Standardization of GST capture assay. GST chimeric proteins diluted in normal mouse serum were tested in the GST capture assay described under Materials and Methods. Mean optical density values are shown (SD values did not exceed 10% of mean values in any case; not shown). TS-SAPA and cruzipain protein diluted in normal mouse serum were used as negative controls. Samples were tested in triplicate. One out of three experiments with similar results is shown.