Non-classical MHC: HLA-E and Qa-1b
Human leukocyte antigen E (HLA-E) is a non-classical class I molecule recognized by natural killer (NK) cells and CD8+ T cells. HLA-E is expressed in almost all tissues including lung, liver, skin and placental cells.3 HLA-E expression is also detected in solid tumors (e.g., osteosarcoma and melanoma).9 HLA-E binds to TCR expressed on CD8+ T cells, resulting in the T cell activation.6 HLA-E is also known to bind CD94/NKG2 receptor expressed on NK cells and CD8+ T cells.2 CD94 can pair with several different isoforms of NKG2 to form receptors with potential to either inhibit (NKG2A, NKG2B) or promote (NKG2C) cellular activation.
HLA-E preferably binds to a peptide derived from amino acid residues 3-11 of the leader sequences of most HLA-A, -B, -C, and -G molecules, but cannot bind its own leader peptide.2 Under physiological conditions, the engagement of CD94/NKG2A with HLA-E, loaded with peptides from the HLA class I leader sequences, usually induces inhibitory signals. Cytomegalovirus (CMV) utilizes the mechanism for escape from NK cell immune surveillance via expression of the UL40 glycoprotein, mimicking the HLA-A leader3-11.4 However, it is also reported that CD8+ T cells can recognize HLA-E loaded with the UL4015-23 peptide derived from CMV Toledo strain and play a role in defense against CMV.6 A number of studies revealed several important functions of HLA-E in infectious disease and cancer.5,7,8
The HLA-E tetramer is comprised of human class I HLA-E*01:03 and epitope peptide derived from the HLA-A leader, and it can detect HLA-E*01:03-restricted HLA-A leader3-11-specific NK cells and CD8+ T cells by flow cytometry.
The non-classical class I mouse homolog of HLA-E tetramer, Qa-1b tetramer, is now available.
For Research Use Only. Not for use in diagnostic procedures.
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- Pietra G, et al. PNAS 100: 10896-10901 (2003)
- Salerno-Gonçalves R, et al. J Immunol 173: 5852-5862 (2004)
- Derré L, et al. J Immunol 177: 3100-3107 (2006)
- Monaco EL, et al. Neoplasia 13: 822-830 (2011)
- Weder P, et al. Results in Immunology 2: 88-96 (2012)