Background IgG is a major antibody isotype in serum and is transferred to saliva in humans and ruminants. Vaccination strategies against rumen-dwelling organisms such as methanogens aim to induce high levels of antibody in saliva, yet saliva is difficult to collect in sufficient volumes for routine analysis. This study evaluated whether serum could serve as a surrogate for saliva in assessing antigen-specific IgG responses in sheep. Methods Paired serum and saliva samples were collected from animals vaccinated with antigens of varying complexity: a single recombinant protein (SP1), two protein cocktails, and a mixture of five methanogen strains (Mix5). Forty-one paired serum and saliva samples were analyzed. Antigen-specific IgG, IgG1, and IgG2 titers in serum and saliva were compared using ELISA and western blotting. Antibody avidity was determined using a chaotropic agent in the ELISA. Results Serum and saliva showed strong overall correlation for antibody titers, and the specificities of antibody-antigen interaction were very similar for serum and salivary antigen-specific IgG, IgG1 and IgG2 antibodies. For antibody avidity, the data supported a broad positive relationship between serum and salivary IgG; however, additional methodological refinement and validation are required before this relationship can be confidently extrapolated across antigen types. Conclusions Collectively, these results demonstrate that serum provides a robust and practical surrogate for assessing key immunological properties of antigen-specific IgG in sheep saliva.
Yeung et al. (Wed,) studied this question.