Effect of IL-10 on the outgrowth inhibitory capacity of CD4⁺ and CD8⁺ populations. CD4⁺- and CD8⁺-enriched PBL populations were obtained by negative depletion of CD8⁺ and CD4⁺ cells, respectively, and thereafter infected with EBV. OI assays were performed as described in medium alone or medium containing 100 U/mL of IL-10. 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.