Flowing differently: exploratory characterization of menstrual effluent compared with peripheral blood.

ObjectiveTo characterize the immune cell and hormonal profile of menstrual effluent compared with paired peripheral blood.DesignThis descriptive, cross-sectional study collected menstrual effluent and processed it to isolate cellular and soluble fractions; peripheral blood was processed in parallel. Steroid hormones were quantified using immunoassays, immune cell populations were assessed by multiparameter flow cytometry, and cytokines and chemokines were measured using multiplex assays.SubjectsMenstrual effluent and peripheral blood were collected from 13 healthy participants (excluding those using NSAIDs or hormonal contraception) after informed consent.ExposureNone MAIN OUTCOME MEASURES: The immune cell and hormonal profiles of menstrual effluent and peripheral blood were the main outcome measures.ResultsProgesterone and cortisol concentrations were significantly decreased in menstrual effluent compared with peripheral blood. Menstrual effluent exhibited distinct immune and cytokine profiles, including increased plasmacytoid and myeloid dendritic cells, neutrophils, natural killer (NK) cells, and memory CD8+ T cells, alongside decreased regulatory T cells, natural killer T (NKT) cells, and multiple B cell subsets. Cytokine analysis revealed multiple elevated cytokines in menstrual effluent, even after false discovery rate correction.ConclusionsMenstrual effluent is immunologically and hormonally distinct from peripheral blood, which may reflect inflammatory and tissue-repair activity. These findings contribute to the understanding of the normative baseline for menstrual effluent.