Desenvolvimento e imunogenicidade de uma vacina de aplicação intravaginal contra o alphaherpesvírus bovino tipo 5 (BoHV-5) associada a subunidade B recombinante da enterotoxina termolábil de Escherichia coli (rLTB)

Abstract

The mucosal immune system represents the initial barrier against several pathogens that use these surfaces as a gateway into the body, as is the case with bovine alphaherpesviruses (BoHV). These viruses use mucous membranes, mainly nasal and genital, as the initial point of replication, followed by local dissemination, viremia and neuronal dissemination. Due to the great importance of mucous pathways in the transmission of BoHV, it is evident the interest in the development of vaccines that provide mucosal immunity against these viruses. In the present study, 63 Braford bovine females were divided into seven groups of nine animals and were inoculated intravaginally with inactivated BoHV-5, associated with the recombinant B subunit of the E. coli thermolabile enterotoxin (rLTB) as follows: G1 (2-hydroxyethylcellulose + BoHV-5 + rLTB), G2 (2-hydroxyethylcellulose + BoHV-5), G3 (Poloxamer 407 + BoHV- 5 + rLTB), G4 (Poloxamer 407 + BoHV-5), G5 (BoHV-5 + rLTB), G6 (Negative control) and G7 (Positive control). The local and systemic humoral response induced in the inoculated animals was measured using the indirect ELISA test (IgA and IgG) and serum neutralization, and the cellular response by direct quantitative ELISA (IL-2 and IFN-Gamma). As a result, in the vaginal mucosa, the intramuscular group, G5 provided the highest levels of IgG, the experimental groups with polymers (G1 and G3) were statistically superior (p <0.01), compared to the positive control group (G7), as well as, regarding the IgA levels observed in the vaginal mucosa at 30, 60 and 90 days after the first inoculation. Groups G1 and G3 also provided higher titers of neutralizing antibodies (log2) in relation to the other treatments (p <0.01) 90 days after inoculation, demonstrating the efficiency of the tested polymers as an antigen delivery system. In the nasal mucosa, there was an increase in the levels of IgA and IgG with the use of vaccines in groups G1 and G3, in relation to the positive control, G7 (p <0.05) at 60 and 90 days after the first inoculation, which emphasizes the strong relationship between mucosal systems. The inoculation of experimental vaccines also resulted in an increase in the levels of IgA and IgG in the serum of the animals, measured by indirect ELISA, in addition to presenting neutralizing antibody titers at 60 and 90 days, detected through serum neutralization. The highest titers of neutralizing antibodies were provided by the G5 group (without polymers and intramuscular). The intravaginal vaccine has been shown to increase the levels of IgA and IgG and interleukins in the serum and in the nasal and vaginal mucosa of immunized cattle. These data prove the capacity of the vaccine for intravaginal application in cattle to stimulate a local and systemic immune response, in addition to corroborating the immunostimulating activityin mucous membranes of rLTB. Thus, this route of administration of vaccines becomes a promising alternative, especially when the objective is to generate local protection against pathogens that use mucous surfaces as a gateway to the organism.