TGF-β suppresses antigen stimulation of a uveitogenic T cell line through an effect on antigen-presenting cells

Purpose: Numerous studies have implicated the suppressive cytokine TGF-β1 as having a central role in the control of cell-mediated autoimmunity. We therefore wished to examine the effect of TGF-β1 on stimulation of the highly uveitogenic rat T cell line SP35, specific to peptide 35 of the retinal S-Antigen. Methods: SP35 cells were stimulated through the T cell receptor (TCR) in the presence or absence of TGF-β1, by one of two methods; peptide presented on syngeneic antigen-presenting cells (APC), or crosslinking of CD3 plus CD28 engagement by specific monoclonal antibodies. Proliferation assays were done in 96-well flat-bottom plates. For peptide/APC-driven stimulation, SP35 cells (2x104/well) were cultured with peptide (2μg/ml) and APC (5x105/well). For anti-CD3/anti-CD28 stimulation, SP35 cells (2x104/well) were cultured in wells precoated with 1 μg/ml anti-CD3, in the presence of 5 μg/ml anti-CD28. TGF-β was added in serial dilutions ranging from 0.08 to 10 ng/ml. Cultures were incubated for 60 h and were pulsed with 3H-thymidine for the last 20 hours. Results: TGF-β1 concentrations ≥ 0.15 ng/ml reproducibly suppressed antigen/APC-driven proliferation of SP35 cells by up to 50%. The level of suppression appeared to remain constant over a range of APC concentrations from 1x105 to 5x105 cells/well at a TGF-β1 concentration of 1 ng/ml. No suppression was seen when SP35 cells were stimulated by ant -CD3/anti-CD28, even at 10ng of TGF-β1. Conclusions: TGF-β1 can partially suppress the response of uveitogenic SP35 line cells to TCR-mediated stimulation. The inhibition seems to be exerted at the level of the APC's, since stimulation by monoclonal antibodies was not suppressed. The suppression plateaued at 30-50%, suggesting a selective effect on a noncritical APC function(s). We believe that additional mechanisms to inhibition of antigenic stimulation of pathogenic effector T cells must be invoked to explain the central role attributed to TGF-β in the control of cell-mediated autoimmunity in vivo.

Duke Scholars

Author Teresa Kathleen Tarrant Medicine, Rheumatology and Immunology