Furthermore, TSS significantly increased uterine mRNA expression of the progesterone-responsive anti-inflammatory molecules secretory leukocyte peptidase inhibitor (SLPI) and progranulin (PGRN). CONCLUSIONS: These findings suggest that TSS mitigates inflammation associated with progesterone withdrawal by suppressing uterine IL-6 and increasing the expression of progesterone-responsive anti-inflammatory molecules such as SLPI and PGRN. These findings suggest that TSS may modulate progesterone-responsive anti-inflammatory pathways through increased expression of SLPI and PGRN while suppressing uterine IL-6.