Enables endopeptidase inhibitor activity. Involved in antibacterial humoral response; innate immune response; and response to lipopolysaccharide. Located in extracellular space. Is expressed in embryo; liver left lobe; liver right lobe; and ureter. Orthologous to human SLPI (secretory leukocyte peptidase inhibitor). [provided by Alliance of Genome Resources, Apr 2022]