The capacity of bone marrow-derived macrophages to process bovine insulin is regulated by lymphokines

The antigen presentation capacity of bone marrow-derived macrophages (BMMph) was shown previously to be increased after stimulation with the lymphokines IFN-γ or granulocyte macrophage colony stimulating factor (GM-CSF) respectively. Using bovine insulin (BI) as antigen, activation of BMMph with GM-CSF resulted in the generation of highly effective presenting cells. In contrast, IFN-γ-treated macrophages, although better presenters than untreated BMMph, stimulated Bispecific T hybridoma cells only weakly to IL-2 production despite the fact that they expressed drastically more MHC class II molecules than GM-CSF-activated BMMph. Therefore we analyzed whether the observed differences in the presentation function of GM-CSF- and IFN-γ-pulsed BMMph might be a consequence of differences in their capability to process BI. By blocking thiol and serine proteases with specific inhibitors or by raising the intracellular pH with chloroquine during BI pulse, the presentation capacity of IFN-γ-activated BMMph was significantly enhanced, while the presentation function of GM-CSF-pulsed macrophages was not positively influenced. These findings suggest that the activity of thiol/serine proteases in BMMph is differently influenced by the two cytokines. A regulatory influence of the cytokines on the activity of metallo and acidic proteases was not observed. Thus, the weaker BI presentation capacity of IFN-γ-treated macrophages as compared with GM-CSF-pulsed cells seems to be the consequence of a more excessive degradation of BI and destruction of the antigenic epitope.