Strong humoral responses cannot effectively target the <i>dbpAB</i> mutant overproducing DbpA or DbpB in chronically infected mice.

<p>Subgroups of four or five BALB/c mice each received one single intradermal/subcutaneous injection of 10<sup>5</sup> spirochetes of the clone Δ<i>dbpAB</i>/<i>dbpAB</i>/1, Δ<i>dbpAB</i>/<i>dbpAB</i>/2, Δ<i>dbpAB</i>/<i>dbpA'</i>/1, Δ<i>dbpAB</i>/<i>dbpA'</i>/2, Δ<i>dbpAB</i>/<i>dbpB'</i>/1 or Δ<i>dbpAB</i>/<i>dbpB'</i>/2, and euthanized 4 months later. DNA samples were prepared from samples with a positive culture and analyzed for spirochetal <i>flaB</i> and murine actin DNA copies by qPCR. The data are expressed as spirochete numbers per 10<sup>6</sup> host cells and presented in three groups by combining the subgroups Δ<i>dbpAB</i>/<i>dbpAB</i>/1 and Δ<i>dbpAB</i>/<i>dbpAB</i>/2, Δ<i>dbpAB</i>/<i>dbpA'</i>/1 and Δ<i>dbpAB</i>/<i>dbpA'</i>/2, and Δ<i>dbpAB</i>/<i>dbpB'</i>/1 and Δ<i>dbpAB</i>/<i>dbpB'</i>/2.</p>