The Mechanism Of γδT Cell Activation Via Interaction Between MICA And NKG2D

NKG2D belongs to C-type lectin like immonoreceptor family which widely distribute on the surface of most NK cells, CD8~+αβ T cells and γδ T cells. MHC class I chain-related molecules A (MICA) is one of the ligands for human NKG2D, which is stressfully expressed in most epithelial tumours or pathogen-infected tissue cells. Soluble MICA release of these tumor cells probabally is one of the major reasons that they can successfully escape from immune surveillance. MICA engagement of NKG2D can directly trigger the activation of NK cells and plays co-stimulating roles in the activation of CD8~+ αβ T cells. In terms of γδ T cell activation via NKG2D pathway, however, there are still some disputes. In human, γδ T cells comprise two major subsets- Vy9/82 T cells and Vδ1 T cells, the former represent the majority of γδ T cells in peripherial blood, while the latter predominate in mucosal tissue including the intestinal epithelia. Vγ9/52 TCR recognizes low molecular weight, phosphate-containing nonpeptide antigens whereas V81 TCR recognizes "stress-induced" molecules, such as MICA/MICB.To study the mechanism of NKG2D pathway in cytolytic activity of Vγ9/52 T cells and Vδ1 T cells, we performed the investigations as follows. (1)we successfully cloned cDNA of human NKG2D gene from PBMC, expressed and purified recombinant extracellular segments (80~216aa) of NKG2D protein utilizing pET prokaryotic expressing system; (2)we prepared monoclonal antibody (McAb) of anti-NKG2D with hybridoma technique; (3)with immobilized anti-pan-γδ TCR and rMICA protein, respectively, we expanded predominant Vγ9/82 T cells and V81 T cells from human PBMC and TIL, respectively; (4)we compared the cytotoxicity of Vγ9/82 T cells and Vδ1 T cells to Daudi, HCT-116 and HT-29 tumor cell lines after blocked by...