CD16 has been identified as Fc receptors Fc?RIIIa (CD16a) and Fc?RIIIb (CD16b). These receptors bind to the Fc portion of IgG antibodies which then activates the NK cell for antibody-dependent cell-mediated cytotoxicity. A lack of CD16 in a given population of neutrophils may indicate prematurity, as could be caused by a left shift due to neutrophilic leukocytosis induced by tissue necrosis or bacterial infection.