Neutrophil respiratory burst is decreased in scleroderma and normalized by near-infrared mediated hyperthermia

The production of reactive oxygen species (ROS) by fibroblasts has been suggested to contribute to scleroderma pathogenesis. Infrared-mediated hyperthermia has recently been shown to be of benefit in scleroderma.

As the contribution of neutrophils and monocytes to ROS formation in scleroderma is unknown, we studied respiratory burst in these cell types. We also aimed to test the hypothesis that near-infrared (IRA) treatment may effect burst activity.

We determined respiratory burst in patients with scleroderma (n = 22) and age- and sex-matched controls (n = 20) at baseline, and after high-level stimulation by phorbolmyristyl acetate (PMA) and low-level stimulation by non-opsonized zymosan. Respiratory burst was also assessed before and after a series of infrared-mediated hyperthermia treatments.

Unexpectedly, we observed no increase but instead a slight but statistically significant reduction in baseline and zymosan-stimulated respiratory burst in scleroderma neutrophils (P < 0.001) and monocytes (P < 0.005). This decrease in burst activity was nonspecific, as it was also observed in patients with another active inflammatory disease, psoriasis. IRA treatment induced a cell-type-specific normalization of respiratory burst only in neutrophils, but not in monocytes. Intriguingly, neutrophil-specific normalization of ROS formation persisted for 6 weeks after the end of IRA treatment, in concordance with the previously reported clinical responses to this therapy.

Neutrophils and monocytes do not exhibit cell-autonomous overproduction of ROS in scleroderma, thereby implicating fibroblasts as main source for clinically relevant ROS accumulation. Furthermore, repeated mild infrared-mediated hyperthermia exerts a lasting cell-type-specific effect on neutrophils.