The in vitro mixed lymphocyte reaction (MLR) is a useful model to study all
oresponsiveness to histocompatibility antigens. Secretion of different cyto
kine proteins in the supernatant of allo-MLR cultures has been reported in
a few studies. We studied the levels of the cytokines interferon gamma (IFN
-gamma) and interleukin-6 (IL-6), IL-10, IL-12, and IL-18 in the supernatan
t in allo-MLR by ELISA assay. Supernatant levels of IFN-gamma, IL-6, IL-10,
and IL-18 were detected at 12 h after MLR and markedly increased thereafte
r. In contrast, secretion of IL-12 was detected after 48-72 h. These result
s suggested that IFN-gamma 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-gamma were sig
nificantly downregulated after the addition of anti-IL-18 Ab, anti-IL-12 Ab
, or anti-IFN-gamma Ab, and the levels of IL-12 were significantly downregu
lated 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 show-ed
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 use
fullness of these Ab as regulators of alloresponsiveness.