Isotype profiles induced in Balb/c mice during foot and mouth disease (FMD) virus infection or immunization with different FMD vaccine formulations.

The IgG isotype response in Balb/c mice infected with FMDV or immunized with different vaccine formulations using inactivated virus particles as antigen was analyzed at various times post-inoculation. For this purpose an ELISA based on polyclonal antibodies for detection and quantification of mouse IgG isotypes with FMD virus (FMDV) specificity was developed. Three immunomodulators, which have been shown to be very effective in inducing strong and long-lasting antibody responses (Bahnemann, Arch. Virol. 1975, 47, 47-56; Polatnik and Bachrach, Appl. Microbiol. 1964, 12, 368-376), were employed to formulate different vaccines using aqueous and oil vehicles: a water-soluble fraction of the cell wall of Mycobacterium sp., a purified extract of lipopolysacharide from Brucella ovis and a synthetic lipoamide, Avridine. Infected animals between 14 and 60 days post-inoculation (d.p.i.) showed responses dominated by IgG2b, followed by IgG1, IgG2a and IgG3, respectively. The IgG3 isotype was the first, together with IgG1, to be elicited during the first 7 days after infection, whereas no IgG3 activity was detected in vaccinated animals at any time. With formulations including immunomodulators, persisting high levels of IgG2b (similar to those of infected animals) were detected until 180 d.p.i., while with conventional vaccines IgG2b responses were detected up to 60 d.p.i. Animals vaccinated with formulations including these immunomodulators presented an augmented resistance to viral challenge at 210 d.p.i. in relation with those immunized with conventional vaccines. The possible relationship of these differences in the isotype response and protection is discussed.