MC transfer of OVA antigen to DCs results in T cell activation. MC/9 MCs were activated and incubated with DCs to facilitate antigen transfer. After 1 h of transfer, cells were spun down and co-cultured with 100 ng/ml LPS and T cells for 16 h. Cells were harvested and analyzed using flow cytometry. T cells (IgE⁻/CD11c⁻/CD3⁺/CD4⁺) were assessed for CD25 up-regulation. (A) T cells co-cultured with MCs not primed with IgE but in the presence of DNP-OVA and DCs. (B) T cells co-cultured with DCs in the presence of media from IgE-DNP-OVA–activated MCs (no MCs present). (C) T cells co-cultured with IgE-DNP-OVA–activated MCs. (D) T cells co-cultured with DNP-BSA–activated MCs and DCs. (E) T cells co-cultured with 100 µg/ml DNP-OVA–activated MCs and DCs. (F) T cells co-cultured with 10 µg/ml DNP-OVA–activated MCs and DCs. (G) T cells activated by DCs directly presenting OVA antigen. (H) T cells alone. Shown is one representative experiment of two.