AUTHOR=Bonin Jesse L. , Torres Steven R. , Marcinkiewicz Ashley L. , Duhamel Gerald E. , Yang Xiuli , Pal Utpal , DiSpirito Julia M. , Nowak Tristan A. , Lin Yi-Pin , MacNamara Katherine C. 

TITLE=Impact of E. muris infection on B. burgdorferi–induced joint pathology in mice

JOURNAL=Frontiers in Immunology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2024.1430419

DOI=10.3389/fimmu.2024.1430419

ISSN=1664-3224

ABSTRACT=<p>Tick-borne infections are increasing in the United States and around the world. The most common tick-borne disease in the United States is Lyme disease caused by infection with the spirochete <italic>Borrelia burgdorferi</italic> (<italic>Bb</italic>), and pathogenesis varies from subclinical to severe. <italic>Bb</italic> infection is transmitted by <italic>Ixodes</italic> ticks, which can carry multiple other microbial pathogens, including <italic>Ehrlichia</italic> species. To address how the simultaneous inoculation of a distinct pathogen impacted the course of <italic>Bb</italic>-induced disease, we used C57BL/6 (B6) mice which are susceptible to <italic>Bb</italic> infection but develop only mild joint pathology. While infection of B6 mice with <italic>Bb</italic> alone resulted in minimal inflammatory responses, mice co-infected with both <italic>Bb</italic> and the obligate intracellular pathogen <italic>Ehrlichia muris</italic> (<italic>Em</italic>) displayed hematologic changes, inflammatory cytokine production, and emergency myelopoiesis similar to what was observed in mice infected only with <italic>Em</italic>. Moreover, infection of B6 mice with <italic>Bb</italic> alone resulted in no detectable joint inflammation, whereas mice co-infected with both <italic>Em</italic> and <italic>Bb</italic> exhibited significant inflammation of the ankle joint. Our findings support the concept that co-infection with <italic>Ehrlichia</italic> can exacerbate inflammation, resulting in more severe <italic>Bb</italic>-induced disease.</p>