Abstract: A recombinant natural killer cell activating factor is disclosed, preferably having a peptide of the following amino acid sequence in its molecule. The invention provides a cDNA coding for a recombinant natural killer cell activating factor, a expression plasmid involving the cDNA, a host transformed with the plasmid, an antitumor agent containing the recombinant natural killer cell activating factor and a pharmaceutical composition which comprises a pharmacologically effective amount of the antitumor agent and a pharmacologically acceptable carrier.

Abstract: A piezo-resonator comprises a supporting frame having a recess for attaching a piezoelectric resonator element. This recess consists of three portions, that is, a central portion, a pair of connecting portions which are outside of the central portion and a pair of end portions which are outside of the pair of connecting portions. The width W.sub.2 of the connecting portion, the width W.sub.1 of the central portion and the width W.sub.3 of the end portion have the relationship W.sub.2 >W.sub.1 >W.sub.3. Two terminals intersect respective connecting portions to be embedded in the supporting frame.