Bactericidal/permeability-increasing protein and cathepsin G are the major antigenic targets of antineutrophil cytoplasmic autoantibodies in systemic sclerosis.

OBJECTIVE: To study the prevalence and antigenic specificity of antineutrophil cytoplasmic autoantibodies (ANCA) in patients with systemic sclerosis (SSc).
METHODS: Sera from 68 patients with SSc were screened for ANCA by indirect immunofluorescence (IIF) assay and for antibodies to myeloperoxidase (MPO) by ELISA. All sera positive for ANCA on IIF were analyzed for reactivity against antigenic targets other than MPO [bactericidal/permeability-increasing protein (BPI), cathepsin G, lysozyme, elastase, PR3, and lactoferrin]. Twenty-three sera negative for ANCA were also tested for antibodies to BPI and cathepsin G using ELISA.
RESULTS: The study included 33 patients with diffuse and 35 with limited SSc. ANCA was detected in 24 of the 68 sera (35.3%). In these 24 sera the antigenic targets were BPI in 14, cathepsin G in 13, and MPO in 8. Sera of 11 patients had reactivity against both BPI and cathepsin G. In sera, that were negative for ANCA, antibodies to BPI (4/23), cathepsin G (3/23), and MPO (1/44) were found in a small proportion of patients. Patients with antibodies to BPI had lower skin score, whereas no patient with antibodies to MPO had renal disease.
CONCLUSION: BPI and cathepsin G are the major antigenic targets of ANCA seen in patients with SSc. Patients with antibodies to BPI had lower skin scores.