A monoclonal antibody specific to Nap was prepared by using a crude membrane fraction from a cell line which has a high affinity to Nef as an antigen. A cDNA clone which encodes Nap was obtained by screening a cDNA library of said cell line utilizing the specific antibody. The nucleotide sequence of this cDNA was elucidated whereupon the full amino acid sequences of human Nap was identified. Since the anti-Nap monoclonal antibody inhibits the binding of Nef to Nap, it can be used as a new therapeutic agent for AIDS. In addition, it can be applied for the diagnosis of AIDS by clarifying the relation between the expression of Nap and the development of AIDS. Nap can be utilized for binding experiments to Nef. It is useful for the development of novel therapeutic agents for AIDS based upon a mechanism of action which inhibits the attachment of both factors and development of new inhibitors against the onset of AIDS by a mechanism of action different from that of reverse transcriptase inhibitors or protease inhibitors.