PDGFRB and rheumatoid arthritis: The divergent correlation of PDGF-BB/PDGFR-β and TNF-α/LT-β with FDC developmental markers and RA synovial pathotypes demonstrated by the RNA-Seq analysis prompted the question “Can these correlations be recapitulated in vitro?” To answer this question, we stimulated RA synovial stromal cells (Figure 3A) with PDGF-BB or TNF-α/LT-αβ for 6 days then quantified the differential expression of FDC differentiation genes.