Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


BAFF Expression on the Surface of RA Synovial Fibroblasts (RASFib) Facilitates B Cell Responses to IL-15.

Garcia-Carmona,  Yolanda, Benito-Miguel,  Marta, Balsa,  Alejandro, Martin-Mola,  Emilio, Eugenia Miranda-Carus,  Maria

Background:

We previously described that IL-15 expressed on RASFib significantly contributes, by a cell-contact dependent mechanism, to the anti-apoptotic action of RASFib on B cells. In addition, whereas exogenous recombinant IL-15 (rhIL-15) has a minimal effect on isolated B cell survival, it significantly potentiates the anti-apoptotic effect of RASFib on B cells. This is attributable to an RASFib-mediated upregulation of the B cell IL-15 receptor.

Objectives:

BAFF, a B cell survival factor expressed on RASFib, was tested as a potential candidate involved in upregulating B cell IL-15R.

Methods:

Magnetically sorted peripheral blood memory B cells from 20 healthy subjects (CD19+CD20+CD27+, purity >96%) were cultured in the presence or absence of rhIL-15, recombinant human BAFF (rhBAFF), or a combination of both. In addition, B cells were cocultured with RASFib from synovectomy or arthroplasty specimens (n= 10) in the presence or absence of rhIL-15, with or without BAFF neutralizing agents.

Results:

Survival of isolated B cells cultured for 6 days in plain medium was below 1% (annexin V-7AAD and JC-1 staining). RhIL-15 had a minimal effect on isolated B cell survival. In contrast, culture of B cells in the presence of rhBAFF resulted in significantly increased survival (22.3+/-3.2% viable cells at 6 days, p<0.001) together with upregulation of all three IL-15R chains; in parallel, rhIL-15 potentiated the anti-apoptotic effect of BAFF (32.7+/-4.4% viable cells at 6 days, p<0.05).

Flow cytometry of RASFib detached with PBS-EDTA demonstrated surface expression of BAFF together with surface IL-15. In parallel, coculture with RASFib dramatically prolonged B cell survival (55.3+/-8.1% viable cells at 6 days, p<0.01) and at the same time upregulated B cell expression of IL-15Ra, b and g chains. RhIL-15 potentiated the anti-apoptotic effect of RASFib (75.1+/-5.2% viable cells, p<0.05). In the presence of BAFF neutralizing agents (an anti-BAFF MoAb or a BAFFR-Fc), the effect of RASFib on both B cell survival and B cell expression of IL-15 R was significantly attenuated (28.1+/-4.5 or 27.3 +/-3.8 viable cells, respectively, p<0.05). In parallel, rhIL-15 had a lower effect on the survival of B cells cocultured with RASFib in the presence of BAFF neutralizing agents (62.3+/-8.2% viable cells, p<0.05 vs conditions without BAFF neutralization). IL-15 blocking agents were not additive with BAFF neutralization in Bcell/RASFib cocultures (28.3+/-4.2% viable cells). In contrast, in the absence of BAFF antagonists, neutralization of IL-15 (with an anti-IL-15 MoAb or an antagonistic IL-15 mutant/Fcg2a fusion protein) was effective at decreasing the antiapoptotic effect of RASFib on B cells (35.5+/-6.2% or 32.8+/-5.7% viable cells, respectively, p<0.01). Isotype control MoAbs or Fc fusion proteins used as negative controls had no effect. This indicates that constitutive surface IL-15 expression on RASFib contributes to extending the survival of cocultured B cells when constitutive BAFF activity is spared.

Conclusion:

The antiapoptotic effect of RASFib surface IL-15 on cocultured B cells is facilitated by RASFib surface BAFF, through an upregulation of IL-15Ra, b and g chain expression.

To cite this abstract, please use the following information:
Garcia-Carmona, Yolanda, Benito-Miguel, Marta, Balsa, Alejandro, Martin-Mola, Emilio, Eugenia Miranda-Carus, Maria; BAFF Expression on the Surface of RA Synovial Fibroblasts (RASFib) Facilitates B Cell Responses to IL-15. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :349
DOI: 10.1002/art.28118

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