Coxsackievirus B3 (CVB3), a small single-stranded RNA virus, belongs to the Picornaviridae family. Its infection is the most common cause of myocarditis, with no vaccine available. Gastrointestinal mucosa is the major entry port for CVB3; therefore, the induction of local immunity in mucosal tissues may help control initial viral infections and alleviate subsequent myocardial injury. Here we evaluated the ability of high-mobility group box 1 (HMGB1) encapsulated in chitosan particles to enhance the mucosal immune responses induced by the CVB3-specific mucosal DNA vaccine chitosan-pVP1. Mice were intranasally coimmunized with 4 doses of chitosan-pHMGB1 and chitosan-pVP1 plasmids, at 2-week intervals, and were challenged with CVB3 4 weeks after the last immunization. Compared with chitosan-pVP1 immunization alone, coimmunization with chitosanpHMGB1 significantly (P < 0.05) enhanced CVB3-specific fecal secretory IgA levels and promoted mucosal T cell immune responses. In accordance, reduced severity of myocarditis was observed in coimmunized mice, as evidenced by significantly (P < 0.05) reduced viral loads, decreased myocardial injury, and increased survival rates. Flow cytometric analysis indicated that HMGB1 enhanced dendritic cell (DC) recruitment to mesenteric lymph nodes and promoted DC maturation, which might partly account for its mucosal adjuvant effect. This strategy may represent a promising approach to candidate vaccines against CVB3-induced myocarditis.C oxsackieviruses belong to the Picornaviridae family with single-stranded RNA genomes and are implicated in various clinical manifestations, ranging from mild to severe life-threatening diseases (1-3). Among them, coxsackievirus B3 (CVB3) is considered to be the most common cause of viral myocarditis (4). Previous studies showed that about 5 to 50% of cases of myocarditis and its end stage of dilated cardiomyopathy, as well as congestive heart failure, are attributable to CVB3 infection (5-7). Although a few vaccine candidates have been reported to be effective in a murine CVB3-induced myocarditis model (8-10), no prophylactic or therapeutic reagent is available for the clinic to date. Thus, development of new efficient vaccines is needed urgently.Various types of CVB-specific vaccines have been examined in animal models, including inactivated or attenuated virus vaccines (11, 12), recombinant protein vaccines (13), DNA vaccines (14), and virus-like particle vaccines (8). Considering that CVB3 mainly invades hosts through the gastrointestinal tract, it is critical to induce mucosal immune responses to limit virus infection in the initial stage and at the primary site.Compared with other candidates, mucosal vaccines are more likely to induce immune tolerance rather than activation, due to their limited immunogenicity and the special mucosal environment. Therefore, discovery of safe effective mucosal adjuvants is critical to the success of mucosal vaccines. High-mobility group box 1 (HMGB1), also known as amphoterin, was originally identified as a highly ...