This invention provides a first polypeptide comprising all or a portion of the extracellular domain of ILT3, wherein the polypeptide is water-soluble and does not comprise the Fc portion of an immunoglobulin. This invention also provides a second polypeptide comprising (i) all or a portion of the extracellular domain of ILT3 operable affixed to (ii) the Fc portion of an immunoglobulin, wherein the Fc portion of the immunoglobulin comprises a function-enhancing mutation, and wherein the polypeptide is water-soluble. This invention further provides a third polypeptide comprising (i) all or a portion of the extracellular domain of ILT3 operable affixed to (ii) a transmembrane domain. This invention further provides related nucleic acids, expression vectors, host vector systems, compositions, and articles of manufacture and therapeutic and prophylactic methods using the polypeptides of the invention.
