A luminescence-based assay for evaluating bactericidal antibody to Borrelia burgdorferi in vaccinated horses’ serum.

This research explores a new luminescence-based serum bactericidal assay (L-SBA) that can accurately identify bactericidal antibodies that can kill the Lyme disease-causing bacteria, Borrelia burgdorferi, in the blood of vaccinated horses. The research shows that there is a correlation between L-SBA and anti-outer surface protein A (one of Borrelia burgdorferi’s proteins) levels in vaccinated horses, suggesting that L-SBA could be effectively used in the future to evaluate the efficiency of vaccines.

Study Objectives and Methods

• The main objective was to create a sensitive and usable L-SBA to identify serum bactericidal activity against Borrelia burgdorferi, which is not possible with existing serological testing.
• The researchers conducted a prospective validation study and method comparison on blood samples obtained from a vaccination trial of 238 horses and from archives of Cornell University’s Animal Health Diagnostic Center.
• The test used an endogenous complement-inactivated serum sample incubated with exogenic complement and a strain of B. burgdorferi modified to produce luminescence in the presence of viable Borrelia.
• The light signal produced after incubation was measured using a luminometer to ascertain the borreliacidal antibody titre in the serum.

Results

• The reaction mixture components, including various sources and concentrations of spirochetes and complement, were tested to find a reliable formula for the L-SBA.
• The researchers determined the half inhibitory concentration of serum samples from the clinical collection.
• The L-SBA titres and levels of anti-outer surface protein A (OspA) antibodies from vaccinated horses were analyzed and showed a correlation, indicating that an increase in L-SBA titres corresponds to an increase in anti-OspA antibody levels in the serum.

Conclusions

• The researchers noted that the immunoreactivity of commercial complement can vary between different batches, and the clinical protection of borreliacidal antibody levels is yet to be determined.
• Overall, the L-SBA presented a sensitive and easy-to-use platform for evaluating bactericidal antibodies to B. burgdorferi. The researchers anticipate the L-SBA could serve as an effective tool to evaluate vaccine efficiency in the future.