Elicitation of T-cell responses by structural and non-structural proteins of coxsackievirus B4

Induction of immune responses by a novel recombinant fusion protein of enterovirus A71 in BALB/c mice

Fusion protein technology is used in biotechnology and medical developments. In this study, recombinant fusion proteins from enterovirus A71 (EV-A71) subgenotype B5, Thailand were designed based two surface proteins (VP1 and VP2) and an internal protein (VP4), and named "VP0" (consisting of VP4-VP2) and "EV71" (consisting of VP4-VP2-VP1), respectively. The recombinant fusion proteins VP0 and EV71 were expressed in insect cells and successfully produced and secreted into the media. Both recombinant fusion proteins were shown to have immunogenic properties in BALB/c mice when formulated with Freund's complete/incomplete adjuvant (FA). Interestingly, EV71 formulated with FA- induced a level of IgG antibodies level similar to that induced by the recombinant protein VP1 formulated with FA (the positive control). Our results showed that VP1 alone is better at eliciting a strong cell-mediated immune response. Nontheless, EV71 formulated with FA was capable of inducing lymphocyte proliferation and increasing the cytokine-related mRNA expression levels of interferon-γ (IFN-γ), interleukin-2 (IL-2), and IL-10 in mice after immunization. Additionally, the number of CD4⁺ and CD8⁺ T lymphocyte cells after stimulation with purified EV71 in splenic cell culture showed highly specific CD4⁺ and CD8⁺ T-cell production. We suggest that EV71, which consists of VP4-VP2-VP1, could be used as the foundation for developing a novel recombinant fusion protein-based vaccine for EV-A71.

Adaptive Immune Responses following Senecavirus A Infection in Pigs

Senecavirus A (SVA), an emerging picornavirus of swine, causes vesicular disease (VD) that is clinically indistinguishable from foot-and-mouth disease (FMD) in pigs. Many aspects of SVA interactions with the host and the host immune responses to infection, however, remain unknown. In the present study, humoral and cellular immune responses to SVA were evaluated following infection in pigs. We show that SVA infection elicited an early and robust virus-neutralizing (VN) antibody response, which coincided and was strongly correlated with VP2- and VP3-specific IgM responses. Notably, the neutralizing antibody (NA) responses paralleled the reduction of viremia and resolution of the disease. Analysis of the major porcine T-cell subsets revealed that during the acute/clinical phase of SVA infection (14 days postinfection [p.i.]), T-cell responses were characterized by an increased frequency of αβ T cells, especially CD4⁺ T cells, which were first detected by day 7 p.i. and increased in frequency until day 14 p.i. Additionally, the frequency of CD8⁺ and double-positive CD4⁺ CD8⁺ T cells (effector/memory T cells) expressing interferon gamma (IFN-γ) or proliferating in response to SVA antigen stimulation increased after day 10 p.i. Results presented here show that SVA elicits B- and T-cell activation early upon infection, with IgM antibody levels being correlated with early neutralizing activity against the virus and peak B- and T-cell responses paralleling clinical resolution of the disease. The work provides important insights into the immunological events that follow SVA infection in the natural host.IMPORTANCE Senecavirus A (SVA) has recently emerged in swine, causing outbreaks of vesicular disease (VD) in major swine-producing countries around the world, including the United States, Brazil, China, Thailand, and Colombia. Notably, SVA-induced disease is clinically indistinguishable from other high-consequence VDs of swine, such as FMD, swine vesicular disease, vesicular stomatitis, and vesicular exanthema of swine. Despite the clinical relevance of SVA-induced VD, many aspects of the virus infection biology remain unknown. Here, we assessed host immune responses to SVA infection. The results show that SVA infection elicits early B- and T-cell responses, with the levels of VN antibody and CD4⁺ T-cell responses paralleling the reduction of viremia and resolution of the disease. SVA-specific CD8⁺ T cells are detected later during infection. A better understanding of SVA interactions with the host immune system may allow the design and implementation of improved control strategies for this important pathogen of swine.