A study reveals that skin exposure to ultraviolet (UV) light can worsen clinical symptoms in autoimmune diseases such as lupus, an unexpected insight.
Prior research has determined that sunlight exposure can trigger local skin inflammation, systemic flares, and kidney disease in up to 80 percent of lupus patients. The underlying mechanisms that drive this process are yet to be understood.
Researchers looked for inflammation and injury in the skin, blood, and kidney at different time points following UV light exposure in mice. They were able to demonstrate that neutrophils (a type of white blood cell that responds immediately to any type of inflammation) not only sneak into the UV light-exposed skin but were also found throughout the circulatory system and moving toward the kidney.
"Interestingly, one subset of these neutrophils, the ones that we think are more damaging, first went to the skin that was exposed to the UV light and then turned around and went to the kidney," says Sladjana Skopelja-Gardner. "We normally think of neutrophils as short-lived cells that sort of zoom to where the inflammation is and then die off there." Findings also showed that even a single exposure of skin to UV light could cause inflammation and injury in the kidney, including transient proteinuria, of even healthy mice.
Skopelja-Gardner continues, "To be clear, normal, healthy mice don't get the clinical type of kidney disease that you see in lupus patients." She explains that they get subclinical injuries, i.e., not visible by pathology or looking at the tissue itself.
She adds, "This subclinical injury may lead to pathologic consequences in the vulnerable setting of pre-existing inflammation in lupus patients, and lead to kidney disease flare after exposure to sunlight."
The inflammatory and injury markers detected in the mouse kidneys were similar to those found in renal injuries and are associated with more severe kidney damage in lupus patients. Exposure to UV light also led to an immune response - the type 1 interferon response - in both the skin and kidney, often found in lupus patients.
In conclusion, the study demonstrates that exposure of skin to UV light can be the source of inflammatory pathways relevant to lupus and that neutrophils play a vital role as a pathogenic mediator in this process.