Evaluation of neutrophil extracellular trap deregulated formation in pyoderma gangrenosum

Background and aim: Pyoderma gangrenosum is a neutrophilic dermatoses (ND) characterised by a dense neutrophilic infiltrate in the affected tissue. Neutrophil extracellular traps (NETs) are web-like structures released by neutrophils and composed of cytosolic and granule proteins assembled on a scaffold of decondensed chromatin. Although NETs have been implicated in the development of different autoimmune diseases, little is known about their role in ND.

The aim of this study was to evaluate the possible implication of NETosis in the pathogenesis of pyoderma gangrenosum compare to control groups.

Methods: Skin biopsies from 26 patients affected by pyoderma gangrenosum and 3 by sweet syndrome were analysed for NET expression by performing an MPO/H2B/DAPI immunofluorescence. Biopsies from 3 abscesses and 2 normal patients were also studied as controls. Neutrophils isolated from the blood of 3 pyoderma gangrenosum, 1 Sweet syndrome and 5 healthy controls were further analysed to assess the rate of spontaneous and induced NETosis by IF for MPO/DAPI.

Results: We found that all the lesions from PG patients and one out of the 3 SS displayed a highly increased level of NETosis. On the contrary, none of the control or abscess biopsies was instead positive for NET, although a variable level of H2B or MPO expression was found in abscesses and only H2B was detected in negative control skin. Neutrophils from peripheral blood of PG patients showed a significantly higher rate of spontaneous (but not induced) NETosis.

Conclusion: We demonstrated a significantly increased NETosis both in the affected tissue and in circulating neutrophils of PG patients compared to healthy subjects. NET is less frequently detected in SS patients, suggesting that despite a similar neutrophilic infiltrate in the skin neutrophilic dermatosis may differ in the extent of NETosis.Overall, this study suggests for the first time that the NETosis may contribute to tissue destruction and to disease progression in PG, thus representing a possible novel therapeutic target