Gut Check

“It is changing the metabolism of the cells, which can alter inflammatory responses,” Castillo says. “During intestinal inflammation – states of chronic illness such as ulcerative colitis and Crohn’s disease, both forms of IBD – these macrophages become more inflammatory and they’re more abundant in the gut.”

The multitude of cell types in the gut are all interconnected, he says. “If you perturb any one of them you can perturb all of them. If we’re constantly ingesting microplastics you can see how this can start to affect not only the gut but the rest of the immune system.”

Microplastics, which are also found floating in the air, are unlike anything the immune system has encountered over millions of years of evolution, and the macrophages have difficulty digesting them, Castillo says.

In the course of the study, the scientists saw that the particles remained within the macrophages. “What we have observed is they are no longer 10-micron size, he says. “They may be breaking up, but they were not degraded within our (study) time frame.”

Matthew Campen, PhD, a professor in the UNM Department of Pharmaceutical Sciences who was a co-author on the paper, adds, “Our immune systems didn’t evolve to deal with this, so there’s a possibility this is reprogramming our immune system to make us more vulnerable to autoimmune conditions,” he said.

The sheer volume of plastics that are present in the environment is concerning. Campen recounts that his children found microplastics in a water sample taken for a school science project near the headwaters of the Rio Grande in Colorado.

“It’s clearly ubiquitous,” he says. While people might not be keeling not over from plastics exposure, the incidence of autoimmune disease has skyrocketed. “We’re kind of looking at the tip of the iceberg with regard to plastics waste that we’ve generated.”

An additional concern, Campen adds, is that dangerous microbes or toxic chemicals might hitch a ride on microplastic particles and find their way into the body. That is true both in the gut and in the lungs, where macrophages serve a similar protective function.

Worse still, not all plastics are alike. Exposure to the ultraviolet radiation in sunlight degrades the surface of plastic particles, leading to the release of toxic chemical compounds, Campen says. While chemists have developed biodegradable plastics that break down in the environment, that might be problematic in itself.

“Eliseo started studying biodegradable plastics,” Campen says. “His early data suggested they might be even more toxic. We’re trying to push for companies to consider what degradation products will be most viable, not just for humans but for whole ecosystems.”