Assessment of serum biomarkers extrapolated from lymphoid and myeloid synovial phenotype gene expression in the synovial transcriptome training dataset. Intercellular adhesion molecule 1 (ICAM1) (A) and C-X-C motif chemokine 13 (CXCL13) (B) genes are expressed at highest levels in the myeloid (M) and lymphoid (L) phenotypes respectively. Array probes for each transcript were compared across all groups using the f-test, and in both cases Benjamini-Hochberg-corrected, *P < 0.001. X = low inflammatory phenotype and F = fibroid phenotype. Soluble (s)ICAM1 (C) and CXCL13 (D) are elevated in serum samples from rheumatoid arthritis (RA) patients (ADACTA trial) as compared with normal control (NC) serum. P-values derived from the Wilcoxon test are indicated. (E) Serum sICAM1 and CXCL13 levels were only weakly correlated in RA (ρ < 0.33, Spearman rank correlation coefficient).