en Original article Original article <p> <strong> Background: </strong><strong></strong>Nanoparticles have been considered as promising tools because of their high applicability. Recently, nanoparticles have been evaluated for their ability to increase the immune responses as adjuvants.<a name="OLE_LINK10"></a><a name="OLE_LINK9"> Silver-nanoparticles (AgNPs) </a>have shown promising results in enhancing Th-2 immune responses and to produce potent neutralizing antibodies. Neutralizing antibodies are considered as the main defense mechanism in pre- and post-exposure treatments of rabies disease. Therefore in this study, the effects of AgNPs in enhancing the immunogenicity of inactivated rabies virus were assessed.<strong> Materials and Methods:</strong> Different concentrations of AgNPs (0.2, 0.4, 0.6 and 0.8 mg/ml) were added to inactivated rabies virus. Mice were immunized by two intra-peritoneal injections of each concentration on days 1 and 7. The inactivated virus and Alum were used as negative and positive controls, respectively. Blood was collected from healthy and immunized mice, one week after the last immunization. Serum was isolated from each sample and the amounts of neutralizing antibodies were determined by Rapid Florence Focus Inhibition Test (RFFIT). The <a name="OLE_LINK28"></a><a name="OLE_LINK27">cytotoxicity </a>of AgNPs was also assessed by <i>in vitro</i> MTT assay on J774A.1 cell line.<strong> Results:</strong> The results showed that 0.4, 0.6 and 0.8 mg/ml of AgNPs had significantly increased the immune responses compared to the control however, 0.2 mg/ml of AgNPs did not show a significant effect. No cytotoxicity was observed for 0.001 and 0.01 mg/ml concentrations of AgNPs but cell viability was decreased significantly at 0.1 mg/ml concentration.<strong> Conclusion:</strong> It was shown that the virus-loaded AgNPsat 0.4 mg/ml concentration could raise the neutralizing antibodies against rabies virus in mice, but their adverse effect on cell viability excludes their use as an adjuvant. <i>Vac Res</i> <i>, 2014, 1 (1): 32-35</i>  </p> Adjuvant, Silver Nanoparticle, Rabies Vaccine, Neutralizing Antibodies 31 34 http://vacres.pasteur.ac.ir/browse.php?a_code=A-10-27-5&slc_lang=en&sid=1 Vahid Asgary No Department of Rabies, Virology Research Group, Pasteur Institute of Iran, Tehran, Iran, Department of Immunology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Omid Kord Mafi No Department of Biotechnology, Payam-e-Nour University, East Branch, Tehran, Iran Mohammad Sadeq Khosravy No Department of Laboratory of Animal Sciences, Pasteur Institute of Iran, Tehran, Iran Alireza Janani No Department of Rabies, Virology Research Group, Pasteur Institute of Iran, Tehran, Iran Nabiollah Namvar Asl No Department of Laboratory of Animal Sciences, Pasteur Institute of Iran, Tehran, Iran Rouzbeh Bashar No Department of Rabies, Virology Research Group, Pasteur Institute of Iran, Tehran, Iran Hadi Poortaghi No Faculty of Veterinary Medicine, Islamic Azad University, Karaj, Iran Hossein Ahangari Cohan No Faculty of Veterinary Medicine, Islamic Azad University, Karaj, Iran Alireza Shoari No Department of Molecular and Cellular Biology, Islamic Azad University, Pharmaceutical Sciences Branch, Tehran, Iran Reza Ahangari Cohan Cohan_r@yahoo.com Yes Department of Rabies, Virology Research Group, Pasteur Institute of Iran, Tehran, Iran