Leucocyte activation in erythema nodosum.

As a neutrophilic vascular reaction of small vessels in the subcutaneous tissue and a neutrophilic inflammatory infiltrate are common histopathological features found in initial erythema nodosum (EN) lesions, we asked the question whether activated polymorphonuclear neutrophils (PMN) might play a role in the pathogenesis of EN. We analysed the production of reactive oxygen intermediates (ROI) as a marker for activated neutrophils in the peripheral blood of patients suffering from EN (n = 10) and healthy volunteers (n = 10). FACS analysis of dihydrorhodamine 123-stained PMN was used to detect ROI production due to respiratory burst activity. Patients suffering from EN had a fourfold higher percentage of preactivated ('primed') ROI-producing PMN compared with healthy volunteers. Activation of PMN with formylated methionyl-leucyl-phenylalanine and phorbol 12-myristate 13-acetate led to an increase of ROI production per cell but had no influence on the percentage of activated cells. The percentage of ROI-producing cells in patients with EN correlated with the clinical severity. From these data, we conclude that ROI might play a role in the pathogenesis of EN. ROI might exert their effects by oxidative tissue damage and by promoting tissue inflammation.