REACTIVITY WITH A SPECIFIC EPITOPE OF OUTER SURFACE PROTEIN-A PREDICTS PROTECTION FROM INFECTION WITH THE LYME-DISEASE SPIROCHETE, BORRELIA-BURGDORFERI

The response to recombinant vaccines for Lyme disease was studied to d etermine serum antibody levels effective in protecting against tick-tr ansmitted infection. Data presented here demonstrate a significant cor relation between antibody to an epitope on outer surface protein A (Os pA) and protection against infection with Borrelia burgdorferi in cani nes and mice, A competitive enzyme-linked immunosorbent assay was deve loped to measure antibody to a site on OspA, defined by monoclonal ant ibody LA-2, Comparison of LA-2 titers against infection of canines and mice following vaccination and challenge established a predicted valu e for LA-2 titers, The statistical relationship between serum antibody levels and protection was calculated by logistic regression analysis. The statistical model predicted that an LA-2 titer of 0.32 mu g equiv alents (eq) per mi correlated to an 80% predicted probability of prote ction for both mice and dogs. This value was used to classify mice and dogs as to their protected status at the time of tick exposure, The L A-2 cutoff titer (0.32 mu g eq/ml) correctly classified all dogs (n = 13) and mice (n = 44) that failed to become infected. By contrast, 20 of 22 dogs and 28 of 31 mice with titers of less than 0.32 mu g eq/ml became infected. On the basis of these results, we conclude that an LA -2 titer is a reliable indicator of immune status for estimating immun e protection following use of OspA-based vaccines for B. burgdorferi s ensu stricto.