Lyme bacteria find unlikely safe haven

UC DAVIS (US) — By hiding out in the lymph nodes, the bacteria that cause Lyme disease are able to both provoke and elude immune responses in the animals they infect.

Published in the journal PLoS Biology, the findings involving mice may explain why some people experience repeated infections of Lyme disease.

“Our findings suggest for the first time that Borrelia burgdorferi, the bacteria that cause Lyme disease in people, dogs, and wildlife, have developed a novel strategy for subverting the immune response of the animals they infect,” says Nicole Baumgarth, associate professor of pathology, microbiology, and immunology at the University of California, Davis.

“At first it seems counterintuitive that an infectious organism would choose to migrate to the lymph nodes where it would automatically trigger an immune response in the host animal. But B. burgdorferi have apparently struck an intricate balance.”

Lyme disease, the most important tick-borne disease in the United States is caused by Borrelia burgdorferi, corkscrew-shaped bacteria also known as spirochetes. The disease is transmitted to humans and animals through bites from infected deer ticks.

It occurs mainly in the Northeastern and Great Lakes states, and is present to a lesser extent in Northern California. However, the western black-legged tick, the main carrier of Lyme disease in the western United States, has been found in 56 of California’s 58 counties, according to the California Department of Public Health.

Symptoms of Lyme disease may include fever, headache, fatigue, and a skin rash. It can be treated with about four weeks of antibiotics, most successful during the early stages of infection. Untreated, it can spread to the joints, heart, and nervous system.

Swollen lymph nodes, or lymphadenopathy, is one of the hallmarks of Lyme disease, although it has been unclear why this occurs or how it affects the course of the disease.

Researchers discovered that when mice were infected with B. burgdorferi, the live spirochetes accumulated in the animals’ lymph nodes, that then responded with a strong, rapid accumulation of B cells—white blood cells that produce antibodies to fight infections.

The presence of B. burgdorferi also caused the destruction of the distinct architecture of the lymph node that usually helps it to function normally.

While B cells accumulated in large numbers and made some specific antibodies against B. burgdorferi, they did not form “germinal centers,” structures that are needed for the generation of highly functional and long-lived antibody responses.

“Overall, these findings suggest that B. burgdorferi hinder the immune system from generating a response that is fully functional and that can persist and protect after repeat infections,” Baumgarth says.

“Thus, the study might explain why people living in endemic areas can be repeatedly infected with these disease-causing spirochetes.”

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