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

Subgroups of four or five BALB/c mice each received one single intradermal/subcutaneous injection of 10⁵ spirochetes of the clone ΔdbpAB/dbpAB/1, ΔdbpAB/dbpAB/2, ΔdbpAB/dbpA'/1, ΔdbpAB/dbpA'/2, ΔdbpAB/dbpB'/1 or ΔdbpAB/dbpB'/2, and euthanized 4 months later. DNA samples were prepared from samples with a positive culture and analyzed for spirochetal flaB and murine actin DNA copies by qPCR. The data are expressed as spirochete numbers per 10⁶ host cells and presented in three groups by combining the subgroups ΔdbpAB/dbpAB/1 and ΔdbpAB/dbpAB/2, ΔdbpAB/dbpA'/1 and ΔdbpAB/dbpA'/2, and ΔdbpAB/dbpB'/1 and ΔdbpAB/dbpB'/2.