HIGH-LEVEL PRODUCTION OF ALTERNATIVELY SPLICED SOLUBLE INTERLEUKIN-6 RECEPTOR IN SERUM OF PATIENTS WITH ADULT T-CELL LEUKEMIA HTLV-I-ASSOCIATED MYELOPATHY

We have previously shown, using human T-cell lymphocytotrophic virus-1 (HTLV-1)-infected cell lines, that soluble Interleukin-6 receptor (sI L-6R) is generated through an alternative splicing mechanism. In this study, we examined human sera for the presence of alternatively splice d soluble IL-6R (AS-sIL-6R). We produced a monoclonal antibody (mAb) r ecognizing the unique sequence of AS-sIL-6R peptide, generated by an a ltered reading frame. We also made recombinant AS-sIL-6R protein in Sp ordoptera frugiperda-9 (Sf-9) cells carrying baculovirus, which encode d altered sIL-6R or conventional IL-6R cDNA. mAbs specifically recogni zed AS-sIL-6R, but not conventional IL-6R, as demonstrated by Western blot analyses, fluorescence-activated cell sorter, immunofluorescence analyses and enzyme-linked immunosorbent assay (ELISA). We adapted an ELISA system and used it for detection of altered sIL-6R in sera from 23 healthy persons, 12 patients with adult T-cell leukaemia (ATL) and 13 patients with HTLV-1-associated myelopathy (RAM). Serum levels of A S-sIL-6R were 6.4 or 6.1 times greater in ATL (28.7 +/- 20.4 ng/ml, P < 0.0001) and in HAM patients (27.5 +/- 12.1 ng/ml, P < 0.0001) than i n healthy individuals (45 +/- 2.1 ng/ml). High levels of AS-sIL-6R wer e also observed in plasma from rheumatoid arthritis patients and in pe rsons with elevated levels of alanine aminotransferase (ALT), antinucl ear antibody (ANA), or alpha-fetoprotein (AFP). However, in human immu nodeficiency virus-1 (HIV-1), hepatitis B virus (HBV) or hepatitis C v irus (HCV)-infected individuals, AS-sIL-6R levels were not elevated. I n this study, we confirmed that AS-sIL-6R is indeed present in human s era. These observations suggest that alternative splicing of IL-6R mRN A is of consequence in ATL, HAM and in some autoimmune diseases. The H TLV-1-infected T cells appeared to play an important role in AS-sIL-6R production.