Abstract
Methane is produced in the rumen of ruminant livestock by methanogens and is a major contributor to agricultural greenhouse gases. Vaccination against ruminal methanogens could reduce methane emissions by inducing antibodies in saliva which enter the rumen and impair ability of methanogens to produce methane. Presently, it is not known if vaccination can induce sufficient amounts of antibody in the saliva to target methanogen populations in the rumen and little is known about how long antibody in the rumen remains active. In the current study, sheep were vaccinated twice at a 3-week interval with a model methanogen antigen, recombinant glycosyl transferase protein (rGT2) formulated with one of four adjuvants: saponin, Montanide ISA61, a chitosan thermogel, or a lipid nanoparticle/cationic liposome adjuvant (n = 6/formulation). A control group of sheep (n = 6) was not vaccinated. The highest antigen-specific IgA and IgG responses in both saliva and serum were observed with Montanide ISA61, which promoted levels of salivary antibodies that were five-fold higher than the second most potent adjuvant, saponin. A rGT2-specific IgG standard was used to determine the level of rGT2-specific IgG in serum and saliva. Vaccination with GT2/Montanide ISA61 produced a peak antibody concentration of 7 × 1016 molecules of antigen-specific IgG per litre of saliva, and it was estimated that in the rumen there would be more than 104 molecules of antigen-specific IgG for each methanogen cell. Both IgG and IgA in saliva were shown to be relatively stable in the rumen. Salivary antibody exposed for 1–2 hours to an in vitro simulated rumen environment retained approximately 50% of antigen-binding activity. Collectively, the results from measuring antibody levels and stablility suggest a vaccination-based mitigation strategy for livestock generated methane is in theory feasible.
Highlights
Vaccination against rumen methanogens has the potential to reduce methane emissions from livestock, which is a major contributor to agricultural greenhouse gases [1,2,3]
When the saliva was added to phosphate buffered saline (PBS), the levels of total and Recombinant GT2 (rGT2)-specific IgA and IgG remained at similar levels for up to 4 hours compared to time 0
The level of total IgG decreased by approximately 50% between 0 and 4 hours (P < 0.001) in the presence of inhibitor whereas the levels of rGT2-specific IgG remained constant
Summary
Vaccination against rumen methanogens has the potential to reduce methane emissions from livestock, which is a major contributor to agricultural greenhouse gases [1,2,3]. The concept is to induce salivary anti-methanogen antibodies which are delivered to the rumen and reduce the activity of methane-producing methanogens. In addition to selecting optimal antigens, an effective anti-methanogen vaccine will need to induce sufficiently high levels of salivary antibodies to bind to specific targets on the rumen methanogens [11]. The first aim of the current study were to determine the levels of the major class (IgG and IgA) of immunoglobulin (Ig) in saliva and the rumen of sheep and determine how long antibodies can retain their activity in the rumen. An understanding of salivary antibody concentration will provide theroretical estimation into whether the current vaccination strategy produce enough antibody in the rumen to have an impact on methanogen activity
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