Expression of membrane-bound tumour necrosis factor (mTNF) after 4 hours of incubation with infliximab (Ifx). Cells stimulated for 6 days with purified protein derivative were incubated with Ifx (10 μg/ml) or a control monoclonal antibody at 4°C or at 37°C for 4 hours. Expression of mTNF on CD4+ T lymphocytes was then determined. (a) Results are expressed as mean fluorescence intensity (MFI) ± standard error of the mean from three experiments. (b) One of these experiments is shown.