We found that cytotoxicity of NK cells dramatically decreased during sepsis, likely due to the reduction of cluster of differentiation (CD)3<sup>-</sup> CD56<sup>+</sup> NK cells and a shift of phenotypic changes of NK group 2 member (NKG2) receptors, natural cytotoxicity receptors (NCRs) and killer immunoglobulin-like receptors (KIRs) toward inhibitory receptors demonstrated by CD3<sup>-</sup> CD56<sup>+</sup> NK cells in septic patients.