An isolated antibody, comprising: heavy chain complementary determining regions CDR1, CDR2, and CDR3 of a heavy chain variable region sequence selected from SEQ ID NOs: 2, 6, 10, and 14; and light chain complementary determining regions CDR1, CDR2, and CDR3 of a light chain variable region sequence selected from SEQ ID NOs: 4, 8, 12, and 16; wherein the antibody binds specifically to a RSPO3 protein.