Characterizing the impact of intracutaneous dissemination on host responses during Borrelia burgdorferi infection.

UNLABELLED: To investigate the unique dissemination phenotype of a mutant in OppA2 of Borrelia burgdorferi (Bb), one of the five encoded peptide binding proteins of the peptide transport system. Our previous study showed that loss of OppA2 abrogates hematogenous dissemination, restricting the bacteria to intracutaneous dissemination routes. Herein, we further define this unique dissemination phenotype and seek to understand the resultant dampening of the host serological response during infection.

METHODS

We utilized longitudinal infection models to evaluate dissemination, cytometric and histopathologic analysis, spatial immune profiling, ELISA, and host immune response transcriptomics.

RESULTS

Dissemination studies demonstrate that at 4 weeks post-inoculation (wpi), in addition to skin colonization, oppA2tn can be found in lymph nodes. By 8 wpi the oppA2tn mutant fully disseminates throughout the skin and by 20 wpi sporadic dissemination to distal organs. While immune cell populations do not show significant changes between wild-type and mutant infections, we see dramatic effects related to antibody responses, as well as host transcriptional responses during early infection. We further evaluated the roles of MyD88 signaling and the adaptive immune system (using MyD88 and SCID knockout mice, respectively) in limiting intracutaneous dissemination. We found that both immune components appear to control spirochete dissemination in the skin, as both mouse strains displayed faster skin colonization as well as distal site colonization.

CONCLUSIONS

Colonization of lymph nodes at 4 week post-inoculation by the oppA2tn mutant strongly implies that eventual organ colonization arises from lymphatic dissemination, a phenomenon that has been difficult to study when paired with hematogenous dissemination. Additionally, the dampening of immune responses show that sequestration of the bacteria to skin during early infections results in integral changes in how the host both detects and responds to the spirochete. Together, these data shed light on the role hematogenous dissemination plays in generating a robust anti-Bb immunological response and suggests that distal sites of colonization are integral for eliciting typical serological responses and inflammatory profiles observed in wild type Bb-murine infections.