Spirochetal
infections are an important cause of neurological disease. In previous studies of the pathogenesis of spirochetal brain
infection, mice inoculated with Borrelia turicatae, an agent of
tick-borne relapsing fever in North America, developed mild
meningitis and parenchymal activation/infiltration by
interleukin 10 (IL-10)-producing microglia/macrophages. Here, we investigated the
neuroprotective effects of
IL-10 during spirochetal
infection by comparing the outcomes of B. turicatae
infection in wild-type and IL-10-deficient RAG2-deficient mice. Mice were infected with either serotype 1 (Bt1), which causes more brain
infection but lower
bacteremia, or Bt2, which causes less brain
infection but higher
bacteremia.
Interleukin 10 deficiency resulted in early death from subarachnoid/intraparenchymal
brain hemorrhage in Bt2-infected mice. These mice had marked apoptosis of brain microvascular endothelial cells as assessed by terminal
transferase-mediated DNA nick end-labeling staining. In contrast, Bt1
infection caused milder
subarachnoid hemorrhage. Neuronal apoptosis was observed in mice infected with both serotypes and was prominent in the cerebellum. Neutralization of
tumor necrosis factor prevented death and reduced morbidity and
brain injury in mice infected by both serotypes. We conclude that
IL-10 plays a critical role protecting the cerebral microcirculation from spirochetal injury possibly by inhibition effects of
tumor necrosis factor.