The science behind saliva and blood antibody responses

The more rapid decline in tapeworm-specific salivary antibodies compared with antibodies in blood fits well with a previous study¹ where, tapeworm-specific IgG(T) antibodies were produced at the site of infection and secreted as a local mucosal antibody response. The hypothesis is that these antibodies are secreted through the mucosal epithelial cells by transcytosis with the equine analogue of the neonatal Fc receptor (FcRn), rather than the polymeric Ig receptor.²

In contrast to humoral (blood) antibody responses, mucosal antibody responses (typically, but not exclusively, IgA and IgM) have a short persistence and immunological memory. It can, therefore, be reasonably concluded that the antibodies measured in the saliva test are actually mucosal antibodies against tapeworm antigens. If so, these antibodies are produced in the salivary glands by plasma cells that originated as recirculating (via the lymphatic system) B-blasts triggered in the gut submucosa at the site of infection.³  It remains possible that low levels of humoral antibodies could leak into the saliva by transudation or passage through the gingival crevicular space; however, our study data suggest that this is not a significant factor.

1. Pittaway CE, Lawson AL, Coles GC, Wilson AD. Systemic and mucosal IgE antibody responses of horses to infection with Anoplocephala perfoliata. Vet Parasitol. 2014;199:32-41.
    
2. Roopenian DC, Akilesh S. FcRn: the neonatal Fc receptor comes of age. Nat Rev Immunol. 2007;7 715-725
    
3. McGhee JR, and Fujihashi K. Inside the mucosal immune system. PLoS Biol. 2012;10(9): e1001397