The monoclonal antibody MAC387 detects an epitope on the calcium-binding protein MRP14

The present study was initiated to identify the antigen recognized by the monoclonal antibody (MAb) MAC387 which is widely used for phenotypical characterization of myelomonocytic cells in situ. MAC387 has been described to show a similar reaction pattern as antisera to a complex formed by the calcium-binding proteins MRP8 and MRP14. However, the exact nature of the molecule recognized by MAC387 has been controversial. Using Western blot analysis, MAC387 was found to detect a single protein band of 14 kDa in lysates of human monocytes and granulocytes. Transfection of embryonic lung fibroblasts L132 with either MRP8 or MRP14 cDNA revealed that MAC387 reacts with MRP14 but not MRP8. This finding was confirmed by dot blot analysis of recombinant MRP8 and MRP14. Our data thus provide unequivocal evidence that MAC387 is a monoclonal antibody directed against the calcium-binding protein MRP14.