HIV-1 gp140 epitope recognition is influenced by immunoglobulin DH gene segment sequence

Complementarity Determining Region 3 of the immunoglobulin (Ig) H chain (CDR-H3) lies at the center of the antigen-binding site where it often plays a decisive role in antigen recognition and binding. Amino acids encoded by the diversity (D-H) gene segment are the main component of CDR-H3. Each D-H has the potential to rearrange into one of six D-H reading frames (RFs), each of which exhibits a characteristic amino acid hydrophobicity signature that has been conserved among jawed vertebrates by natural selection. A preference for use of RF1 promotes the incorporation of tyrosine into CDR-H3 while suppressing the inclusion of hydrophobic or charged amino acids. To test the hypothesis that these evolutionary constraints on D-H sequence influence epitope recognition, we used mice with a single D-H that has been altered to preferentially use RF2 or inverted RF1. B cells in these mice produce a CDR-H3 repertoire that is enriched for valine or arginine in place of tyrosine. We serially immunized this panel of mice with gp140 from HIV-1 JR-FL isolate and then used enzyme-linked immunosorbent assay (ELISA) or peptide microarray to assess antibody binding to key or overlapping HIV-1 envelope epitopes. By ELISA, serum reactivity to key epitopes varied by D-H sequence. By microarray, sera with Ig CDR-H3s enriched for arginine bound to linear peptides with a greater range of hydrophobicity but had a lower intensity of binding than sera containing Ig CDR-H3s enriched for tyrosine or valine. We conclude that patterns of epitope recognition and binding can be heavily influenced by D-H germ line sequence. This may help explain why antibodies in HIV-infected patients must undergo extensive somatic mutation in order to bind to specific viral epitopes and achieve neutralization.