Requirement of cell-to-cell contact for the inhibition of alloresponses.

The down-regulation of a naive alloresponse requires cell-to-cell contact with tolerized cells. Bm12-tolerized B6 CD4⁺ T cells were added directly to a primary B6 anti-bm12 MLR (permitting cell-to-cell contact) or were added to transwells (denying cell-to-cell contact but permitting the diffusion of soluble factors across a semipermeable membrane) suspended above the primary MLR at a ratio of 1 tolerized cell to 10 naive cells. The y-axis shows mean cpm ± 1 SE. On the x-axis are days in primary culture. A representative experiment of 3 is shown.