B7-like polypeptides, proteins, and nucleic acid molecules are disclosed. In addition to isolated, full-length B7-like proteins, the invention further provides isolated B7-like fusion proteins, antigenic peptides, and anti-B7-like antibodies. The invention also provides B7-like nucleic acid molecules, recombinant expression vectors containing a nucleic acid molecule of the invention, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a B7-like gene has been introduced or disrupted. Diagnostic, screening, and therapeutic methods utilizing compositions of the invention are also provided.