Background Systemic lupus erythematodes(SLE) causes various symptoms in the respiratory system. Ground glass opacity (GGO) with SLE is conventionally considered interstitial pneumonia caused by the deposition of immune complexes. However, in most cases, ground glass opacity is not related to disease activity or inflammation. It is thus hypothesized that GGO is due to pulmonary alveolar proteinosis (PAP).

Objectives Anti-Granulocyte Macrophage colony-stimulating Factor(GM-CSF) autoantibody is a cause of PAP. We therefore measured anti-GM-CSF autoantibody in sera of patients with SLE to test the hypothesis that PAP occurs in lupus pulmonary disease.

Methods The samples were obtained from a total of 64 japanese patients in our hospital. They were diagnosed according to the 1997 criteria for SLE. The enzyme-linked immunosorbent assay was performed according to a modified version of the method described previously (1) with sera being diluted 100-fold with phosphate-buffered saline.

50μl diluted sera were transferred to a plate coated with 1μg/ml of GM-CSF (Escherichia coli derived) and the plate was kept at 4 degrees temperature for 8 h. After washing, autoantibodies captured by GM-CSF were detected by peroxidase-labeled anti-human IgG antibodies. Color was detected using o-Phenylenediamine and the absorbance was measured at 450 nm.

Results Anti-GM-CSF autoantibodies were detected in 53 percent of SLE patients, with the cuttoff level being 2SD (standard deviation) of the value of the healthy serum. The titers varied, and were significantly higher in SLE patients than in patients with systemic scleroderma. Furthermore, GGO in high-resolution CT was significantly related to the anti-GM-CSF autoantibody titers (p=0.01). The patient with the highest titers had decreased respiratory function with massive ground glass opacity in both lungs. Bronchoalveolar lavage was performed, and PAP was confirmed.

The presence of anti-GM-CSF autoantibodies may be a predictor of the onset of PAP because increased levels of autoantibodies were detected two years prior to onset of pulmonary disease in this patient.

Conclusions This is the first report to systematically measure anti-GM-CSF autoantibodies in patients with SLE. PAP was present in pulmonary disease that was conventionally considered interstitial pneumonia in patients with SLE.

It is important to measure anti-GM-CSF autoantibodies because the treatment differs for PAP and interstitial pneumonia in patients with SLE.

References

1. Kitamura, T et al. 1999. Idiopathic pulmonary alveolar proteinosis as an autoimmune disease with neutralizing antibody against granulocyte. macrophage colony stimulating factor. J. Exp. Med. 190:875.880.

Disclosure of Interest: None Declared