{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,20]],"date-time":"2026-08-20T14:58:53Z","timestamp":1787237933642,"version":"build-2736575974"},"reference-count":22,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,1,29]],"date-time":"2026-01-29T00:00:00Z","timestamp":1769644800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Microorganisms"],"abstract":"<jats:p>Heat-killed Enterococcus faecalis EF-2001 (EF-2001) is a postbiotic preparation reported to modulate host immunity. However, its specific impact on host immune responses and virological outcomes during the early phase of influenza infection remains insufficiently characterized. Female BALB\/c mice received oral EF-2001 (16 mg\/kg\/day) for either 4 days or 14 days prior to intranasal inoculation with influenza A\/H3N2 (A\/Aichi\/2\/68). On day 2 post-infection, splenic T-cell subsets (CD3+, CD4+, CD8+) were quantified by flow cytometry. Cytokines released from PMA\/ionomycin-stimulated splenocytes were measured using a cytometric bead array assay to assess functional polarization. Lung viral titers (TCID50) and interferon-\u03b1 (IFN-\u03b1) concentrations were assessed to evaluate local antiviral efficacy. EF-2001 administration significantly increased the proportions of splenic CD3+ T cells, including both CD4+ and CD8+ subsets, compared to controls. The 14-day pretreatment regimen significantly enhanced IFN-\u03b3 production while reducing IL-10, IL-4, and IL-2 secretion, consistent with a distinct systemic Th1-skewed immune activation. In contrast to these systemic effects, EF-2001 did not significantly reduce lung viral titers (difference &lt; 0.2 log10 TCID50) and did not increase lung IFN-\u03b1 concentrations at day 2 post-infection. Oral EF-2001 pretreatment promoted systemic immune activation characterized by T-cell expansion and a Th1-biased cytokine profile. However, this systemic priming showed no detectable antiviral effect on lung viral burden at the early evaluation time point. EF-2001 may be better positioned as an adjunctive immunomodulatory approach rather than a direct antiviral agent, warranting further studies that include clinical outcomes and multi-time-point antiviral and mucosal immune assessments.<\/jats:p>","DOI":"10.3390\/microorganisms14020316","type":"journal-article","created":{"date-parts":[[2026,1,29]],"date-time":"2026-01-29T10:56:34Z","timestamp":1769684194000},"page":"316","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Heat-Killed Enterococcus faecalis EF-2001 Promotes Systemic Th1-Skewed Immune Activation Without Detectable Reduction of Influenza Viral Load in Mice"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3473-4251","authenticated-orcid":false,"given":"Takahisa","family":"Ohashi","sequence":"first","affiliation":[{"name":"Department of Clinical Infectious Diseases, Aichi Medical University Graduate School of Medicine, Nagakute 480-1195, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mao","family":"Hagihara","sequence":"additional","affiliation":[{"name":"Department of Clinical Infectious Diseases, Aichi Medical University Graduate School of Medicine, Nagakute 480-1195, Japan"},{"name":"Department of Molecular Epidemiology and Biomedical Sciences, Aichi Medical University, Nagakute 480-1195, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nobuhiro","family":"Asai","sequence":"additional","affiliation":[{"name":"Department of Clinical Infectious Diseases, Aichi Medical University, Nagakute 480-1195, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuka","family":"Yamagishi","sequence":"additional","affiliation":[{"name":"Department of Clinical Infectious Diseases, Aichi Medical University Graduate School of Medicine, Nagakute 480-1195, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8876-6411","authenticated-orcid":false,"given":"Hiroshige","family":"Mikamo","sequence":"additional","affiliation":[{"name":"Department of Clinical Infectious Diseases, Aichi Medical University Graduate School of Medicine, Nagakute 480-1195, Japan"},{"name":"Department of Clinical Infectious Diseases, Aichi Medical University, Nagakute 480-1195, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Choi, E.-J., Lee, H.J., Kim, W.-J., Han, K.-I., Iwasa, M., Kobayashi, K., Debnath, T., Tang, Y., Kwak, Y.-S., and Yoon, J.-H. 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