Cytokine modulatable signalling through macrophage HLA class II. 1. IFN- γ upregulates the efficiency of Ca²⁺ mobilization in response to ligation of macrophage HLA-DP

The human macrophage line 2MAC, established recently from peripheral blood, expresses a number of lineage-specific markers as well as a broad array of intercellular adhesion molecules, including high levels of HLA class I and class II. We have presented evidence elsewhere that 2MAC can be productively applied to the study of signal transduction through macrophage HLA class II. Namely, we showed that ligation of 2MAC HLA class II, but not HLA class I, by monoclonal antibody (mAb) elicits an increase in free cytoplasmic Ca²⁺ concentration [Ca²⁺](i). Moreover, this Ca²⁺ flux appears to be functionally relevant: ligation of HLA-DR, but not HLA class I, by mAb results in the Ca²⁺ mobilization-dependent induction of tissue factor, the high-affinity cellular receptor for factor VII/VIIa. Here we show that 2MAC is uniquely valuable for addressing the efficiency of signal transduction through HLA class II. Namely, we show here that prior culture of 2MAC cells with interferon-γ (IFN-γ) profoundly upregulates subsequent Ca²⁺ mobilization in response to ligation of HLA-DP in the absence of increased cell surface HLA-DP expression. Because IFN-γ has no effect on 2MAC HLA-DP expression, IFN-γ must upregulate Ca²⁺ mobilization by increasing the efficiency of signal transduction through HLA class II (HLA- DP), by targeting some other component of the macrophage HLA class II signalling pathway.