Mesenchymal stromal cells (MSCs) represent a unique cell type with 
anti-proliferative effects on activated T and B cells. Based on our observation 
of differences between rheumatoid arthritis and osteoarthritis bone marrow B 
cells we hypothesized that rheumatoid arthritis bone marrow MSCs may enhance 
B-cell survival. We aimed to compare the effect of rheumatoid arthritis and 
osteoarthritis bone marrow-derived MSCs (rheumatoid arthritis MSCs, 
osteoarthritis MSCs) on the survival of healthy donor purified B cells. 
Rheumatoid arthritis and osteoarthritis MSCs were isolated from patients 
undergoing hip replacement surgery, and cultured in vitro for 2-5 passages. 
Washed cells were co-cultured with CD20+ B cells for 30-90 hours. Cell survival 
was analysed using 7-amino-actinomycin D labelling by flow cytometry. Expression 
of mRNA and protein was determined by RT-PCR and flow cytomery. Co-culture with 
both rheumatoid arthritis MSCs and osteoarthritis MSCs significantly enhanced 
B-cell survival, the effect being more prominent in rheumatoid arthritis MSCs. 
Both types of MSCs displayed expression of B cell-activating factor mRNA and 
protein. Blocking B cell-activating factor signalling from MSCs by specific 
anti-B cell-activating factor and anti-B cell-activating factor receptor 
antibodies weakly reversed the effect of MSCs on B-cell survival mainly in 
rheumatoid arthritis MSCs. MSC interaction with B cells provides stimuli for 
B-cell survival and therefore may contribute to the pathogenesis of rheumatoid 
arthritis. MSC-derived factors other than B cell-activating factor are likely to 
contribute to this effect. This feature is more prominent in rheumatoid 
arthritis MSCs, possibly due to the B cell-activating factor.