Unusual pattern of antibodies to human T-cell leukemia virus type-I in family members of adult T-cell leukemia patients.

Detection methods for the human T-cell leukemia virus type-I (HTLV-I) for blood screening and diagnosis generally rely on antibody tests that use the structural proteins of HTLV-I as antigen. We have found an unusual pattern of antibody reactivity among people who are at high risk of HTLV infection due to being a family member of an adult T-cell leukemia (ATL) patient: a specific antibody reaction exclusively directed to the HTLV regulatory protein tax, and not to the HTLV-I structural proteins. Sera from 7 of 82 (8.5%) structural antibody-undetectable family members of ATL patients had the anti-tax reactivity. Two seroconverters were observed. One seroconverter a healthy resident of Miyazaki, tested negative for structural antibody, but positive for tax antibody. Two years later she tested positive for both. The other seroconverter, an Israeli hemophiliac, tested negative for both antibodies, but converted to tax antibody-positive/structural antibody-negative. The HTLV-I tax-only antibody profile was also observed in sera sets from two other populations at risk for HTLV infection, human immunodeficiency virus-1-infected patients at the Bronx-Lebanon Hospital in New York and Israeli hemophiliacs. DNA samples from lymphocytes of four individuals with antibody reactivity only to HTLV-I tax were tested in polymerase chain reaction experiments; no HTLV-I or -II DNA was detected.