N-linked glycans in the CD4-binding domain of human immunodeficiency virus type 1 envelope glycoprotein gp160 are essential for the in vivo priming of T cells recognizing an epitope located in their vicinity.

Deglycosylation of viral glycoproteins has been suggested to influence the number of available T cell determinants and to increase T cell recognition of antigens. In this study, we have investigated whether T cell responses to the HIV-1 envelope glycoprotein gp160 were influenced by deletion of three N-glycans of the protein. Wild type (wt) and a mutated form of gp160 (gp160A123) lacking the three N-glycans in the C-terminal CD4-binding region efficiently induced antigen-specific T cell responses in mice of the H-2b, H-2d, and H-2k haplotypes. Further, T cells primed by either wt gp160 or gp160A123 were stimulated in vitro to a similar extent by the homologous and heterologous protein, indicating that deletion of the glycans did not affect the overall immunogenicity and antigenicity of gp160A123. Wild-type gp160 and gp160A123 induced comparable T cell responses to those of epitopes which with respect to the secondary structure of gp160 were distant from the deleted glycans. However, in mice of the H-2b haplotype, wt gp160 primed T cells which responded in vitro to a peptide containing one of the deleted N-glycosylation sites (Asn448), whereas T cells induced by gp160A123 were unable to recognize this peptide. Thus, deletion of the glycans abrogated the in vivo priming of T cells recognizing an epitope in close proximity to the deletion sites. Furthermore, enzymatically deglycosylated gp160 failed to induce a T cell response to this epitope. These results indicate that the in vivo generation of certain T cell determinants from glycoproteins is dependent on the glycosylation of the protein.