Differential antibody responsiveness to p19 Gag results in serological discrimination between human T lymphotropic virus type I and type II

A new algorithm based upon the differential antibody responses to two gag gene products (p19 and p24) of human T lymphotropic virus (HTLV) has been suggested for serologic discrimination of HTLV type I (HTLV‐I) and type II (HTLV‐II) [Lillihoj et al., 1990]. To evaluate the practical usefulness of this algorithm, serum specimens from HTLV‐seropositive individuals whose infection was confirmed by PCR analysis to be HTLV‐I (n = 60) or HTLV‐II (n = 61) were analyzed by western blot. The intensities of the antibody response to p24gagand p19gag were scored by one individual without prior knowledge of PCR results. According to the algorithm, specimens with p19 > p24 were classified as HTLV‐I, whereas specimens with p19 < p24 were classified as HTLV‐II. Of 60 PCR confirmed HTLV‐I specimens, 56 had p19 > p24 (93%) while 4 had p19 < p24. Of 61 PCR confirmed HTLV‐II specimens, 56 had p19< p24 (92%) and 5 had p19 > p24. The overall accuracy of serologic differentiation when using this algorithm was 92%, as 4 of 60 HTLV‐I (7%) and 5 of 61 HTLV‐II (8%) could have been wrongly classified. Although the differential antibody response to p19gag and p2 4gag provides a simple means of serologically distinguishing between HTLV‐I and HTLV‐II infection in population‐based epidemiological studies, in a clinical context more accurate means of confirmation are required. The dominant p19gag responses were mapped to the C‐terminus of p19 (p19102–117) Competitive inhibition of p19gag response by peptide p19102–107, however, did not abrogate the binding of serum specimens from HTLV‐I‐infected individuals.