Primary mixed lymphocyte reaction (MLR) cultures were established with naive B6 CD4⁺ T cells as responders and irradiated, T-cell-depleted bm12 splenic stimulators. Tolerized cells were directly added to some wells of the primary MLR, permitting cell-to-cell contact, or were added with stimulators to transwells suspended above the MLR, permitting the diffusion of soluble factors but denying direct cell-to-cell contact. A ratio of 1 tolerized cell to 10 naive B6 CD4⁺ T cells was used. Supernatants were harvested on days 4 and 6 of culture. These data were reproduced in a second experiment. Final concentration of naive B6 CD4⁺ T cells was 0.5 × 10⁶ cells per milliliter. Values are in pg per milliliter, and sensitivity of the enzyme-linked immunosorbent assay is 3.0 pg/mL.