Monocyte-specific gene signatures in rheumatoid arthritis

Background

In rheumatoid arthritis (RA), monocytes are of central importance in the chronic inflammatory immune response. These cells may display diagnostic markers and provide insight into pathophysiological pathways in RA.

Objective

To identify characteristic expression patterns in rheumatoid arthritis (RA), highly purified peripheral blood monocytes were investigated.

Methods

Monocytes from five normal donors (ND) and six patients with active RA were purified by erythrocyte lysis and CD14-positive selection at constant low temperature (4°C) conditions to minimize in vitro induced artefacts. Gene expression was detected by Affymetrix HG U133A hybridization. Bioinformatic analysis included MAS5.0 image analysis, statistical methods (t-test; Mann-Whitney) and cluster analysis (genes@work).

Results

Array analysis revealed about 50% present calls in ND or RA monocytes. MAS5.0 comparison expression analysis revealed 605 genes that were significantly changed in more than 50% of all RA versus ND pair-wise comparisons. Statistical methods revealed that 260 of these genes were significantly different (P < 0.05). Selection and reduction by fold changes above 1.6 and statistical methods reduced the number of differentially expressed genes to 152. This set of genes is implicated in cellular processes that are involved in cell communication (cytokines, chemokines and their receptors), intracellular signalling, transcription, defense response, apoptosis and heat shock responses. Hierarchical cluster analysis based on these selected genes separated into two branches, one for ND and one for RA patients.

Conclusion

Gene expression profiling of separated peripheral blood monocytes identified a characteristic gene pattern that is involved in the activation of monocytes, and clearly indicates an inflammatory process in RA. These results will be compared with expression profiles in other inflammatory rheumatic diseases and further analyzed for dominant pathophysiological pathways in a search for new candidates for targeted therapy in RA.