Breaking into a cold sweat over a tick bite may have its benefits.
A protein found in human sweat could offer some protection against Borrelia burgdorferi, a tick-transmitted bacterium that causes Lyme disease, researchers report March 19 in Nature Communications. In lab dishes and mice, the protein curbed bacterial growth. But some people have a mutated version of the protein that doesn’t work as well, perhaps putting them at higher risk of becoming infected.
“When we talk about risk factors for [contracting] Lyme, we generally talk about camping, golfing, maybe gardening,” says MIT immunologist Michal Tal. But sweaty activities like trail running aren’t typically on the list. “It’s never even been a question of whether or not it mattered if you were sweating, and if you had any protection in your sweat.”
Tal and colleagues aimed to find genes that may make some people more susceptible to Lyme disease. The team analyzed genetic data from about 620,000 people who’d been seen at hospitals or primary care clinics in Finland and Estonia. More than 25,000 of those individuals had been diagnosed with Lyme disease.
The analysis uncovered three candidate genes. Two genes provide the instructions to make immune proteins that help the body identify foreign invaders. The third gene codes for SCGB1D2, “a totally unexpected protein that … we didn’t really know anything about,” says geneticist Hanna Ollila of the University of Helsinki. The team eventually figured out that the protein is made in sweat glands and may show up on the skin — the first line of defense against hungry ticks.
In lab dishes, the protein stopped B. burgdorferi from growing. What’s more, mice injected with the protein plus the bacteria didn’t become infected.
However, 40 percent of people in the study carried a mutated version of the protein. In experiments with that variant, twice as much protein was required to curb bacterial growth in lab dishes. And mice injected with the variant alongside the bacteria developed infections.
The results, the researchers say, suggest that the normal version of SCGB1D2 could someday be leveraged as a treatment for Lyme disease, the most common tickborne infection in the United States and Europe (SN: 6/23/19). The protein might also be used as a preventative to stop B. burgdorferi from taking hold. But that would take a bit of engineering. “There’s still a lot of work that remains to be done for us to see just how much potential it has,” Tal says.
The finding raises questions about how the protein might interact with bacteria once a tick digs in for a bite, says medical entomologist Adela Oliva Chávez of the University of Wisconsin–Madison. Tal’s team exposed mice to the bacteria via needle injections, bypassing any tactics the tick might have to make SCGB1D2 less effective (SN: 12/10/20).
Though there are still many unknowns, “I’m excited, with caution,” Oliva Chávez says.
