Monoclonal antibody two-site ELISA for human IFN-gamma. Adaptation for determinations in human serum or plasma.

Mouse monoclonal antibodies (mAbs) against human interferon-gamma (IFN-gamma) were produced after immunization with recombinant IFN-gamma. Two mAbs (1-D1K and 7-B6-1) recognizing distinct epitopes on natural IFN-gamma were selected for the development of a two-site ELISA. The sensitivity was similar for IFN-gamma diluted in PBS with 1% bovine albumin, spent culture medium or fetal calf serum but reduced to approximately 50% when diluted in normal human serum. Individual normal human sera were tested and three of 14 gave false reactivities in the ELISA. One serum factor with major impact on the individual variation and the decreased sensitivity could be adsorbed to and eluted from protein A-Sepharose. Based on these observations we established a new ELISA protocol which made it possible to test for low levels of IFN-gamma in human serum and plasma samples. The modifications in this protocol are easy to apply with basic laboratory equipment.