Early rheumatoid arthritis (ERA) differs from long-standing RA (LSRA) in circulating B cell subsets. changes according to disease activity under conventional therapy

Background: B cells have been shown to be important players in RA chronicity and B cell depletion has been shown to be effective in RF seropositive patients. No data are available on B cell subsets differences between ERA and LSRA. Objectives: To evaluate B cells subpopulations distribution in ERA patients and their possible association with clinical or immunological data at baseline or with response to therapy. Methods: 39 ERA (84.6% females; mean age 52.2±15.3 years; 81.1% anti-CCP positive, 67.6% IgM-RF positive, 43.2% IgA-RF positive) and 50 LSRA, along with 30 healthy blood donors were studied. Peripheral blood samples were analyzed by flow cytometry for the distribution of circulating B cell subpopulations by staining with surface markers CD19, CD45, CD38, CD27, IgD and intracellular marker ZAP70 (1). Plasma levels of IL-6 and BAFF were also determined with ELISAs. 14 ERA patients were followed for 6 months and baseline B subsets were compared to T6; they were treated with MTX (n=7) and MTX + TNF blockers (n=7). None received B cell depletion therapy. Results: Considering the Bm1-Bm5 classification, ERA patients showed an higher percentage of Bm2+Bm2' cells (49.1±20.6%) compared to LSRA patients (35.6±19.6%, p=0.003) and a lower percentage of eBm5 (9.5±5.2%) compared to LSRA (13.7±8.8%,p=0.02) and controls (16.0±7.1%, p<0.001). Moreover, the percentage of CD19+/IgD-CD27- cells (8.2±5.1%) and of CD19+/CD38+CD27+ cells (3.1±4.9%) was lower in ERA compared to LRSA (13.3±8.4%, p=0.02; 7.8±5.4%, p<0.001) and controls (16.2±9.1%,p<0.001; 8.0±3.4%, p<0.001). Patients with ERA showed a higher percentage of circulating CD19+/ZAP70+ cells (6.9±7.9%) compared to controls (2.2±1.4%, p=0.008), while no difference was seen between ERA and LSRA (p=ns). There were no differences in the distribution of circulating B cell subpopulations between patients RF and anti-CCP positive and patients seronegative. ERA patients with baseline moderate-high DAS (≥2.4) showed an higher ratio Bm2+Bm2'/eBm5+Bm5 (3.1±2.7) compared to subjects with baseline low DAS (<2.4) (1.4±1.0, p=0.05). The ratio Bm2+Bm2'/eBm5+Bm5 resulted lower in ERA patients with BAFF levels >75° percentile (2.5±3.7) vs subjects with levels <25°percentile (3.3±2.2, p=0.04). Moreover, plasmatic levels of BAFF at baseline correlated positively with percentage of CD19+/ZAP70+ cells (r=0.45, p=0.006), of CD19+/CD5+ cells (r=0.39, p=0.03) and of CD19+/CD23+ cells (r=0.46, p=0.02). In ERA patients followed for 6 months, we observed DAS falling from 3.6 to 1.7 (p<0.001), no changes in the Bm2-Bm2' and Bm5 subsets compared to baseline, while a statistically significant fall of percentage of CD19+/CD27+CD38+ cells (T0=4.3±6.6% vs T6=0.7±0.6%, p=0.002), and of CD19+/ZAP70+ cells (T0=10.4±10.3% vs T6=4.1±2.6%, p=0.01), irrespectively of the type of therapy administered. Conclusions: ERA differs from LSRA for higher levels of naive pre-switch B cells, lower levels of memory B cells and plasmablasts. After six months of treatment, a fall of plasmablasts and of ZAP70+ B cells was observed with conventional MTX (and/or TNF blockers) treatment. These results suggest that changing the inflammatory milieu leads to substantial changes in B cell subsets. The molecules involved need to be defined. References:[span] 1. Tolusso B et al. Clin Immunol 2009