Elevated levels of eosinophil major basic protein in the sera of patients with systemic sclerosis

Objective. To examine eosinophil activation, as reflected by evidence of eosinophil degranulation in the blood and affected tissues, in patients with diffuse and limited cutaneous forms of systemic sclerosis (SSc). Methods. Levels of the eosinophil‐derived major basic protein (MBP), a marker of eosinophil degranulation, were determined in sera from 46 SSc patients, from patients with rheumatoid arthritis and giant cell arteritis, and from healthy volunteers, and in bronchoalveolar lavage fluid from 4 SSc patients. Extracellular tissue deposition of MBP was evaluated in biopsy specimens from affected skin or lung of 11 SSc patients. Results. Patients with diffuse cutaneous SSc (dcSSc) had elevated serum MBP levels compared with normal individuals (mean ± SD 762 ± 271 ng/ml versus 534 ± 144 ng/ml; P = 0.0004). MBP levels were positively correlated with the extent of cutaneous involvement, and negatively correlated with pulmonary function and duration of disease (r = –0.20). By immunohistochemical analysis, modest extracellular MBP deposition could be demonstrated in involved skin in 7 of 10 biopsy specimens, and MBP staining was prominent in affected lung tissues in 2 patients. Conclusion. Eosinophil degranulation appears to be increased in some patients with dcSSc, as indicated by elevated serum levels of MBP and extracellular accumulation of MBP in the lung. Eosinophil granule proteins may contribute to the development of cutaneous and pulmonary fibrosis in SSc.