Short communication Immunomodulation of Lactobacillus pentosus PL11 against Edwardsiella tarda infection in the head kidney cells of the Japanese eel (Anguilla japonica) Biruk Tesfaye Birhanu a, 1 , Joong-Su Lee a, 1 , Seung-Jin Lee a , Su-Hee Choi a , Md. Akil Hossain a , Ji-Yong Park a , Jong-Choon Kim b , Joo-Won Suh c, ** , Seung-Chun Park a, * a Laboratoryof Veterinary Pharmacokinetics and Pharmacodynamics, College of Veterinary Medicine, Kyungpook National University, Daegu, South Korea b Department of Veterinary Toxicology, College of Veterinary Medicine, Chonnam National University, Gwangju, South Korea c Center for Nutraceutical and Pharmaceutical Materials, Division of Bioscience and Bioinformatics, Science Campus, Myongji University, Yongin, South Korea article info Article history: Received 23 November 2015 Received in revised form 23 March 2016 Accepted 19 April 2016 Available online 20 April 2016 Keywords: Edwardsiella tarda Fish Immunomodulation Lactobacillus pentosus PL11 abstract Wild and farm-raised fish can be simultaneously exposed to different types of pathogens in their hab- itats. Hence, it is important to study their effects, whether isolated or in combination. Therefore, the aim of this study was to evaluate the effects of Lactobacillus pentosus PL11 on the transcription of specific cytokine genes related to immune response, using Japanese eel macrophages as an in vitro model. Head kidney leukocytes were isolated from Japanese eels and cell viability was determined using an MTT reagent. In addition, the Griess reagent was used to determine the nitric oxide (NO) production while, an enzyme-linked immunosobent assay (ELISA) and a quantitative polymerase chain reaction (qPCR) were utilized to quantify the level of proinflammatory cytokines. The results of the study indicated that infection by Edwardsiella tarda alone causes a higher rate of cell death and an increase in the production of proinflammatory cytokines, such as interleukin-1b (IL-1b, 822.67 ± 29.48 pg mL 1 ), interleukin-6 (IL- 6, 13.57 ± 0.55 pg mL 1 ), and tumor necrosis factor-a (TNF-a, 2033.67 ± 84.68 pg mL 1 ). However, co- culture with L. pentosus PL11 downregulates the production of NO and the related IL-1b, IL-6, and TNF-a by 46%, 88.4%, 59%, and 77%, respectively. Quantification of the mRNA expression level revealed it to be consistent with the ELISA analysis. Hence, we infer that L. pentosus PL11 plays a significant role in the immunmodulation of the inflammatory responses that arise in fish owing to infection by pathogenic bacteria such as Edwardsiella tarda. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Innate immune defense mechanisms are activated by the entrance of any foreign elements, such as pathogenic bacterial agents, into a host. In most species of animals, including fish, various types of cells from the immune system, mediate these re- sponses. Macrophages are cells that play a significant role in the immune defense mechanism. They help to regulate both the innate and the acquired immune responses by clearing microbial agents, foreign substances, and dead cells [1,2]. They are actively engaged in phagocytosis, antigen processing, the production of antimicro- bial and anti-tumor agents, and the secretion of various types of mediators, such as NO and reactive oxygen species (ROS). Furthermore, macrophages take part in the inflammatory re- sponses by producing chemokines and pro-inflammatory cyto- kines, such as interleukin-1beta (IL-1b), interleukin-6 (IL-6), and tumor necrosis factor-a (TNF-a). Although the involvement of these proinflammatory cytokines in protecting the body is vital, their over-secretion can also cause some toxic or harmful effects on the host cells [3e5]. The measurement of the expressed mRNA of numerous fish cytokine genes is recognized as a tool for determining their * Corresponding author. Tel.: þ82 53 950 5964. ** Corresponding author. Tel.: þ82 31 330 6881; fax: þ82 31 321 7361. E-mail addresses: jwsuh@mju.ac.kr (J.-W. Suh), parksch@knu.ac.kr (S.-C. Park). 1 Both authors have contributed equally for first authorship. Contents lists available at ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi http://dx.doi.org/10.1016/j.fsi.2016.04.023 1050-4648/© 2016 Elsevier Ltd. All rights reserved. Fish & Shellfish Immunology 54 (2016) 466e472