en Vaccine vectors, adjuvantsand immunomodulators Vaccine vectors, adjuvantsand immunomodulators Original article Original article <strong>Introduction: </strong>Avian influenza virus causes severe economic losses to the poultry industry and has a great potential for becoming a pandemic threat for humans. The application of natural adjuvants has opened up new avenues toward reaching a highly efficient and safe vaccine in recent years.&nbsp; In this study, we investigated the adjuvant activity of interferon-induced myxovirus resistance (Mx) protein on chitosan-based H9N2 nanoparticles in a BALB/c mouse model. <strong>Methods:</strong> The inactivated H9N2 virus antigen was encapsulated in chitosan nanoparticles (NPs) using gelation method. Female BALB/c mice were randomly divided into four groups (n=10). Group A received the H9N2-loaded chitosan NPs mixing with Mx intranasally and was boosted twice with a 1-week interval. Group B received the H9N2-loaded chitosan NPs in the same manner. Mice in groups C and D received the chitosan NPs and PBS, respectively as negative controls. Body weights of the mice were measured at defined times. Blood samples were collected from the animals and their influenza-specific antibody titer was determined using ELISA. <strong>Results:</strong> The results demonstrated a higher antibody level in treated groups A and B as compared to the control samples. We also showed that the combination of Mx and chitosan could significantly induce an influenza-specific antibody titer, indicating synergistic effects of the applied adjuvant and NPs together. <strong>Conclusion:</strong> The formulation of H9N2 with Mx as an adjuvant and chitosan as a nanocarrier is a promising procedure for developing an efficient vaccine against avian influenza virus. Avian influenza, Chitosan, Mx, Nanoparticles, Immune responses 34 40 http://vacres.pasteur.ac.ir/browse.php?a_code=A-10-1910-2&slc_lang=en&sid=1 Maryam Ahmadi m.ahmadi@rvsri.ac.ir 0000-0002-6121-6433 No Razi Vaccine and Serum Research Institute, Agricultural Research Education and Extension Organization (AREEO), Karaj, Iran. Gholamreza Hashemi Tabar hashemit@um.ac.ir 0000-0001-9760-1096 Yes Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran Shahla Shahsavandi Shahsavandi26@gmail.com 0000-0002-9599-6722 No Razi Vaccine and Serum Research Institute, Agricultural Research Education and Extension Organization (AREEO), Karaj, Iran. Alireza Haghparast No Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran