Requirement for delivery of signals by physical interaction and soluble factors from accessory cells in the induction of receptor-mediated T cell proliferation. Effectiveness of IFN-gamma modulation of accessory cells for physical interaction with T cells.

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Abstract
We analyzed the mechanism by which accessory cells support the induction of the proliferation of human peripheral blood T cells by a monoclonal anti-CD3 antibody, OKT3. Cross-linking of T cell receptor/CD3 complex by anti-CD3 coupled to latex beads and the addition of IL-1 are not enough to induce the IL-2 production and proliferation of T cells extensively depleted of accessory cells, while the addition of both the culture supernatant of macrophages or a monoblastic cell line, U937 cells, and the paraformaldehyde-fixed macrophages or U937 cells which had been precultured with interferon-gamma before fixation into the culture of the T cells with anti-CD3-latex did induce the T cell proliferation. Lack of the addition of either one of these did not induce the response. These results indicate that the signal(s) delivered by soluble factors released from the accessory cells and that delivered by the physical interaction between accessory cells and T cells are both required for the induction of IL 2 production and proliferation of T cells by anti-CD3-latex. Importantly, the macrophages or U937 cells had to be cultured with Con A-stimulated lymphocyte culture supernatant or IFN-gamma prior to fixation with paraformaldehyde, suggesting that a molecule(s) inducible on accessory cells surface by IFN-gamma or other lymphokine is necessary for the effective accessory cell-T cell interaction to induce the T cell response. It was further revealed that the activity of the culture supernatant of accessory cells may be mediated synergistically by IL 1 and a certain other factor(s) and was actually shown to be replaced by the combined addition of rIL-1 and rIL-6 but not by rIL-1 alone. The experimental system described here will be very useful for dissecting the accessory functions for T cell activation.

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