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

Abstract

ABSTRACT 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.