Qualitative aspects of the immune responses related to protection against FMDV challenge in cattle.

DI GIACOMO, S.; BARRIONUEVO, F.; BUCAFUSCO, D.; MIRAGLIA, M. C.; SCHAMMAS, J.; AYUDE, A.; CAPOZZO, A.; PÉREZ FILGUEIRA, M.

Borgo Egnazia

Congreso; Increasing Global Security in the Suply of Effective FMD Vaccines. XVI Open Session of the Standing Technical and Research Committees of the EuFMD; 2018

European Commission for the Control of Foot-and-Mouth Disease

We have shown that multivalent vaccines, as well as revaccination protocols, could confer complete protection in a well-established vaccine-matching model for cattle using the A24/Cruzeiro and A/Arg/2001 FMDV strains. Experimental groups did not show significant differences among them for a wide range of immunological parameters; however, differences were found between protected and unprotected animals, mainly in the isotype and avidity profiles of the immune sera. In this report, we described some qualitative aspects of the humoral responses found in protected bovines.Materials and MethodsSerum samples from each vaccination protocol [n=5 each: single dose monovalent 10 μg (1)or 40 μg of A24/Cruzeiro (2); trivalent A24/Cruzeiro-O1/Campos-C3/Indaial (3), or two doses of the 10ug of A24/Cruzeiro vaccine (4)] were assayed using a set of newly developed serological tests. These new ELISA-based protocols were used to quantify avidity according to the isotype of the antibodies against A24/Cruzeiro and A/Arg/2001 FMDV strains as well as theamount of A/Arg/2001-specific antibodies generated by the other three heterologous strains.ResultsProtected animals showed significantly lower IgG1/IgG2 ratios than non-protected ones. Protected cattle also presented higher mean avidity indexes (AI) for antibodies against the A/Arg/2001 but also against the A/24 and O1/Campos strains. Such significant differences were also observed when analyzing IgG1 and IgG2 isotypes separately. Strain-specific analyses also shown that both the C3/Indaial- and O1/Campos-specific antibodies showed cross-reactivityagainst the A/Arg/2001 strain in a similar manner.DiscussionOur results would indicate the existence of a higher proportion of cross-reactive IgG2 antibodies,compared to the IgG1 isotype, in the protected individuals. However, higher mean AI against A/Arg/2001 strain found in protected cattle, was not restricted to a specific IgG subclass and it was also detected for other strains (A24/Cruzeiro and O1/Campos). The O1/Campos and C3/Indaial vaccine antigens present in the trivalent formulation effectively generated A/Arg/2001 cross-reactive antibodies observing a similar proportion.