Nine out of ten people with lupus are women, a major gender gap long postulated to be linked with immunoregulation by estrogen and androgens. Now, a new line of research suggests that the hormonal predisposition toward lupus may have some of its roots in the gut.
In a mouse model of lupus, feeding male microbiota to females dramatically delays onset of lupus symptoms and mortality, apparently by improving the function of Treg-producing CD103 dendritic cells in the lamina propria of the intestines, according to Michele Kosiewicz, Ph.D., an immunologist at the University of Louisville. Though the research is still in the preliminary stages, it's raising hopes of microbiome-oriented treatment of lupus in the future — and also revealing new ways in which hormones may act on the immune system through the microbes that reside in the digestive system.
"There is definitely something going on that we believe we can tap into," Dr. Kosiewicz said.
Picture Dr. Kosiewicz's research as a series of puzzle pieces, clicking gradually in place. First: Regulatory T cells, well-known to be linked to autoimmune disease. In humans, an x-linked mutation involving the FOXP3 gene dysregulates Treg cells and causes IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, x-linked), marked by widespread autoimmunity and, typically, death in the first two years of life. Mice also show autoimmunity in the absence of CD4-positive FOXP3-positive regulatory T cells, and most autoimmune diseases in mice and humans are associated with defects are in function or in number of these cells.
Dr. Kosiewicz and her colleagues study lupus using the BWF1 mouse model, in which females get the disease early in life and males either don't succumb to it or develop lupus when they are very elderly. In these mice, females have 25 percent to 30 percent fewer Treg cells than males, Kosiewicz said. An investigation of why led to the second piece in the puzzle: The intestine.
Tregs can be generated in either the thymus or in the periphery, e.g., the gut, and an analysis of the markers on the cell surface of the mouse Tregs revealed that the female deficit arose from the intestinal — or peripheral — source.
From there, the trail led to the CD103 dendritic cells that produce Tregs in the intestine. The researchers set out to figure out why these dendritic cells were defective. To do so, they turned to a third puzzle piece: hormones. The researchers knew that if their BWF1 male mice were castrated, they developed lupus rapidly, just like females. Why, they wondered, were androgens so protective?
Castration, they found, dramatically diminished the ability of CD103 dendritic cells to induce regulatory cells, Dr. Kosiewicz said. "That was an androgen link," she said. Puzzle piece three snapped into place.
Next, a fourth puzzle piece presented itself.
"Around the time we were making all these discoveries, we saw a paper in Science by Jayne Danska at the University of Toronto," Dr. Kosiewicz said. Danska and her team were studying a mouse model of Type 1 diabetes that — unlike the human disease — presented primarily in females. They found differences in the microbiota in the guts of male versus female mice, and also found that they could prevent the development of diabetes by transferring microbiota from males to females.
Given the gender gap in lupus and the presence of CD103 cells in the gut, it was logical to see if the microbiome link held up in the BWF1 lupus mice, Dr. Kosiewicz said. The researchers first found that the microbial composition was different in the guts of male and female mice, and that the differences emerged in adulthood, suggesting a hormonal effect.
Next, the researchers fed the female mice fecal samples from male mice. This treatment reduced anti-dsDNA antibody production.. It also dramatically improved kidney symptoms and survival. Typically, Dr. Kosiewicz said, the survival rate of the female lupus mice is only about 10 percent to 20 percent by 36 weeks of life. With the fecal treatment, that survival rate jumped to 80 percent.
"It's a remarkable delay in the disease process," she said.
Dr. Kosiewicz's research suggests that hormones help determine which microbes flourish.
It seems likely, she said, that androgens encourage a microbial milieu crucial to the proper functioning of the CD103 dendritic cells, though androgens might also work directly on dendritic cells and on other tissue that in turn affects those cells. The team is working now to identify the particular microbes that might be involved, though Dr. Kosiewicz expects that there may not be a single culprit. More useful for future treatments, she said, might be another effort she and her colleagues have launched, a search for relevant metabolites created by the microbes, including androgens.
The researchers have already discovered one metabolite, a byproduct of chlorophil breakdown, that has a direct effect on CD103 dendritic cells, Dr. Kosiewicz said, declining to name the substance until peer-reviewed publication and further testing. Desperate patients might be tempted to seek out over-the-counter supplements of the metabolites discovered, she said, but some can have toxic side effects, and they haven't yet been tested in humans. In mice, feeding of the metabolite to female mice resulted in a significant but relatively small delay in disease progress, Kosiewicz said, but the researchers aren't sure why the effect was limited. It might be that the dosing and delivery wasn't effective, she said, or it might be that a combination of metabolites will be necessary for any potential treatment.
Each mouse experiment takes 70 weeks, and each must be repeated multiple times to be sure the results are trustworthy, making for a "character-building" pace, Dr. Kosiewicz said. Chatter about clinical trials for fecal transplants will probably escalate in the near future, she said, though there are many questions about side effects in immunocompromised patients as well as how to match donors to recipients. In the meantime, she said, a balanced, varied diet — while not the most exciting advice — is likely to promote healthy gut flora in anyone.
"We are very excited about our data and the potential to develop therapies, but we just don't know yet," Dr. Kosiewicz said. "My heart goes out to all the patients who are sick. They want a cure now, and the lupus field has been tough."
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