Immune response in infection: Role of human NKG2H receptor and study of HLA-­E restricted lymphocytes

Resumen

The NKG2 family is one of the multiple families of immune receptors encoded in the human genome that contains members with activating and inhibitory potential. The CD94/NKG2A inhibiting and CD94/ NKG2C activating receptors are mainly expressed on NK cells and subsets of CD8+ T cells and have been shown to play an important role in regulating immune responses against infected and tumour cells. However the biology of other members of the NKG2 family has been much less explored. Strikingly, both CD94/NKG2A and CD94/NKG2C can bind the same ligand; the non-classical HLA class I molecule HLA-E loaded with nonamer peptides derived from the signal sequence of classical MHC class I molecules or with peptides derived from other proteins, including pathogen proteins, to form peptide/HLA-E/¿2-microglobulin trimers that can be recognized by specific T cells for immune activation. The experiments described in this thesis have addressed two aspects of the biology of the CD94/NKG2 ¿ HLA-E system: In the first part of this work, the NKG2H receptor, an as yet poorly characterized member of the NKG2 family has been studied in detail. NKG2H was expressed on low numbers of peripheral blood lymphocytes, mainly on CD3+CD56+ and CD3+CD8+ T cells. Activation of NKG2H expressing cells markedly reduced the activation and proliferation of the other T cells in the culture via induction of apoptosis. This suppressive activity was characteristic of NKG2H but not for NKG2A or NKG2C expressing cells and did not depend on the release of soluble factors or recognition of MHC class I molecules. A marked increase in the proportion of T and NK cells expressing NKG2H+ but not NKG2A+ or NKG2C+ cells was observed after co-culture of PBMCs, from healthy HCMV seronegative individuals, with HCMV infected fibroblasts. The expansion of NKG2H+ cells depended on contact between PBMCs and HCMV infected fibroblasts and separation of these cells led to the loss of NKG2H expression. In the second part of the thesis, a possible role of Mycobacterium tuberculosis (Mtb) ¿ peptide specific, HLA-E restricted cells in the immune response of bladder cancer patients receiving BCG immunotherapy was studied. Low frequencies of CD8+ T cells reactive with the Mtb-peptide/HLA-E tetramers were observed in the peripheral blood of these patients. Our data are the first to describe the populations of cells that express the CD94/NKG2H receptor, the effects on lymphocyte function elicited by receptor ligation and a possible role for CD94/NKG2H in immune responses to viral infection. Further, the HLA-E tetramer staining method has been shown to be applicable for the detection and characterization of Mtb specific HLA-E restricted T cells during BCG therapy in bladder cancer patients, although this approach could be improved by use of a larger library of Mtb-peptide/HLA-E complexes.