Sunlight exposure linked to autoimmune diseases, kidney damage

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In a new study, researchers found how skin exposure to ultraviolet (UV) light can worsen clinical symptoms in autoimmune diseases such as lupus.

The research was conducted by a team at Dartmouth and elsewhere.

Lupus, an autoimmune disease that can cause inflammation of the joints, skin, kidneys, blood cells, brain, heart and lungs, is caused when the immune system attacks its own tissue.

Previous research has established that in up to 80 percent of lupus patients, sunlight exposure can trigger both local skin inflammation and systemic flares, including kidney disease.

But little has been understood about the underlying mechanisms that drive this process.

To define how UV light triggers kidney inflammation, the team examine the role of neutrophils—a type of white blood cell abundantly found in the body that acts as a first responder to any kind of inflammation and has been linked to skin and kidney tissue injury in lupus patients.

In the study, they looked for markers of inflammation and injury in the skin, the blood, and the kidney at different time points following UV light exposure in mice.

They were able to find that neutrophils not only infiltrated the UV light-exposed skin but also dispersed throughout the circulatory system and migrated to the kidney.

They found that a single exposure of skin to UV light stimulates inflammatory and injury processes in the kidney, including transient proteinuria, even in normal, healthy mice.

To be clear, the team says normal, healthy mice don’t get the clinical type of kidney disease that is in lupus patients.

They get what we call subclinical injury, meaning there is an inflammatory and injury process happening in the kidney that is not visible by pathology or looking at the tissue itself. The mice recover and are fine afterward.

However, 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.

Importantly, the inflammatory and injury markers they detected in the mouse kidneys following UV light exposure were very similar to the renal injury markers that are linked to more severe kidney damage in lupus patients.

In addition, the exposure to UV light also triggered an immune response that is often expressed in most lupus patients—the type 1 interferon response—in both the skin and kidney.

One author of the study is Sladjana Skopelja-Gardner.

The study is published in PNAS.

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