Oligopeptide having proinflammatory cytokine secretion-inhibiting activity

An oligopeptide having inhibitory activity on proinflammatory cytokine secretion from cells, the oligopeptide containing a DE loop sequence of RANKL protein, a β-strand D sequence of RANKL protein adjacent to the N-terminal side of the DE loop sequence, and a β-strand E sequence of RANKL protein adjacent to the C-terminal side of the DE loop sequence,

• wherein the oligopeptide is free of a CD loop sequence of RANKL protein, the DE loop sequence has the amino acid sequence of SEQ ID NO:
• 1, the β-strand D sequence has the amino acid sequence of any one of SEQ ID NOs:
• 2 to 5, the β-strand E sequence has the amino acid sequence of any one of SEQ ID NOs:
• 6 to 9, and the length of the oligopeptide is no more than 50 amino acid residues.