The invention is directed to purified and isolated novel ULBP polypeptides, the nucleic acids encoding such polypeptides, processes for production of recombinant forms of such polypeptides, antibodies generated against these polypeptides, fragmented peptides derived from these polypeptides, and the uses of the above. ULBP polypeptide can be found on the surface of human B cell lymphomas. Mammalian forms of ULBP polypeptide in isolated or purified forms are provided. In addition, isolated nucleic acids encoding ULBP polypeptides and expression vectors comprising a cDNA encoding ULBP polypeptides are provided. The ULBP polypeptides can be isolated or synthesized and used to prepare antibodies, and in particular monoclonal antibodies, against the polypeptides. The antibodies, in turn, are useful for detecting the presence of ULBP polypeptides in human cell samples, which can be correlated with the existence of a malignant condition in a patient. ULBP polypeptides stimulate IFN-.gamma. production, NK cell proliferation, and CTL activity.