Interferon-stimulated gene 15 (ISG15), a ubiquitin-like protein and an amplifier of inflammation, can be induced by interferon (IFN) (9), viral and bacterial infections (10, 11), or certain genotoxic stressors (12), indicating that the expression of ISG15 represents a host response to pathogenic insults. This evidence concerns the gene ISG15 and bacterial infectious disease.