Compositions and methods for regulating an immune response in a subject are described. More particularly, described are human antibodies that regulate the activity of NK cells and allow a potentiation of NK cell cytotoxicity in mammalian subjects, and antibodies having antigen-binding properties similar to those of human monoclonal antibody 1-7F9 or 1-4F1. Described also are also fragments and derivatives of such antibodies, as well as pharmaceutical compositions comprising the same and their uses, particularly for use in therapy, to increase NK cell activity or cytotoxicity in subjects.