SIRPβ2-CD47 interaction enhances superantigen-mediated T-cell proliferation and costimulates T-cell activation. (A) The CD4⁺ SIRPβ2⁺ Vβ3⁺ T-cell clone Vβ3Φ was incubated with irradiated B lymphoblastoid cells RPMI 8866 that had been pulsed with serial dilutions of SEE (ng/mL). Anti-CD47 (▵), anti-SIRPβ2 (○), or control mouse antibodies (•) were added to T/B-cell cocultures as indicated. T-cell proliferation was measured by ³H-thymidine incorporation assay. (B-C) Blockade of SIRPβ2-CD47 interaction with mAbs partially inhibits T-cell proliferation and IFN-γ production triggered by allogeneic immature DCs in MLCs. Symbols represent same as in panel A; in addition, ▪ indicates medium, and ⋄, 148. (D) CD4⁺ T cells purified from peripheral blood were plated on serial dilution of anti-CD3 antibody (μg/mL) in the presence of fixed amounts of mAbs against SIRPβ2 (▵), CD28 (○), or control IgG (•). T-cell proliferation was measured after 72 hours as described.