RESUMEN
T lymphocytes are activated upon binding of their Ag receptors to a complex of Ag-derived peptides and MHC class I or class II molecules expressed on the surface of APC. It is now well established that APC degrade exogenous Ag in acidic endosomal compartments, and that Ag fragments bind to class II molecules moving through these compartments on their way to the surface of the APC. Although peptides derived from some endogenous Ag can also bind to class II molecules and subsequently be recognized by class II-restricted T cells, the intracellular trafficking pathways that enable endogenous proteins to be processed for association with class II molecules remain controversial. We have analyzed the mechanism by which the envelope (env) protein of the HIV-1 is processed in infected cells for recognition by class II-restricted T cells. A large number of env-specific class II-restricted human CTL clones were shown to lyse B-lymphoblastoid cell lines expressing the env. A novel dilutional assay proved that A novel dilutional assay proved that recognition of endogenous env protein was not a consequence of release and re-uptake of the env protein and subsequent processing by the standard class II-restricted pathway. Processing of endogenous env protein required that the protein be co-translationally translocated into the endoplasmic reticulum (ER) and then exit the ER, since the class II-restricted CTL did not recognize env protein localized to the cytosol or retained in the ER of target cells. Under these conditions, however, class I-restricted recognition was readily demonstrated. Finally, class II-restricted recognition was strikingly dependent upon the steady state level of surface env protein, since extracellular reagents that removed intact env protein from the surface of target cells inhibited recognition. This inhibition operated at the Ag-processing level rather than at the level of subsequent Ag recognition. These results provide the first direct evidence that endogenously synthesized membrane proteins enter the class II-restricted Ag-processing pathway after expression on the cell surface in an intact form.
Asunto(s)
Proteína gp120 de Envoltorio del VIH/metabolismo , Proteína gp41 de Envoltorio del VIH/metabolismo , Infecciones por VIH/inmunología , Linfocitos T/inmunología , Células Presentadoras de Antígenos/inmunología , Antígenos de Superficie/inmunología , Secuencia de Bases , Antígenos CD4/química , Antígenos CD4/metabolismo , Membrana Celular/inmunología , Membrana Celular/metabolismo , Células Cultivadas , Retículo Endoplásmico/inmunología , Proteína gp120 de Envoltorio del VIH/inmunología , Proteína gp41 de Envoltorio del VIH/inmunología , Antígenos HLA-D/inmunología , Antígenos de Histocompatibilidad Clase I/inmunología , Técnicas In Vitro , Datos de Secuencia Molecular , Oligodesoxirribonucleótidos/química , SolubilidadRESUMEN
Both CD4+ and CD8+ CTL responses specific for the HIV-1 envelope proteins can be elicited in seronegative humans by candidate AIDS vaccines. The phenotype of the responding CTL depends upon the nature of the vaccine, with CD8+ CTL being found exclusively in recipients of live virus vaccines. Both types of CTL are active against HIV-1-infected cells in vitro. However, the potential efficacy of vaccine-induced CTL in preventing infection in vaccinated individuals exposed to HIV-1 is unknown and is likely to be dependent upon complex factors including lytic activity against divergent strains, cytokines produced, and the lysis of noninfected CD4+ T cells.
Asunto(s)
Vacunas contra el SIDA/inmunología , Productos del Gen env/inmunología , Antígenos VIH/inmunología , Seropositividad para VIH/inmunología , VIH-1/inmunología , Subgrupos de Linfocitos T/inmunología , Vacunas Sintéticas/inmunología , Linfocitos T CD4-Positivos/inmunología , Células Clonales/inmunología , Productos del Gen env/administración & dosificación , Antígenos VIH/administración & dosificación , Proteína gp120 de Envoltorio del VIH/inmunología , Proteínas gp160 de Envoltorio del VIH , Antígenos HLA-D/inmunología , Humanos , Inmunidad Celular , Activación de Linfocitos , Precursores de Proteínas/inmunología , Vacunas Atenuadas/inmunologíaRESUMEN
The propensity of HIV-1 to undergo sequence variation, particularly in the envelope glycoprotein gp120, complicates vaccine development and may enable the virus to evade ongoing immune responses in infected individuals. We present here a molecular analysis of the effects of this variability on human T cell recognition of HIV-1 gp120. Synthetic peptides representing a defined CD4+ human T cell epitope in gp120 were used to survey gp120 molecules from various HIV-1 strains for the capacity to be recognized in the context of a single human MHC molecule, DR4. Variation affected recognition at two levels. For some strains, variation in this epitope was sufficient to alter the interaction of Ag receptors on gp120-specific human T cell clones with peptide-DR4 complexes on APC. In the case of two strains, the natural variation was sufficient to prevent the critical initial interaction between the relevant gp120 peptides and DR4 on the APC. However, these strains were highly divergent from the reference strain. Thus it is encouraging to note that the range of natural sequence variation in this T cell epitope falls, for the most part, within the range of peptide sequences that can be accommodated by the relevant human MHC molecule.