Disclosed is a newly identified B7 family member, zB7H6, which functions as a counter-receptor for the NK cell triggering receptor, NKp30. Methods and compositions for modulating NKp30-mediated NK cell activity based on the interaction of zB7H6 with NKp30, as well as related screening methods, are also disclosed. Further disclosed are anti-zB7H6 antibodies as well as antibody-drug conjugates comprising an anti-zB7H6 antibody conjugated to a therapeutic agent, including methods for using such antibodies and antibody-drug conjugates to exert therapeutic effects against zB7H6-expressing cells.