OBJECTIVES: This study investigates whether latent Epstein-Barr virus (EBV) can be reactivated by n-butyric acid from Pseudoramibacter alactolyticus, and if such reactivation induces expression of interleukin (IL)-1β and IL-6 in periapical granulomas. METHODS: We analyzed periapical granulomas and healthy gingival tissues to detect the presence of EBV and P. alactolyticus. The concentration of n-butyric acid in P. alactolyticus culture supernatants was measured. BZLF-1 luciferase assays were conducted with or without these supernatants. Immunohistochemical detection of ZEBRA-, IL-1β-, and IL-6-expressing cells was performed in the tissue samples. Additionally, mRNA expression levels of BZLF-1, IL-1β, and IL-6 were quantified and statistically analyzed for correlation. The expression of these mRNAs was also measured in Daudi cells treated with or without the culture supernatants. RESULTS: Both EBV and P. alactolyticus were detected in periapical granulomas, but not in healthy tissues. The concentration of n-butyric acid in the culture supernatants was ∼3.58 mmol/L. BZLF-1 luciferase activity in the presence of the culture supernatants was comparable to that of commercially available butyric acid, whereas no activity was detected without the supernatants. Cells expressing ZEBRA co-expressed IL-1β and IL-6. The mRNA levels of IL-1β and IL-6 in periapical granulomas were correlated with BZLF-1 mRNA levels. Daudi cells treated with the culture supernatants expressed BZLF-1, IL-1β, and IL-6 mRNA, while those without the supernatants did not. CONCLUSIONS: The study concludes that EBV can be reactivated by n-butyric acid produced by P. alactolyticus, leading to the induction of IL-1β and IL-6 expression in periapical granulomas.