Protection induced by a glycoprotein E-deleted bovine herpesvirus type 1 marker strain used either as an inactivated or live attenuated vaccine in cattle.

BACKGROUND: Bovine herpesvirus type 1 (BoHV-1) is the causative agent of respiratory and genital tract infections; causing a high economic loss in all continents. Use of marker vaccines in IBR eradication programs is widely accepted since it allows for protection of the animals against the disease while adding the possibility of differentiating vaccinated from infected animals.The aim of the present study was the development and evaluation of safety and efficacy of a glycoprotein E-deleted (gE-) BoHV-1 marker vaccine strain (BoHV-1ΔgEßgal) generated by homologous recombination, replacing the viral gE gene with the ß-galactosidase (ßgal) gene. RESULTS: In vitro growth kinetics of the BoHV-1ΔgEßgal virus was similar to BoHV-1 LA. The immune response triggered by the new recombinant strain in cattle was characterized both as live attenuated vaccine (LAV) and as an inactivated vaccine. BoHV-1ΔgEßgal was highly immunogenic in both formulations, inducing specific humoral and cellular immune responses. Antibody titers found in animals vaccinated with the inactivated vaccine based on BoHV-1ΔgEßgal was similar to the titers found for the control vaccine (BoHV-1 LA). In the same way, titers of inactivated vaccine groups were significantly higher than any of the LAV immunized groups, independently of the inoculation route (p < 0.001). Levels of IFN-γ were significantly higher (p < 0.001) in those animals that received the LAV compared to those that received the inactivated vaccine. BoHV-1ΔgEßgal exhibited an evident attenuation when administered as a LAV; no virus was detected in nasal secretions of vaccinated or sentinel animals during the post-vaccination period. BoHV-1ΔgEßgal, when used in either formulation, elicited an efficient immune response that protected animals against challenge with virulent wild-type BoHV-1. Also, the deletion of the gE gene served as an immunological marker to differentiate vaccinated animals from infected animals. All animals vaccinated with the BoHV-1ΔgE ßgal strain were protected against disease after challenge and shed significantly less virus than control calves, regardless of the route and formulation they were inoculated. CONCLUSIONS: Based on its attenuation, immunogenicity and protective effect after challenge, BoHV-1ΔgEßgal virus is an efficient and safe vaccine candidate when used either as inactivated or as live attenuated forms.

The early protective thymus-independent antibody response to foot-and-mouth disease virus is mediated by splenic CD9+ B lymphocytes.

Infection of mice with cytopathic foot-and-mouth disease virus (FMDV) induces a rapid and specific thymus-independent (TI) neutralizing antibody response that promptly clears the virus. Herein, it is shown that FMDV-infected dendritic cells (DCs) directly stimulate splenic innate-like CD9(+) B lymphocytes to rapidly (3 days) produce neutralizing anti-FMDV immunoglobulin M antibodies without T-lymphocyte collaboration. In contrast, neither follicular (CD9(-)) B lymphocytes from the spleen nor B lymphocytes from lymph nodes efficiently respond to stimulation with FMDV-infected DCs. The production of these protective neutralizing antibodies is dependent on DC-derived interleukin-6 (IL-6) and on CD9(+) cell-derived IL-10 secretion. In comparison, DCs loaded with UV-inactivated FMDV are significantly less efficient in directly stimulating B lymphocytes to secrete TI antibodies. A critical role of the spleen in the early production of anti-FMDV antibodies in infected mice was also demonstrated in vivo. Indeed, either splenectomy or functional disruption of the marginal zone of the spleen delays and reduces the magnitude of the TI anti-FMDV antibody response in infected mice. Together, these results indicate that in addition to virus localization, the FMDV-mediated modulation of DC functionality is a key parameter that collaborates in the induction of a rapid and protective TI antibody response against this virus.

Impairment of thymus-dependent responses by murine dendritic cells infected with foot-and-mouth disease virus.

Foot-and-mouth disease virus (FMDV) is a cytopathic virus that experimentally infects mice, inducing a thymus-independent neutralizing Ab response that rapidly clears the virus. In contrast, vaccination with UV-inactivated virus induces a typical thymus-dependent (TD) response. In this study we show that dendritic cells (DCs) are susceptible to infection with FMDV in vitro, although viral replication is abortive. Infected DCs down-regulate the expression of MHC class II and CD40 molecules and up-regulate the expression of CD11b. In addition, infected DCs exhibit morphological and functional changes toward a macrophage-like phenotype. FMDV-infected DCs fail to stimulate T cell proliferation in vitro and to boost an Ab response in vivo. Moreover, infection of DCs in vitro induces the secretion of IFN-gamma and the suppressive cytokine IL-10 in cocultures of DCs and splenocytes. High quantities of these cytokines are also detected in the spleens of FMDV-infected mice, but not in the spleens of vaccinated mice. The peak secretion of IFN-gamma and IL-10 is concurrent with the suppression of Con A-mediated proliferation of T cells obtained from the spleens of infected mice. Furthermore, the secretion of these cytokines correlates with the suppression of the response to OVA, a typical TD Ag. Thus, infection of DCs with FMDV induces suppression of TD responses without affecting the induction of a protective thymus-independent response. Later, T cell responses are restored, setting the stage for the development of a long-lasting protective immunity.