Th1-biased immunoadjuvant effect of the recombinant B subunit of an <i>Escherichia coli</i> heat-labile enterotoxin on an inactivated porcine reproductive and respiratory syndrome virus antigen via intranasal immunization in mice

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is one of the major swine diseases responsible for a significant challenge in the global swine industry. The current PRRS inactivated vaccine only confers limited protection against PRRSV. Thus, using an appropriate adjuvant via a suitable administration route may help improve vaccine efficacy. In this study, the recombinant B subunit of the Escherichia coli heat-labile enterotoxin rLTB, was highly expressed in Pichia pastoris, through high-density fermentation. rLTB intranasal adjuvant properties were evaluated on an inactivated PRRS antigen in mice. Compared to the group immunized with solely PRRS antigen, a dose of 50 µg rLTB remarkably raised antigen-specific IgA antibodies at mucosal sites, and increased serum IgG antibodies, preferentially the IgG2a and IgG2b subclasses. Further, rLTB induced increases in Th1- (IFN-γ and IL-12) and Th17 (IL-6) cytokine profiles, but had little effect on Th2 cytokine profiles (IL-4 and IL-10). Moreover, there were no overt toxicities associated with intranasal rLTB administration. Our data provide evidence that the rLTB produced by P. pastoris fermentation portrays low toxicity, and its intranasal adjuvant effect involves immune system modulation to a Th1 profile.

Escherichia coli Heat-Labile Enterotoxin B Subunit Combined with Ginsenoside Rg1 as an Intranasal Adjuvant Triggers Type I Interferon Signaling Pathway and Enhances Adaptive Immune Responses to an Inactivated PRRSV Vaccine in ICR Mice

“…As reported in earlier research, PRRSV-infected pigs typically show insufficient Th1-type immune responses, leading to prolonged immunosuppression [ 46 ]. Administration of 50 µg/mouse dose of LTB enhanced the PRRSV-specific immune response skewed toward Th1 production, as previously observed [ 19 ]. Notably, in the current study, LTB combined with Rg1 significantly enhanced both IgG1 and IgG2a responses, a finding that may be correlated with the increased numbers of IFN-γ- and IL-10- producing CD4 + T cells and up-regulated IFN-γ, IL-2, IL-5, and IL-10 responses in the spleen and lung tissues.…”

“…Even though LTB has been used widely as an adjuvant [ 19 , 31 , 32 ], IN administration of LTB has not overcome the major limitation of transient adverse effects (Bell’s palsy) in humans [ 33 ]. Earlier studies in animal models did not indicate any adverse effects in laboratory animals [ 11 ] and demonstrated that IN administration of nontoxic LT was safe without any pathological changes in the nasal mucosa of mice 3 days after administration [ 34 , 35 ].…”

“…Recombinant LTB was produced by the GS115 strain of Pichia pastoris as previously described [ 19 ]. Ginsenosides Rg1 extracted from the root of Panax ginseng was purchased from Biopurify Co. Ltd. (Chengdu, China).…”

“…PRRSV-specific IgA, IgG, IgG1, and IgG2a antibodies were measured by indirect enzyme-linked immunosorbent assays (ELISA) [ 19 ]. Briefly, polyvinyl 96-well microplates pre-coated with PRRSV antigen were obtained from IDEXX PRRS X3 ELISA kits (IDEXX, Westbrook, USA).…”

“…Previous studies have suggested that GM1-binding activity is a necessary but not the only mechanism for LTB adjuvanticity [ 17 , 18 ]. Our previous work has demonstrated that LTB serves as a nasal adjuvant of an inactivated PRRSV vaccine by enhancing PRRSV-specific immune responses to Th1 type (T helper type 1) cells in mice [ 19 ]. Nevertheless, a Th1/Th2 balanced immunity is more desirable to provide potent and broad protection against pathogen invasion.…”