KLRK1 and central nervous system cancer: Soluble lactate metabolic enzyme LDH5 secreted by glioma cells induced tumor infiltrating myeloid cells and circulating monocytes to release the ligand of NK group 2 member D (NKG2D), a surface receptor on NK cells in a long term, leading to the down-regulation of NKG2D and malfunction of tumor lysis (Crane et al., 2014; Figure 3E).