Higher Western blot immunoreactivity of glycoprotein 120 from R5 HIV type 1 isolates compared with X4 and X4R5 isolates

The envelope glycoprotein of human immunodeficiency virus 1 (HIV-1) plays important roles in viral life cycle and pathogenesis. Understanding the immune responses the protein elicits during the course of a viral infection in patients is important in designing an effective vaccine candidate against the virus or for better diagnosis of the disease. In this study, we report that gp120 of R5 isolates have higher Western blot (WB) immunoreactivity to antibodies elicited against the protein in virus-infected human patients compared with that of X4 and X4R5 isolates. Analyses of WE immunoreactivity of chimeric gp120s constructed between R5 (AD8) and X4R5 (DH12) HIV-1 isolates indicate that there are complex tertiary interdomain interactions even after a complete denaturation of the protein. Our data suggest that the determinant(s) responsible for the high WE immunoreactivity might be present in all gp120s, but are accessible to antibodies only for R5 gp120s in the WE assay. The V1/V2 and/or V3 regions of X4 and X4R5 gp120s likely interfere with either the formation or surface exposure of the WE immunoreactive determinant, Supplementing HIV-1 WE diagnosis kits with purified R5 gp120 could improve their sensitivity and facilitate earlier diagnosis of virus infection.