Evaluation of Enzyme Immunoassay using a Recombinant Envelope Protein Expressed in Insect Cells for Serological Confirmation of HTLV-I Infection

A recombinant human T-lymphotropic virus type I (HTLV-I) envelope protein expressed in insect cells using a recombinant baculovirus was employed as the antigen in an enzyme immunoassay (renvEIA). Peripheral blood samples were obtained from asymptomatic carriers or healthy individuals. Plasma was tested for HTLV-I antibody by renvEIA, particle agglutination, and Western immunoblot (WB), and lymphocyte DNA was tested for HTLV-I proviral DNA amplification by polymerase chain reaction (PCR). Of 61 people aged 9 months or older, 23 were positive (gag+, env+) and 19 others were in the “indeterminate” category (gag+, env-) when their WB results were interpreted according to the WHO-proposed criteria. Thirty-seven cases, including all of the WB⁺ cases and 14 of 19 WB indeterminate cases, were positive by renvEIA. In 34 of 37 renvEIA-positive cases, the presence of long terminal repeat (LTR) and tax/rex region of HTLV-I proviral DNA was detected by polymerase chain reaction (PCR) and following Southern blot hybridization. Thus, renvEIA would be a useful supplemental assay to confirm the presence of HTLV-I antibody in HTLV-I asymptomatic carriers.