Kinetics of interferon-γ secretion and its regulatory factors in the early phase of acute graft-versus-host disease

Increased serum levels of interferon-gamma (IFN-gamma) have been observed in acute graft-versus-host disease (GVHD). Recent in vitro studies have demonstrated that interleukin-12 (IL-12) and interleukin-18 (IL-18) synergistically up-regulate IFN-gamma secretion. In this communication, we investigated the factors relevant to IFN-gamma secretion in acute GVHD. A murine model of acute GVHD was established by injecting donor spleen cells into severe combined immunodeficiency (SCID) mice. A series of specimens, including sera, livers and spleens derived from the GVHD mice, were investigated with histological examination, enzyme-linked immunosorbent assay (ELISA), flow cytometry, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). IFN-gamma secretion increased in serum 3 days after spleen cell transfer, peaked on day 7, and then gradually decreased close to the baseline level by day 35. A synchronized increase of activated T cells and mRNA expression of IL-12, IL-18 and their respective receptors was observed after spleen cell transfer. However, only the kinetic expression pattern of IL-12 receptor (IL-12R) beta 2 chains was closely correlated with that of IFN-gamma, while IL-12 dropped to the baseline level earlier than IFN-gamma. Therefore, IFN-gamma expression in the early phase of acute GVHD is a mono-peak and self-restricted pattern. Its secretion is closely related with T-cell activation, the presence of IL-12, IL-18 and their respective receptors. However, the limiting factors for IFN-gamma secretion seem to be IL-12 and IL-12R beta 2 chains.