DR*0401-dependent killing of B-LCLs by BHRF1-specific CD4 T-cell clones. (A) Two PBL-derived clones from the healthy donor D3 (LP15 and LP45) and 2 SF-derived clones (A22 and G4) killed a DR*0401 B-LCL, either unloaded or loaded with PYY peptide, while they did not kill an unloaded DR*0404 B-LCL. The 2 SF-derived clones, but not the PBL-derived clones, killed the DR*0404 B-LCL after loading with PYY peptide. Results are expressed as percent specific lysis at E/T ratio 10:1. (B) The CD4 T-cell clone A22 was tested against a panel of 5 DR*0401⁺ (black symbols) and 3 DR4^– (open symbols) unloaded B-LCLs. All DR*0401⁺ B-LCLs were killed, while DR4^– B-LCLs were not.