Activated human T-cells bestow T-cell antigens to non-T-cells by intercellular antigen transfer

The mechanism of the appearance of T-cell antigens on B-cells, following in vitro activation of peripheral blood lymphocytes, was analyzed using the following model: Purified T-cell suspensions were activated by exposure to phytochemagglutinin (PHA) for 3 days, and then incubated for one hour in the presence of cells of either Raji or K562 cells. The expression of T-cell antigens on the cell lines was determined using immunofluorescent F(ab)2 fragments of monoclonal antibodies (mAbs). Following exposure of the CD19⁺ Raji cells to activated T lymphocytes, 87.6% of the CD19⁺ cell co-expressed CD2. A large proportion of the CD19⁺ cells also expressed CD4, CD5, and CD8 antigens. Similar results were obtained with Raji cells that were prelabeled with calcein AM. In Raji cells, which were rendered CD5⁺ following incubation with activated T cells, only a negligible level of CD5 mRNA was detected with a sensitive RT-PCR technique, probably attributable to contamination with T cells. K562 cells incubated with activated T cells acquired CD2 but not the CD4 and CD8 antigens. Exposure of either Raji or K562 cells to mAb against CD58 inhibited the transfer of CD2. The present study indicates that following their activation, T-cells gain the capacity to transfer T-cell antigens to non-T cells and that CD2 and CD58 molecules are involved in this process.