DETECTION OF ADULT T-CELL LEUKEMIA-DERIVED FACTOR HUMAN THIOREDOXIN IN HUMAN SERUM

Adult T-cell leukemia (ATL)-derived factor (ADF), originally defined a s an inducer of interleukin-2 receptor/alpha-chain (IL-2R/p55) of huma n T-lymphotropic virus type I (HTLV-I) positive T cells, is a human ho mologue of redox-active coenzyme thioredoxin (Trx) of Escherichia coli . In this study, an enzymatic assay system based on the dithiol-depend ent insulin-reducing activity of ADF/Trx was established (insulin-redu cing assay) to determine the amount of ADF/Trx in human serum using NA DPH and Trx reductase purified from human placenta. Insulin-reducing a ctivity was detected in all of the serum samples from healthy voluntee rs (n = 30) screened by this assay, with a mean +/- SD of 10.9 +/- 2.4 U/l. This mean value corresponds with the concentration of 223 ng rec ombinant ADF/Trx (rADF/Trx)/ml. Human serum is known to contain severa l redox-active proteins with ADF/Trx motifs. To differentiate the cont ribution of these proteins and ADF/Trx to the insulin-reducing activit y, the anti-rADF/Trx monoclonal antibody (mAb)-conjugated affinity col umn-depleted sera obtained from an identical source was used for analy sis. The affinity column-depleted sera demonstrated a loss of over 99% of the original activity, white control column depleted sera lost les s than 4%. Furthermore, the amount of affinity-purified ADF/Trx molecu les eluted from the same column almost corresponded with the amount es timated by the insulin-reducing activity. These results showed the pre sence of