Influence of outer surface protein A antibody on Borrelia burgdorferi within feeding ticks

Borrelia burgdorferi, the spirochetal agent of Lyme disease, is transmitted by Ixodes ticks, When an infected nymphal tick feeds on a host, the bacter ia increase in number within the tick, after which they invade the ticks sa livary glands and infect the host. Antibodies directed against outer surfac e protein A (OspA) of B. burgdorferi kill spirochetes within feeding ticks and block transmission to the host. In the studies presented here, passive antibody transfer experiments were carried out to determine the OspA antibo dy titer required to block transmission to the rodent host. OspA antibody l evels were determined by using a competitive enzyme-linked immunosorbent as say that measured antibody binding to a protective epitope defined by monoc lonal antibody C3.78, The C3.78 OspA antibody titer (>213 mu g/ml) required to eradicate spirochetes from feeding ticks was considerably higher than t he titer (>6 mu g/ml) required to block transmission to the host, Although spirochetes were not eradicated from ticks at laffer antibody levels, the a ntibodies reduced the number of spirochetes within the feeding ticks and in terfered with the ability of spirochetes to induce ospC and invade the sali vary glands of the vector. OspA antibodies may directly interfere with the ability of B. burgdorferi to invade the salivary glands of the vector; alte rnately, OspA antibodies may lower the density of spirochetes within feedin g ticks below a critical threshold required for initiating events linked to transmission.