A Review of Intra- and Extracellular Antigen Delivery Systems for Virus Vaccines of Finfish

Abstract

Vaccine efficacy in aquaculture has for a long time depended on evaluating relative percent survival and antibody responses after vaccination. However, current advances in vaccine immunology show that the route in which antigens are delivered into cells is deterministic of the type of adaptive immune response evoked by vaccination. Antigens delivered by the intracellular route induce MHC-I restricted CD8+ responses while antigens presented through the extracellular route activate MHC-II restricted CD4+ responses implying that the route of antigen delivery is a conduit to induction of B- or T-cell immune responses. In finfish, different antigen delivery systems have been explored that include live, DNA, inactivated whole virus, fusion protein, virus-like particles, and subunit vaccines although mechanisms linking these delivery systems to protective immunity have not been studied in detail. Hence, in this review we provide a synopsis of different strategies used to administer viral antigens via the intra- or extracellular compartments. Further, we highlight the differences in immune responses induced by antigens processed by the endogenous route compared to exogenously processed antigens. Overall, we anticipate that the synopsis put together in this review will shed insights into limitations and successes of the current vaccination strategies used in finfish vaccinology.

B cells and their role in the teleost gut

“…As a result, most of the immune responses analyzed in intestine regarding B cells and immunoglobulins are limited to IgM, while very few studies have focused on IgT, and none on IgD. Most of the examined immune responses in intestine, and in mucosal tissues in general, have been obtained after mucosal vaccination with different pathogens (Munang’andu and Evensen, 2015; Mutoloki et al, 2015). It is important to point out that the immune response in the gut will present great variability among the teleosts, depending on the pathogen, fish species, region of the intestine selected for study, and even the microbiota in the environment, or diet.…”

An Overview of Vaccination Strategies and Antigen Delivery Systems for Streptococcus agalactiae Vaccines in Nile Tilapia (Oreochromis niloticus)

“…These vaccines are considered safe because they are “killed” and as such, they pose no danger of reversion to virulence [6]. They require the help of adjuvants to enhance their immunogenicity [7,30]. Different adjuvants have been used in IWC-vaccine formulations for S. agalactiae in tilapia and these include Freund’s incomplete [22,28] and aluminum hydroxide gel (AH) [22] adjuvants.…”

Edwardsiella tarda OmpA Encapsulated in Chitosan Nanoparticles Shows Superior Protection over Inactivated Whole Cell Vaccine in Orally Vaccinated Fringed-Lipped Peninsula Carp (Labeo fimbriatus)

“…Although different NP vaccines have been used in aquaculture [18,19,52,53,54], few studies have evaluated their ability to release the antigens in vitro [55,56]. It is important that the ability of the NPs to release antigens in vitro be evaluated as this would give insight into their ability to induce a protective immune response in vaccinated fish.…”