From the Journals

New evidence supports immune system involvement in hidradenitis suppurativa



Immune dysregulation is a substantial feature of hidradenitis suppurativa in African American patients, according to data from 16 adults.

The etiology of hidradenitis suppurativa (HS) remains unknown, but neutrophils are prominent in affected areas of skin, wrote Angel S. Byrd, MD, PhD, of Johns Hopkins University, Baltimore, and colleagues.

“Among the several functions of neutrophils, these cells have the ability to form neutrophil extracellular traps (NETs) after exposure to certain microbes or sterile stimuli,” the researchers noted. These NETs are weblike structures that have been shown to activate several types of immune responses and promote inflammation.

In a study published in Science Translational Medicine, the researchers analyzed biospecimens from African American HS patients. They determined that NET structures were present in the lesional skin of HS patients, but not in control skin. Additionally, serum from HS patients did not properly degrade healthy control NETs in an in vitro examination.

A significant correlation (P less than .0001) occurred between the amount of NETs released in hidradenitis suppurativa lesions and hidradenitis suppurativa severity.

“Together, these results indicate that NET formation is enhanced in HS, both systemically and in lesional skin, in association with disease severity and that NET degradation mechanisms may be impaired in this disease,” the researchers wrote.

The researchers also found that total immunoglobulin G was significantly increased in the sera of HS patients, compared with that of healthy volunteers (P = .0011), and that enzymes involved in skin citrullination were elevated in the skin of HS patients, compared with controls’ skin.

Previous studies have shown that NETs can promote type I interferon (IFN) signatures in the blood of patients with autoimmune and chronic inflammatory conditions, and in this study, several type I IFN–regulated genes had increased expression in HS skin, including IFI44L, MX1, CXCL10, RSAD2, and IFI27.

The study findings were limited by the small sample size and homogenous population, the researchers noted. Future research should include “the role that neutrophil/type I IFN dysregulation plays in the clinical manifestations of the disease, and how these abnormalities in immune responses regulate other innate and adaptive immune cell types in HS,” which could affect the development of new treatments, they wrote.

The study was supported in part by the National Institutes of Health, the Johns Hopkins School of Medicine Physician Scientist Training Program, and the Danby Hidradenitis Suppurativa Foundation. Dr. Byrd disclosed participating in the Johns Hopkins Ethnic Skin Fellowship, which was supported in part by Valeant. Dr. Byrd also disclosed serving as a former investigator for Eli Lilly.

SOURCE: Byrd AS et al. Sci Transl Med. 2019 Sep 4. doi: 10.1126/scitranslmed.aav5908.

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