RESUMEN
The CD94/NKG2 receptors expressed by subpopulations of NK cells and T cells have been implicated as receptors for a broad range of both classical and nonclassical HLA class I molecules. To examine the ligand specificity of CD94/NKG2 proteins, a soluble heterodimeric form of the receptor was produced and used in direct binding studies with cells expressing defined HLA class I/peptide complexes. We confirm that CD94/NKG2A specifically interacts with HLA-E and demonstrate that this interaction is dependent on the association of HLA-E with peptide. Moreover, no interaction between CD94/NKG2A and classical HLA class I molecules was observed, as assayed by direct binding of the soluble receptor or by functional assays using CD94/NKG2A+ NK cells. The role of the peptide associated with HLA-E in the interaction between HLA-E and CD94/NKG2A was also assessed. All class I leader sequence peptides tested bound to HLA-E and were recognized by CD94/NKG2A. However, amino acid variations in class I leader sequences affected the stability of HLA-E. Additionally, not all HLA-E/peptide complexes examined were recognized by CD94/NKG2A. Thus CD94/NKG2A recognition of HLA-E is controlled by peptide at two levels; first, peptide must stabilize HLA-E and promote cell surface expression, and second, the HLA-E/peptide complex must form the ligand for CD94/NKG2A.
Asunto(s)
Antígenos CD/metabolismo , Antígenos HLA/metabolismo , Antígenos de Histocompatibilidad Clase I/metabolismo , Células Asesinas Naturales/inmunología , Células Asesinas Naturales/metabolismo , Lectinas Tipo C , Glicoproteínas de Membrana/metabolismo , Animales , Antígenos CD/genética , Antígenos CD/fisiología , Secuencia de Bases , Línea Celular , Pruebas Inmunológicas de Citotoxicidad , Citotoxicidad Inmunológica , Dimerización , Humanos , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/fisiología , Ratones , Datos de Secuencia Molecular , Subfamília D de Receptores Similares a Lectina de las Células NK , Fragmentos de Péptidos/inmunología , Fragmentos de Péptidos/metabolismo , Unión Proteica/inmunología , Señales de Clasificación de Proteína/inmunología , Señales de Clasificación de Proteína/metabolismo , Solubilidad , Treonina/metabolismo , Transfección/inmunología , Células Tumorales Cultivadas , Antígenos HLA-ERESUMEN
CD94 is a C-type lectin expressed by natural killer (NK) cells and a subset of T cells. Blocking studies using anti-CD94 mAbs have suggested that it is a receptor for human leukocyte antigen class I molecules. CD94 has recently been shown to be a 26-kD protein covalently associated with an unidentified 43-kD protein(s). This report shows that NKG2A, a 43-kD protein, is covalently associated with CD94 on the surface of NK cells. Cell surface expression of NKG2A is dependent on the association with CD94 as glycosylation patterns characteristic of mature proteins are found only in NKG2A that is associated with CD94. Analysis of NK cell clones showed that NKG2A was expressed in all NK cell clones whose CD16-dependent killing was inhibited by cross-linking CD94. The induction of an inhibitory signal is consistent with the presence of two immunoreceptor tyrosine-based inhibitory motifs (V/LXYXXL) on the cytoplasmic domain of NKG2A. Similar motifs are found on Ly49 and killer cell inhibitory receptors, which also transmit negative signals to NK cells.