Abstract: Objective In this study, we constructed different strains of EHEC O157: H7 (wild strain and mutant strains) to infect THP-1 cells in order to study the toxicity of different strains and cytokine production levels, such as IL-1β, and also compare the THP-1-secreted cytokine levels under the conditions of being cultured with or without FBS after infected with EHEC. Methods Aliquots of the bacteria were added in triplicate to the cell monolayer. At 2-10 h after infection, the release of lactate dehydrogenase (LDH) was quantified by using a Cytotox96 Kit. Meanwhile, the levels of human cytokines were quantified by using a Luminex Kit and ELISA Kit. Results Our results demonstrated that EHEC O157:H7-ehxA contributed to cytotoxicity in THP-1 cells, causing the production of higher IL-1β. Most important, the results showed that the cells cultured in 5% FBS-containing RPMI 1640 medium produced higher IL-1β while the difference in IL-1β level between wild type strains and mutant strains was more significant in OPT1-MEM serum-free medium. Conclusion ehxA plays a crucial role in EHEC O157:H7-induced IL-1β production. Moreover, the result revealed that the serum could stimulate cells to produce small amount of non specific IL-1β, which might cause the high background and hide the real difference between strains.