SpotLight Proteomics-A IgG-Enrichment Phenotype Profiling Approach with Clinical Implications

Int J Mol Sci. 2019 May 1;20(9):2157. doi: 10.3390/ijms20092157.


Sarcoidosis is a systemic interstitial lung disease of unknown aetiology. Less invasive diagnostics are needed to decipher disease pathology and to distinguish sub-phenotypes. Here we test if SpotLight proteomics, which combines de novo MS/MS sequencing of enriched IgG and co-extracted proteins with subsequent label-free quantification of new and known peptides, can differentiate controls and sarcoidosis phenotypes (Löfgrens and non-Löfgrens syndrome, LS and nonLS). Intra-individually matched IgG enriched from serum and bronchial lavage fluid (BALF) from controls (n = 12), LS (n = 11) and nonLS (n = 12) were investigated. High-resolution mass-spectrometry SpotLight proteomics and uni- and multivariate-statistical analyses were used for data processing. Major differences were particularly observed in control-BALF versus sarcoidosis-BALF. However, interestingly, information obtained from BALF profiles was still present (but less prominent) in matched serum profiles. By using information from orthogonal partial least squares discriminant analysis (OPLS-DA) differentiating 1) sarcoidosis-BALF and control-BALF and 2) LS-BALF vs. nonLS-BALF, control-serum and sarcoidosis-serum (p = 0.0007) as well as LS-serum and nonLS-serum (p = 0.006) could be distinguished. Noteworthy, many factors prominent in identifying controls and patients were those associated with Fc-regulation, but also features from the IgG-Fab region and novel peptide variants. Differences between phenotypes were mostly IgG-specificity related. The results support the analytical utility of SpotLight proteomics which prospectively have potential to differentiate closely related phenotypes from a simple blood test.

Keywords: IgG; Löfgrens syndrome; biomarker; sarcoidosis.

MeSH terms

  • Adult
  • Biomarkers / analysis
  • Biomarkers / blood
  • Bronchoalveolar Lavage Fluid / chemistry
  • Female
  • Humans
  • Immunoglobulin G / blood*
  • Male
  • Middle Aged
  • Phenotype
  • Proteome / chemistry*
  • Proteome / metabolism
  • Sarcoidosis / blood*
  • Sarcoidosis / metabolism


  • Biomarkers
  • Immunoglobulin G
  • Proteome