Lack of Detection of Agonist Activity by Antibodies to Platelet-Derived Growth Factor Receptor Alpha in a Subset of Normal and Systemic Sclerosis Patient Sera

Arthritis Rheum. 2009 Apr;60(4):1145-51. doi: 10.1002/art.24365.

Abstract

Objective: To investigate whether agonist anti-platelet-derived growth factor receptor alpha (anti-PDGFRalpha) 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 PDGFRalpha, PDGFRbeta, 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, PDGFRalpha-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 PDGFRalpha-expressing cell line.

Results: Sera from 34.3% of the healthy subjects and 32.7% of the SSc patients contained detectable autoantibodies to PDGFRalpha and PDGFRbeta, but not EGFR or CSFR1. Purified Ig from these sera was shown to retain PDGFR binding activity and, at 200-1,000 microg/ml, exhibited no agonist activity in a cell-based PDGFRalpha phosphorylation assay and did not stimulate a mitogenic response or MAP kinase activation in a PDGFRalpha-expressing cell line. Two purified Ig samples that were unable to bind PDGFRalpha did exhibit binding activity to a nonglycosylated form of PDGFRalpha.

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. PDGFRalpha agonist activity was not demonstrated when purified Ig from these sera was tested in cell-based assays.

MeSH terms

  • Adult
  • Aged
  • Antibody Specificity*
  • Autoantibodies / blood
  • Autoantibodies / immunology*
  • Autoantibodies / pharmacology
  • Cell Line
  • Female
  • Humans
  • MAP Kinase Signaling System / immunology
  • Male
  • Middle Aged
  • Mitogens / immunology
  • Phosphorylation / immunology
  • Receptor, Platelet-Derived Growth Factor alpha / agonists
  • Receptor, Platelet-Derived Growth Factor alpha / immunology*
  • Receptor, Platelet-Derived Growth Factor alpha / metabolism*
  • Receptor, Platelet-Derived Growth Factor beta / immunology
  • Scleroderma, Systemic / immunology*

Substances

  • Autoantibodies
  • Mitogens
  • Receptor, Platelet-Derived Growth Factor alpha
  • Receptor, Platelet-Derived Growth Factor beta