To provide a relatively low-molecular peptide usable in screening diagnostics or therapeutic agents for various diseases caused by the abnormal activation of macrophage or microglia.

The subject method is characterized by comprising using a compound of the general formula (1):R1-Leu(or Ile)-His-Thr-Leu-R2 [wherein, R1 is a (modifying group-bearing) amino acid residue, (modifying group-bearing) peptide residue, amino acid N-terminal protective group or H atom; R2 is a (modifying group-bearing) amino acid residue, (modifying group-bearing) peptide residue, amino acid C-terminal protective group or H atom; Leu is a leucine residue; Ile is an isoleucine residue; His is a histidine residue; and Thr is a threonine residue].