A therapeutic agent for treating an infectious or inflammatory disease, a pharmaceutical composition for treating an infectious or inflammatory disease, and a method of using a pharmaceutical composition are provided. The pharmaceutical composition includes a peptide ligand that binds with CXCR2 as an active component. The active component can be useful in preventing and treating infectious and/or inflammatory diseases, including sepsis and septic shock by promoting the removal of bacteria by phagocytosis, suppressing an inflammatory response, and suppressing the apoptosis of immune cells.
