HUMAN EOSINOPHIL CYTOTOXICITY-ENHANCING FACTOR - EOSINOPHIL-STIMULATING AND DITHIOL REDUCTASE ACTIVITIES OF BIOSYNTHETIC (RECOMBINANT) SPECIES WITH COOH-TERMINAL DELETIONS

U937 cells produce eosinophil cytotoxicity-enhancing factor (ECEF) pol ypeptides of 14 and 10 kDa that have identical NH2-terminal amino acid sequences. The 10-kDa form has greater eosinophil-stimulating activit y (half-maximal at >20-fold lower concentration). We considered the hy pothesis that there is a precursor-product relationship between the 14 - and 10-kDa species. Recombinant 14-kDa 104-amino acid ECEF (rECEF-10 4) had a slight stimulatory effect on eosinophil cytotoxic function at concentrations of 160 nm and above. In contrast, two species, rECEF-8 0 and rECEF-84, representing cleavage products of approximately 10 kDa had substantial statistically significant cytotoxicity-enhancing acti vity at concentrations as low as 10 pm. This evidence demonstrates the potential to generate the high-activity ECEF species by proteolytic c leavage of the 104-amino acid species. Another feature of this cytokin e is the sequence from amino acids 31 to 34, which constitutes the con served and active site of the enzyme thioredoxin. When tested for dith iol reductase enzymatic activity, rECEF-104 was active in a dose- and time-dependent manner, whereas the truncated forms of the molecule had no dithiol reductase activity. Thus the eosinophil-stimulating functi ons of the molecule do not correlate with its enzymatic activity. The evidence shows that the enzymatic activity is not essential for the in itial interaction of ECEF with the eosinophil, and it suggests that th e ECEF molecule functions by means of two discrete mechanisms.