Fibroblast recognition by HLA-class II–restricted T cells. Primary fibroblasts of the patient were cultured with and without addition of 100 IU/mL IFN-γ. (A) Up-regulation of HLA-DR, -DQ, and -DP was measured by flow cytometry after 5 days of IFN-γ treatment. (B) T-cell recognition of pretreated and untreated fibroblasts was tested in an IFN-γ ELISA. A CD8⁺ T-cell clone (4D8) recognizing an unknown mHag in HLA-B8 served as positive control. Mean release of IFN-γ (ng/mL) in 50-μL supernatants of duplicate wells is shown.