Murine Aortic Smooth Muscle Cells Acquire, Though Fail to Present Exogenous Protein Antigens on Major Histocompatibility Complex Class II Molecules

In the present study aortic murine smooth muscle cell (SMC) antigen presentation capacity was evaluated using the E alpha-GFP/Y-Ae system to visualize antigen uptake through a GFP tag and tracking of E.. peptide/MHCII presentation using the Y-Ae Ab. Stimulation with IFN-gamma (100 ng/mL) for 72 h caused a significant (P < 0.01) increase in the percentage of MHC class II positive SMCs, compared with unstimulated cells. Treatment with E alpha-GFP (100 mu g/mL) for 48 h induced a significant (P < 0.05) increase in the percentage of GFP positive SMCs while it did not affect the percentage of Y-Ae positive cells, being indicative of antigen uptake without its presentation in the context ofMHC class II. After IFN-gamma-stimulation, ovalbumin-(OVA, 1 mg/mL) or OVA(323-339) peptide-(0.5 mu g/mL) treated SMCs failed to induce OT-IICD4(+) T cell activation/proliferation; this was also accompanied by a lack of expression of key costimulatory molecules (OX40L, CD40, CD70, and CD86) on SMCs. Finally, OVA-treated SMCs failed to induce DO11.10-GFP hybridoma activation, a process independent of costimulation. Our results demonstrate that while murine primary aortic SMCs express MHC class II and can acquire exogenous antigens, they fail to activate T cells through a failure in antigen presentation and a lack of costimulatory molecule expression.