Human immunodeficiency virus type 1 (HIV-1) entry is mediated by the interaction between a variably glycosylated envelope glycoprotein (gp120) and host-cell receptors. Approximately half of the molecular mass of gp120 is contributed by N-glycans, which serve as potential epitopes and may shield gp120 from immune recognition. The role of gp120 glycans in the host immune response to HIV-1 has not been comprehensively studied at the molecular level. We developed a new approach to characterize cell-specific gp120 glycosylation, the regulation of glycosylation, and the effect of variable glycosylation on antibody reactivity. A model oligomeric gp120 was expressed in different cell types, including cell lines that represent host-infected cells or cells used to produce gp120 for vaccination purposes. N-Glycosylation of gp120 varied, depending on the cell type used for its expression and the metabolic manipulation during expression. The resultant glycosylation included changes in the ratio of high-mannose to complex N-glycans, terminal decoration, and branching. Differential glycosylation of gp120 affected envelope recognition by polyclonal antibodies from the sera of HIV-1-infected subjects. These results indicate that gp120 glycans contribute to antibody reactivity and should be considered in HIV-1 vaccine design.

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BackgroundHIV-1 entry into host cells is mediated by interactions between the virus envelope glycoprotein (gp120/gp41) and host-cell receptors. N-glycans represent approximately 50% of the molecular mass of gp120 and serve as potential antigenic determinants and/or as a shield against immune recognition. We previously reported that N-glycosylation of recombinant gp120 varied, depending on the producer cells, and the glycosylation variability affected gp120 recognition by serum antibodies from persons infected with HIV-1 subtype B. However, the impact of gp120 differential glycosylation on recognition by broadly neutralizing monoclonal antibodies or by polyclonal antibodies of individuals infected with other HIV-1 subtypes is unknown.MethodsRecombinant multimerizing gp120 antigens were expressed in different cells, HEK 293T, T-cell, rhabdomyosarcoma, hepatocellular carcinoma, and Chinese hamster ovary cell lines. Binding of broadly neutralizing monoclonal antibodies and polyclonal antibodies from sera of subtype A/C HIV-1-infected subjects with individual gp120 glycoforms was assessed by ELISA. In addition, immunodetection was performed using Western and dot blot assays. Recombinant gp120 glycoforms were tested for inhibition of infection of reporter cells by SF162 and YU.2 Env-pseudotyped R5 viruses.ResultsWe demonstrated, using ELISA, that gp120 glycans sterically adjacent to the V3 loop only moderately contribute to differential recognition of a short apex motif GPGRA and GPGR by monoclonal antibodies F425 B4e8 and 447-52D, respectively. The binding of antibodies recognizing longer peptide motifs overlapping with GPGR epitope (268 D4, 257 D4, 19b) was significantly altered. Recognition of gp120 glycoforms by monoclonal antibodies specific for other than V3-loop epitopes was significantly affected by cell types used for gp120 expression. These epitopes included CD4-binding site (VRC03, VRC01, b12), discontinuous epitope involving V1/V2 loop with the associated glycans (PG9, PG16), and an epitope including V3-base-, N332 oligomannose-, and surrounding glycans-containing epitope (PGT 121). Moreover, the different gp120 glycoforms variably inhibited HIV-1 infection of reporter cells.ConclusionOur data support the hypothesis that the glycosylation machinery of different cells shapes gp120 glycosylation and, consequently, impacts envelope recognition by specific antibodies as well as the interaction of HIV-1 gp120 with cellular receptors. These findings underscore the importance of selection of appropriately glycosylated HIV-1 envelope as a vaccine antigen.

IgA nephropathy (IgAN) is the dominant type of primary glomerulonephritis worldwide. However, IgAN rarely affects African Blacks and is uncommon in African Americans. Polymeric IgA1 with galactose-deficient hinge-region glycans is recognized as auto-antigen by glycan-specific antibodies, leading to formation of circulating immune complexes with nephritogenic consequences. Because human B cells infected in vitro with Epstein-Barr virus (EBV) secrete galactose-deficient IgA1, we examined peripheral blood B cells from adult IgAN patients, and relevant controls, for the presence of EBV and their phenotypic markers. We found that IgAN patients had more lymphoblasts/plasmablasts that were surface-positive for IgA, infected with EBV, and displayed increased expression of homing receptors for targeting the upper respiratory tract. Upon polyclonal stimulation, these cells produced more galactose-deficient IgA1 than did cells from healthy controls. Unexpectedly, in healthy African Americans, EBV was detected preferentially in surface IgM-and IgD-positive cells. Importantly, most African Blacks and African Americans acquire EBV within 2 years of birth. At that time, the IgA system is naturally deficient, manifested as low serum IgA levels and few IgA-producing cells. Consequently, EBV infects cells secreting immunoglobulins other than IgA. Our novel data implicate Epstein-Barr virus infected IgA + cells as the source of galactose-deficient IgA1 and basis for expression of relevant homing receptors. Moreover, the temporal sequence of racial-specific differences in Epstein-Barr virus infection as related to the naturally delayed maturation of the IgA system explains the racial disparity in the prevalence of IgAN.