Antibody isotype responses in the serum and respiratory tract to primary and secondary infections with equine influenza virus (H3N8).

Abstract Serum antibody (IgG ab , IgM and IgA) responses to primary and secondary infection with influenza A/equine/Newmarket/79 (H3N8) by nebulised aerosol were compared with local (nasopharyngeal and tracheal) antibody responses in ponies. Circulating IgG ab antibody was of long duration after primary infection, whereas IgM responses were short-lived after both primary and secondary infections. The antigenic stimulation of secondary infection with equine influenza was sufficient to induce elevations of serum IgM and IgA in the presence of high levels of circulating IgG ab . These results support the potential of virus-specific IgM measurement for the detection of recent exposure to virus in horses which have high levels of circulating IgG ab . Unlike serum IgG ab , nasal and tracheal wash antibody of this isotype did not show long duration after primary infection, but local antibody memory was demosntrated by anamnestic response on rechallenge. Nasopharyngeal IgA developed later than IgG ab and IgM, and was more durable.