Fig. 5.

BBA57 alters the host antimicrobial response. (A) Assessment of host antibacterial inflammatory response at the dermal injection site. Equal numbers of wild-type B. burgdorferi (WT) or bba57− mutant (bba57−) (10⁵ cells per animal) were injected into the skin. Five days following inoculum, the injection sites were retrieved and processed for a PCR array for simultaneous analysis of expression of 84 host antibacterial response genes. The table summarizes the fold change of gene expression of bba57− mutant compared with WT. Genes up-regulated during mutant infection are represented in red. Blue squares show the most dramatically induced genes, bactericidal/permeability-increasing protein (BPI), and an IFN gene (Ifna9) explored in this study. (B) Up-regulation of BPI during syringe-inoculated infection with bba57 mutants. Equal numbers of WT (white bars) or bba57− (black bars) isolates (10⁵ cells per animal) were injected into mouse skin. Injection sites were retrieved following 5 d of inoculum and analyzed for BPI expression by RT-qPCR. (C) Induction of BPI during tick-borne infection with bba57 mutants. Naive nymphal ticks or nymphs infected with WT (gray bars) or bba57− mutants (black bars) were allowed to parasitize naive mice. After 5 d of feeding, the bite site was retrieved and BPI expression was analyzed by RT-qPCR. (D) Reduction of bba57 mutant-induced BPI expression following depletion of neutrophils. Mice were treated for cell depletion as shown in Fig. 3E. The expression of BPI was measured at the injection site by RT-qPCR after 5 d of infection. (E) BPI induction by neutrophils following exposure with spirochetes in culture. Primary neutrophils were isolated from mice and then immediately incubated in vitro with only medium (white bar), WT B. burgdorferi (gray bar), or bba57− mutants (black bar). Following spirochete exposure, neutrophils were collected, and BPI expression was measured by RT-qPCR. (F) Up-regulation of BPI during infection with an isogenic mutant lacking a key BBA57-modulated gene, ospC. Equal numbers (10⁵ cells) of the WT B. burgdorferi (white bar) or ospC mutants (black bar) were injected into mouse skin. Injection sites at the dermis were retrieved after 5 d of inculum and processed for BPI expression by RT-qPCR. Bars represent the mean ± SEM of at least triplicates. Data in A–F are representative of at least eight mice and two independent experiments. *P < 0.05; ***P < 0.001.