This invention provides an artificially synthesized peptide having an activity to inhibit the expression of type 2 TNF receptor (TNF-R2), and a TNF-R2 expression-inhibiting composition including the peptide as an active ingredient. Also provided is a method for inhibiting the expression of TNF-R2 in cells capable of expressing TNF-R2, by using the peptide. The expression of TNF-R2 in the cells is inhibited, by supplying the cells capable of expressing TNF-R2 with a synthetic peptide essentially including of an amino acid sequence constituting a signal peptide in an amyloid precursor protein (APP) or an amino acid sequence formed by substituting, deleting and/or adding one or several amino acid residues in/from/to the amino acid sequence of the signal peptide.
