MONOCYTE-REGULATED IFN-GAMMA PRODUCTION IN HUMAN T-CELLS INVOLVES CD2SIGNALING

Cooperation between monocytes and T lymphocytes is essential for sever al aspects of immunologic activation. We have utilized PHA and IL-2-ac tivated human T cells to characterize the role of monocytes in the reg ulation of T cell-derived IFN-gamma production. The limited IFN-gamma production by isolated T cells in this culture system was increased mo re than 10-fold when monocytes were added. No influence of monocytes w as observed on TNF production or T cell proliferation. Maximal level o f IFN-gamma in the cell culture supernatants was obtained when monocyt es were added within 12 h after activation of the T cells with IL-2 an d PHA. Addition of monocytes 48 h after activation resulted in margina l production of IFN-gamma, suggesting that T cells are sensitive to th e monocyte-related signal during a short time period after activation. Cell-to-cell contact between the T cells and accessory cells was foun d to be necessary for enhanced IFN-gamma production because separation of the cells with a semipermeable membrane abolished the effect. mAb blocking experiments suggested the involvement of the CD2/LFA-3 but no t the LFA-1/ICAM-1 pathway in monocyte regulation of T cell synthesis of IFN-gamma. Chinese hamster ovary (CHO) cells transfected with LFA-3 (CHO-LFA-3) and HLA-DR4/LFA-3 (CHO-DR4/LFA-3) strongly enhanced T cel l IFN-gamma production, whereas untransfected CHO cells, CHO cells tra nsfected with ICAM-1 (CHO-DR4/ICAM-1), and HLA-DR4 (CHO-DR4) did not s upport IFN-gamma production. PCR analysis and in situ hybridization de monstrated enhanced IFN-gamma mRNA levels in T cells stimulated in the presence of CHO-DR4/LFA-3 compared with untransfected CHO cells, indi cating that the CD2/LFA-3 pathway regulates IFN-gamma production at th e mRNA level. CHO-LFA-3 and CHO-DR4/ICAM-1 cells mediated strong adhes ion to T cells, whereas untransfected CHO tells and CHO-DR4 cells fail ed to mediate adhesion. This suggests that the ability of CHO-LFA-3 bu t not CHO-DR4/ICAM-1 cells to induce IFN-gamma production was attribut ed to signal transduction rather than cell adhesion only.