Serotyping of HIV Type 1 Infections: Definition, Relationship to Viral Genetic Subtypes, and Assay Evaluation

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Abstract
V3 serotyping refers to a system based on binding of antibody in patient sera to V3-loop peptides derived from HIV-1 env genetic subtypes. The V3X serotype represents reactivity of serum from an HIV-1-infected patient (regardless of viral genetic subtype), which reacts preferentially to a V3 peptide derived from the X subtype sequence. We have classified HIV-1 serotypes, determined the relationship between the HIV-1 V3 serotypes and viral genetic subtypes in a large study (n = 125), and evaluated the performance of three different V3 peptide-binding assays. Seven HIV-1 V3 serotypes were identified: A, B, B-Br, B-Th, C, D, and E. Serotypes B-Br and B-Th represent sera that react specifically to peptides derived from Brazilian B (B-Br, GWGR) and Thai B (B-Th, GPGQ) strains. The HIV-1 V3 B, C, and E serotypes correlated closely with their viral env genetic subtypes; 19–26 of 32 B sera (59–79%), 3–4 of 4 C sera (75–100%), and 19–22 of 23 E sera (83–96%) were identified as serotypes B, C, and E, respectively. In contrast, two major V3 serotypes were classified in A sera: A (14–18 of 36 [40–50%]) and C (12–19 of 36 [33–54%]). Similarly, two major V3 serotypes were classified in D sera: B (6–10 of 20 [30–50%]) and D (9–12 of 20 [45–60%]). Serotyping of subtype E sera showed the best concordance with genetic subtypes by all assays. Overall, HIV-1 V3 serotyping produced consistent results among three laboratories. However, HIV-1 V3 serotypes do not distinguish all HIV-1 genetic subtypes. The relative biological significance of the V3 serotypes remains to be elucidated.
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