Background The pathological basis in RA is synovitis characterized by hyperplasia of synovial lining and synovial stroma with neovascularisation and inflammatory infiltration. B-cell lymphoma (Bcl) 6 is a nuclear sequence-specific transcriptional suppressor and its target genes, such as p53, p27, have been reported overexpressed in RA synovium. However, little is known about Bcl6 expression and its significance in RA synovium.
Objectives To explore the correlation of synovial Bcl6 expression with synovitis and its components.
Methods Synovial tissue was obtained by arthroscopy or closed-needle biopsy from 45 active RA patients fulfilled the 1987 revised ACR criteria and 12 OA patients. Serial tissue sections were stained with H&E and IHC for Bcl6, CD3, CD20, CD38, CD68 and CD34. Percentage of lining Bcl6(+) cells and densities of sublining Bcl6(+) cells per mm2 were calculated. Three synovitis subscores (lining hyperplasia, inflammatory infiltration and stroma activation) were summarized to yield total synovitis score (≤4: low-grade synovitis; >4: high-grade synovits).
Results 1. Among 45 RA patients, 82% were female, median age was 55 years (range 23∼80), median disease duration was 36 months (range 2∼480), median DAS28 was 5.2 (interquartile range, IQR 4.4∼6.3) and the median synovitis score was 5 (IQR 4∼6). 2. In RA synovium, Bcl6 expressed strongly in the nuclei of synovial lining cells and sublining stroma cells including fibroblast, fibrocytes and endothelial cells (Fig.1). The median of lining Bcl6(+) cells percentage and sublining Bcl6(+) density was significantly higher than that in OA synovium (lining: 56% vs 25%, sublining: 1529 cells/mm2 vs 129 cells/mm2, both p<0.001). 3. Twenty-five patients had high-grade histological rheumatoid synovits and sublining Bcl6(+) density in high-grade synovits was significantly higher than that in low-grade synovits (median 1978 cells/mm2 vs 1297 cells/mm2, p<0.05). No significant difference of lining Bcl6 between these two groups (p>0.05). 4. Spearman's rank correlation test showed significant positive correlation of sublining Bcl6(+) cells density in RA synovium with total histological synovitis score, lining hyperplasia subscore, stroma activation subscore, CD34+ total vessels and microvessels densities (r=0.354∼0.412, all p<0.05), but not with inflammatory infiltration subscore, sublining CD3+T cells, CD20+ B cells, CD38+ plasmocytes and CD68+ macrophages (all p>0.05). 5. The Receiver operating characteristic (ROC) curve showed sublining Bcl6(+) density≥1666 cells/mm2 could discriminate high-grade synovitis from low-grade synovitis with sensitivity of 60% and specificity of 70% (AUC=0.694, P<0.05). RA synovium were divided into Bcl6 high-expression group (n=21) and Bcl6 low-expression group (n=24) according to this cutoff value. Lining hyperplasia subscore, stroma activation subscore, but not inflammatory infiltration subscore, in synovium with high-expression Bcl6 was higher than that with low-expression Bcl6 (all p>0.05).
Conclusions Our results showed over-expression of sublining Bcl6 correlated with hyperplasia of synovitis in RA. Together with similar reported expression of p53, it is speculated that Bcl6 may regulate the proliferation and apoptosis of synovial stromal and lining cells by regulating its downstream target genes.
Acknowledgements It was supported by Specialized Research Fund for the Doctoral Program of Higher Education (no.20130171110075), Guangdong Natural Science Foundation (no.S2013010014396), Medical Scientific Research Foundation of Guangdong Province, China (no. A2013201).
Disclosure of Interest None declared