Treatment with NK33 and/or NK98, which were orally gavaged in mice before or after IS treatment, significantly suppressed the occurrence and development of anxiety/depression, infiltration of Iba1+ and LPS+/CD11b+ cells (activated microglia) into the hippocampus, and corticosterone, IL-6, and LPS levels in the blood. The gene discussed is IL6; the disease is depressive disorder.