PROBLEM TO BE SOLVED: To obtain a new polypeptide containing a specific amino acid sequence and inducing production of interferon-γ in an immunocompetent cell and useful as an agent for sensitive diseases such as antitumor agents, antiviral agents and antibacterial agents. SOLUTION: This new polypeptide contains an amino acid sequence represented by formulas I to III as a partial amino acid sequence. The polypeptide contains an amino acid sequence in which one or more cysteines in the polypeptide are replaced by other amino acid or an amino acid sequence in which one or more amino acids are added, lost or replaced in the part other than the above replaced part in the replaced amino acid sequence and induces production of interferon-γ in an immunocompetent cell and useful as an antitumor agent, an antiviral agent, antibacterial agent, an agent for immunologic diseases. The polypeptide is obtained by cloning a chromosome DNA separated from established cell derived from human acute lymphoblastic leukemia and expressing the resultant gene.