Involvement of interleukin-18 (IL-18) in mixed lymphocyte reactions (MLR)

The in vitro mixed lymphocyte reaction (MLR) is a useful model to study alloresponsiveness to histocompatibility antigens. Secretion of different cytokine proteins in the supernatant of allo-MLR cultures has been reported in a few studies. We studied the levels of the cytokines interferon γ (IFN- γ) and interleukin-6 (IL-6), IL-10, IL-12, and IL-18 in the supernatant in allo-MLR by ELISA assay. Supernatant levels of IFN-γ, IL-6, IL-10, and IL-18 were detected at 12 h after MLR and markedly increased thereafter. In contrast, secretion of IL-12 was detected after 48-72 h. These results suggested that IFN-γ production depended on IL-18 in the early phase of MLR and depended on both IL-18 and IL-12 in the late phase. An antibody (Ab) neutralizing test was also performed. The levels of IFN-γ were significantly downregulated after the addition of anti-IL-18 Ab, anti-IL-12 Ab, or anti- IFN-γ Ab, and the levels of IL-12 were significantly downregulated after the addition of anti-IL-12 Ab and anti-IL-18 Ab. Treatment with these Ab did not suppress IL-6 production at all. The two-way MLR showed the same tendency as the one-way MLR. These results suggest the importance of IL-18 and IL-12 in allogeneic cell interactions and also suggest the usefullness of these Ab as regulators of alloresponsiveness.