The OI is reconstituted by exogenous IL-2, but not by IFN-γ. Four replicate plates were performed for OI as follows: (1) medium control, (2) medium containing 100 U/mL of IL-10, (3) medium containing 100 U/mL of IL-10 and 10 U/mL of IL-2, (4) medium containing 100 U/mL of IL-10 and IFN-γ. Four to 5 weeks later the transformation was visually scored. The results are expressed as OI index representing the minimum number of cells/well required to achieve 50% inhibition of EBV-induced transformation. One representative experiment of three is shown.