Monocyte-dependent stimulation of human T cells by silicon dioxide

Mononuclear cells were isolated by Ficoll-Hypaque density gradient centrifugation from randomly selected silicone breast implant recipients for testing. Restricted antibody to HLA-DR (28-33 kD) depleted the concanavalin A mitogenic response which was expected but failed to inhibit the proliferative response to silicon dioxide. Further testing with monoclonal antibodies to HLA-DP, -DQ, and a second -DR with specificity for the NS1 region of the MHC class II genome, all markedly inhibited proliferation of T cells despite otherwise adequate stimulation by concanavalin A or silicon dioxide. Monoclonal antibodies directed against B7-1 also inhibited proliferation of T cells following stimulation with concanavalin A or silicon dioxide. These results confirm the T-cell response to silicon dioxide is monocyte-dependent and not a superantigen as has been speculated.