Vaccination with Recombinant Baculovirus Expressing Ranavirus Major Capsid Protein Induces Protective Immunity in Chinese Giant Salamander, Andrias davidianus.

The Chinese giant salamander iridovirus (CGSIV), belonging to the genus Ranavirus in the family Iridoviridae, is the causative agent of an emerging infectious disease causing high mortality of more than 90% and economic losses in Chinese giant salamanders in China. In this study, a recombinant baculovirus-based vaccine expressing the CGSIV major capsid protein (MCP) was developed and its protective immunity in Chinese giant salamanders was evaluated. The recombinant Autographacalifornica nucleopolyhedrosis virus (AcNPV), expressing CGSIV MCP, designated as AcNPV-MCP, was generated with the highest titers of 1 × 108 plaque forming units/mL (PFU/mL) and confirmed by Western blot and indirect immunofluorescence (IIF) assays. Western blot analysis revealed that the expressed MCP reacted with mouse anti-MCP monoclonal antibodies at the band of about 53 kDa. The results of IIF indicated that the MCP was expressed in the infected Spodoptera frugiperda 9 (Sf9) cells with the recombinant baculovirus, and the Chinese giant salamander muscle cells also transduced with the AcNPV-MCP. Immunization with the recombinant baculovirus of AcNPV-MCP elicited robust specific humoral immune responses detected by ELISA and neutralization assays and potent cellular immune responses in Chinese giant salamanders. Importantly, the effective immunization conferred highly protective immunity for Chinese giant salamanders against CGSIV challenge and produced a relative percent of survival rate of 84%. Thus, the recombinant baculovirus expressing CGSIV MCP can induce significant immune responses involving both humoral and cell-mediated immunity in Chinese giant salamanders and might represent a potential baculovirus based vaccine candidate for Chinese giant salamanders against CGSIV.

Specific and non-specific immunosuppressive factors in salamander pregnancy serum.

In vitro experiments employing pregnant Salamandra salamandra have previously shown a maternal specific cytotoxic cellular reaction against larval cells and an inhibition of this reaction by maternal serum. Two serum fractions, 19S and 13S, have been implicated in this inhibition. In the present work, the site of action and the identity of the factors responsible for this activity have been determined. Pre-incubation experiments indicate that the 19S fraction from pregnancy serum specifically protects embryonic epithelial cells derived from the same pregnant female. The 13S fraction non-specifically inhibits cytotoxic activity of maternal cells. Both factors implicated in these reactions are respectively an IgM and an alpha 2-macroglobulin. The question of whether the alpha 2M is responsible for immunosuppression is discussed, with particular reference to its vitellogenin analogue and also in view of the fact that the presence of this alpha 2M is not always linked with the immunosuppressive properties (except during pregnancy).

[Inhibition of an immune hemolysis reaction in higher vertebrates by a serum fraction (fraction P) from the pregnant Salamandra salamandra L]. / Inhibition d'une réaction d'hémolyse immune chez les vertébrés supérieurs par une fraction sérique (fraction P) de femelle gestante chez Salamandra salamandra L.

Serum "fraction P" from Salamandra pregnant female (containing essentially an alpha 2-macroglobulin) possesses non specific cellular immunosuppressive properties [2]. This fraction has been tested in an immune hemolysis reaction: hemolytic Rabbit IgG + guinea-pig complement + Sheep erythrocytes. This fraction, after incubation with guinea-pig complement, inhibits immune lysis.

[In vivo and in vitro study of the effect of pregnant female serum graft rejection in Salamandra salamandra Lin]. / Etude in vivo et in vitro de l'activité du sérum de femelle gestante sur la réaction de rejet de greffe chez Salamandra salamandra Lin.

Serum from pregnant female Salamandra salamandra inhibits the cytotoxic reaction from the mother towards its larvae. Such a serum accelerates the allograft rejection reaction. In vitro studies show that a serum from pregnant female inhibits the cytotoxic reaction of host spleen cells towards epithelial cells of the donor of the graft.

Antagonistic maternal immune reactions (rejection and facilitation) to the embryo in the urodele amphibian Salamandra salamandra lin.

In vitro assays have been employed to demonstrate that pregnant salamanders mount an immune reaction against their embryos. Maternal spleen cells kill up to 85% of dissociated embryonic epidermal cells during a 48 h incubation period. The degree of killing depends upon the ratio of maternal to embryonic cells and on the number of embryos borne by the mother. The cytotoxicity shows considerable specificity for the embryos of a given mother although a weak degree of killing can occur with embryos from other mothers, presumably due to some form of cross-reactivity. The effect is inhibited by the addition of maternal serum to the cultures. The degree of protection is also a function of the number of embryos borne by the mother. Pre-incubation experiments indicate that the maternal serum has a protective action on the embryonic cells which is largely specific for the female's own embryos (and suggested to be antibody in nature) and an inhibitory action on the maternal spleen cells which occurs also with spleen cells of other females (and suggested to be either an immune complex or a nonimmunological substances). An increase in beta protein peaks is seen following electrophoresis of sera from pregnant (and also allografted) salamanders. These findings indicate that the pregnant salamander mounts a double immune reaction against her embryos, an aggressive (rejection) reaction and a protective (facilitation) reaction.

[The maternal protection reaction against a mother's rejection of her own larva in Salamandra salamandra L]. / Etude de la réaction de protection maternelle contre une réaction de rejet de la mère à l'égard de ses larves chez salamandra salamandra L.

In vitro experiments have shown that maternal spleen cells from Salamandra salamandra are cytotoxic to cells from their embryos. This reaction can be inhibited by maternal serum. In this paper, we show that maternal serum protection acts through two effects: by inactivating spleen cells and by protecting embryonic cells. The more numerous the embryos are in a female, the stronger the protection is. The effect of the maternal serum does not appear to be individual specific.

[Demonstration and in vitro study of a complex reaction (rejection and facilitation) of the mother towards the embryo in the urodele amphibian Salamandra salamandra L]. / Mise en évidence et étude in vitro d'une réaction immunitaire complexe (rejet et facilitation) de la mére envers l'embryon chez l'Amphibien Urodèle Salamandra salamandra L

Spleen cells from pregnant (but not from non-pregnant) Salamandra salamandra are cytotoxic in vitro for dissociated epidermal cells from their own embryos. Maternal serum inhibits this cytotoxicity. Analogies and differences are stressed in Salamandra salamandra between allograft rejection mechanisms and immune reactions towards embryos. They may contribute to an explanation of the delayed expulsion of embryos.