FIG 5.

Immune response against total B. burgdorferi lysate demonstrates the diminished persistence of the bgpmut strain in mice. Proteins of B. burgdorferi lysate resolved by SDS-PAGE were blotted on an Immobilon-P membrane, and strips cut from the blots were then probed with sera recovered from different mice 14 days postinfection. For each strain, strips cut from the same blot were used, except for the mutant, for which strips from two blots run together in the same setup were used. Anti-mouse-IgG-AP secondary antibodies were used for detection of protein bands. Arrows indicate potential recognition of medium components associated with B. burgdorferi by mice sera, because these bands were also detected when probed with uninfected mouse serum. Mean densitometric readings with sera from all mice infected with each dose of infection with the respective strains are provided at the bottom. Sera recovered from WT strain (B31 5A4 and B31 A18)-infected mice produced a strong reaction (3/3 mice); however, the intensity of bands was not significantly different between doses of infection for the two WT strains. An intense reaction by WT strains observed even at doses as low as 100 spirochetes/mouse was significantly higher than in the bgpmut-infected mice with B. burgdorferi proteins (***, P < 0.001 compared to B31 5A4; **, P < 0.01 compared to B31 5A18) and was not significantly different from the reaction in the complemented strain at the same dose of infection. The difference between immunological responses against B31 5A4 and bgpmut strains was most significant at an inoculum of 10³ bacteria/mouse (****, P < 0.0001) and was reduced, albeit remaining significant, at the infection dose of 10⁴ bacteria/mouse (*, P < 0.05). A significant difference between B31 5A18 and bgpmut was also observed at an inoculum of ≥10³ bacteria (***, P < 0.001). The reaction of sera from the complemented-strain-infected mice at doses of ≥10³ spirochetes/mouse was significantly higher than from bgpmut-infected mice at the same inoculum (**, P < 0.01).