Figure 1.

Coculture-conditioned medium is selectively depleted of tryptophan. Human monocytes were allowed to differentiate for 5 d in MCSF. Then, T cells were added and activated with anti-CD3 mAb. Conditioned medium was harvested from cocultures after 48 h and then used to support a second round of activation with fresh T cells. Replicate cultures were supplemented with individual amino acids to the concentrations normally found in RPMI 1640. Control cultures received either fresh medium (CTL) or no supplement (PBS). Proliferation was measured by thymidine incorporation after 72 h.