Low level of FcγRIII expression on murine natural killer cells.

Cellular Fcγ-receptors are crucial for mediating the functions of therapeutic antibodies. Antibody dependent cellular cytotoxicity (ADCC) is an important mechanism by which Fcγ-receptor expressing cells of the innate immune system including natural killer (NK) cells can kill opsonized target cells. During FACS analysis, however, binding of the Fc-fragment of staining antibodies specific for cell type specific receptors can lead to false positive results and wrong interpretation of the data. Current strategies to block such unwanted binding largely target FcγRIIB and FcγRIII but not the recently identified mouse FcγRIV. In this study we demonstrate that Fc-dependent binding of the NK cell specific antibody NK1.1 by FcγRIV on monocytes results in a large overestimation of FcγRIII expression on murine NK cells. These results highlight the importance of blocking unwanted binding of FACS antibodies to FcγRIV and shed new light on the expression level of FcγRIII on NK cells in mice during the steady state.