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SALT LAKE CITY — An international team of researchers say a protein found in human sweat may help protect people from Lyme disease, a tick-borne illness that affects nearly a half-million people every year in the U.S. However, a variation of that protein may actually increase the risk of developing Lyme disease.
The study is published in Nature Communications.
The researchers, from MIT and the University of Helsinki, said they hope the finding will lead to the development of skin creams or other products that ward off tick bites and prevent the disease, which is described by the Centers for Disease Control and Prevention as the "most common vector-borne disease" in America.
While studying the disease to see if they could figure out whether some people are more susceptible to Lyme disease than others, the researchers said they found the protein in sweat that appears to be protective. About one-third of the population carries a variant of that sweat protein that is instead associated with getting Lyme disease.
In an MIT news release, the researchers said they don't know how the protein reduces bacterial growth. That's subject to further study. But study senior author Michal Caspi Tal, a principal research scientist in MIT's Biological Engineering Department, said he and his colleagues "think there are real implications here for a preventative and possibly a therapeutic based on this protein."
Spread — and control — of Lyme disease
The bacterium Borrelia burgdorferi is usually the cause of Lyme disease, which is spread primarily by blacklegged ticks carried by mice, deer and other animals, per the researchers. While antibiotics typically clear the infection, others can have a hard time shaking it, leading to months and sometimes years of symptoms.
Typical symptomatic Lyme disease can include fever, headache, fatigue and a skin rash called erythema migrans, the CDC reports. "If left untreated, infection can spread to joints, the heart and the nervous system." One of the big challenges is the ticks are so small that people sometimes don't know they've been bitten and removing the tick quickly — and completely — is key to reducing the risk of being infected.
"Most patients receive doxycycline, an antibiotic that usually clears up the infection," the news release said. "In some patients, however, symptoms such as fatigue, memory problems, sleep disruption and body aches can persist for months or years."
About the research
The other lead author, Hanna Ollila, is a senior researcher at the Institute for Molecular Medicine at the University of Helsinki. She's also a researcher at the Broad Institute of MIT and Harvard. She and Tal began the study when they were both postdoctoral students at Stanford University several years ago. They were initially looking for genetic markers that might signal someone is susceptible to Lyme disease.
"To that end, they decided to run a genome-wide association study on a Finnish dataset that contains genome sequences for 410,000 people, along with detailed information on their medical histories," they said in the release.
They got three hits, the last one a surprise that had not been previously linked to Lyme disease. It was a secretoglobin made in the sweat glands. Secretoglobins are a group of proteins in tissues linking lungs and other organs that are part of the body's immune response to an infection. The one they found in the study, designated SCGB1D2, is one of 11 known secretoglobins that humans produce.
In the lab, the researchers exposed both normal and mutated versions of the secretoglobin to the bacterium. The normal protein "significantly inhibited" growth of B. burgdorferi. But it took twice as much of the mutated version to slow bacterial growth.
Tal said the mice stayed healthy during more than a month's follow-up when they had the original version of the sweat protein. "This wasn't a delay, this was a full stop," he said. "That was really exciting."
The paper published in Nature Communications included a confirmatory study, which replicated the results, by a team in Estonia that used data from the Estonian Biobank on 210,000 people, 18,000 of whom had Lyme disease.
Next, the MIT and Helsinki researchers plan to see if putting the protein on mouse skin stops them from being infected. The mice don't produce that secretoglobin naturally. They hope to look as well at whether the protein can help people with infections that are antibiotic-resistant.
"The researchers note that people who have the protective version of (the secretoglobin) can still develop Lyme disease, and they should not assume that they won't. One factor that may play a role is whether the person happens to be sweating when they're bitten by a tick carrying B. burgdorferi," per the release.
