Incorporation of a bi-functional protein FimH enhances the immunoprotection of chitosan-pVP1 vaccine against coxsackievirus B3-induced myocarditis.

Viral myocarditis is a common clinical cardiovascular disease mainly induced by coxsackievirus B3 (CVB3) with no effective therapeutic measures. Induction of efficient mucosal immune responses is very critical against CVB3-induced myocarditis. FimH is an Escherichia coli (E. coli)-derived protein, which possesses an M cell-targeting property and functions as a TLR4 agonist. In this study, we introduced the recombinant FimH protein, into our previously developed CVB3 mucosal vaccine chitosan (CS)-pVP1, aiming to provoke more efficient mucosal immune responses and immunoprotection against CVB3-induced myocarditis. Compared with the CS-pVP1 vaccine, immunization with FimH-CS-pVP1 remarkably increased the levels and neutralizing titers of CVB3-specific protective secretory IgA (sIgA), enhanced the frequency of CVB3-specific IgA-producing B cells and amplified mucosal T-cell immune responses in mesenteric lymph nodes (MLNs), although failing to significantly amplify CVB3-specific systemic immune responses. Consistently, FimH-CS-pVP1 group showed the enhanced immunoprotection against CVB3-induced myocarditis, evidenced by the indices of limited myocardial injury, reduced viral loads and enhanced survival rate. Further study showed that this enhanced immunoprotection was not only ascribed to its M cell-targeting property, which led to the enhanced mucosal antigen VP1 expression, but also associated with the mucosal adjuvant effect of FimH, which facilitated the formation of germinal centers (GCs), production of IgA-inducing factors and maturation of antigen-presenting cells (APCs). Taken together, here we developed a bi-functional mucosal vaccine FimH-CS-pVP1, which simultaneously possessed the M cell-targeting property and mucosal adjuvant ability, and we showed that FimH-CS-pVP1 could efficiently induce the higher levels of CVB3-specific protective mucosal immune responses and provide better prophylactic effects against CVB3-induced myocarditis than CS-pVP1.