title: 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.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: ImClone Systems Corp., New York, New York, USA. Nick.Loizos@ImClone.com
authors.forename: Nick
authors.initials: N
authors.lastname: Loizos
authors.forename: Leah
authors.initials: L
authors.lastname: Lariccia
authors.forename: Jami
authors.initials: J
authors.lastname: Weiner
authors.forename: Heather
authors.initials: H
authors.lastname: Griffith
authors.forename: Francesco
authors.initials: F
authors.lastname: Boin
authors.forename: Laura
authors.initials: L
authors.lastname: Hummers
authors.forename: Fredrick
authors.initials: F
authors.lastname: Wigley
authors.forename: Paul
authors.initials: P
authors.lastname: Kussie