| Abstract: | Objective To investigate whether agonist anti–platelet‐derived growth factor receptor α (anti‐PDGFRα) antibodies are present in the serum of patients with systemic sclerosis (SSc; scleroderma). Methods Sera were obtained from healthy subjects and scleroderma patients. An electrochemiluminescence binding assay was performed for detection of serum autoantibodies to PDGFRα, PDGFRβ, epidermal growth factor receptor (EGFR), and colony‐stimulating factor receptor 1 (CSFR1). Serum immunoglobulin was purified by protein A/G chromatography. To assess Ig agonist activity, PDGFRα‐expressing cells were incubated with pure Ig and the level of receptor phosphorylation determined in an enzyme‐linked immunoassay, as well as by Western blotting. Ig agonist activity was also assessed in a mitogenic assay and by MAP kinase activation in a PDGFRα‐expressing cell line. Results Sera from 34.3% of the healthy subjects and 32.7% of the SSc patients contained detectable autoantibodies to PDGFRα and PDGFRβ, but not EGFR or CSFR1. Purified Ig from these sera was shown to retain PDGFR binding activity and, at 200‐1,000 μg/ml, exhibited no agonist activity in a cell‐based PDGFRα phosphorylation assay and did not stimulate a mitogenic response or MAP kinase activation in a PDGFRα‐expressing cell line. Two purified Ig samples that were unable to bind PDGFRα did exhibit binding activity to a nonglycosylated form of PDGFRα. Conclusion Although approximately one‐third of sera from scleroderma patients contained detectable autoantibodies to PDGFR, these antibodies were not specific to scleroderma, since they were also detected in a similar percentage of samples from normal subjects. PDGFRα agonist activity was not demonstrated when purified Ig from these sera was tested in cell‐based assays. |
