Interferon-γ (IFN-γ) recall responses against foot-and-mouth disease virus (FMDV) in FMD vaccinated cattle are utilized to study T-lymphocyte immunity against this virus. Here, a recall IFN-γ assay based on a commercial ELISA was set up using 308 samples from naïve and vaccinated cattle. The assay was used to study cross-reactive responses between different FMDV vaccine strains. Blood samples from cattle immunized with monovalent vaccines containing A24/Cruzeiro/Brazil/55, A/Argentina/2001 or O1/Campos/Brazil/58 strains were tested using purified-inactivated FMDV from homologous and heterologous strains. A24/Cruzeiro was the most efficient IFN-γ inducer in all vaccinated animals, both when included in the vaccine or as stimulating antigen. We demonstrate that this was mainly due to the structural stability of the whole viral particle. These results show that IFN-γ production relies on the presence of 140S particles that can maintain their integrity along the incubation process in vitro, and throughout the vaccine's shelf-life, when used in vivo.

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Non-cytopathic (ncp) type 2 bovine viral diarrhea virus (BVDV-2) is widely prevalent in Argentina causing high mortality rates in cattle herds. In this study, we characterized an Argentinean ncp BVDV-2 field isolate (98-124) compared to a high-virulence reference strain (NY-93), using in silico analysis, in vitro assays, and in vivo infections of colostrum-deprived calves (CDC) to compare pathogenic characters and virulence. In vitro infection of bovine peripheral blood mononuclear cells (PBMC) with BVDV 98-124 induced necrosis shortly after infection while NY-93 strain increased the apoptotic rate in infected cells. Experimental infection of CDC (n = 4 each) with these strains caused an enteric syndrome. High pyrexia was detected in both groups. Viremia and shedding were more prolonged in the CDC infected with the NY-93 strain. In addition, NY-93 infection elicited a severe lymphopenia that lasted for 14 days, whereas 98-124 strain reduced the leukocyte counts for 5 days. All infected animals had a diminished lymphoproliferation activity in response to a mitogen. Neutralizing and anti-NS3 antibodies were detected 3 weeks after infection in all infected calves. Virulence was associated with a more severe clinical score, prolonged immune-suppression, and a greater window for transmission. Studies of apoptosis/necrosis performed after in vitro PBMC infection also revealed differences between both strains that might be correlated to the in vivo pathogenesis. Our results identified 98-124 as a low-virulence strain.

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