Cynomolgus Monkey (Macaca fascicularis) Interleukin-8 (IL-8), also known as CXCL8, is a potent pro-inflammatory chemokine that plays a central role in innate immune responses by mediating neutrophil chemotaxis, activation, and migration to sites of infection or tissue injury. Structurally and functionally highly homologous to human IL-8, cynomolgus IL-8 signals through CXCR1 and CXCR2 receptors to activate downstream pathways that drive neutrophil recruitment, degranulation, and amplification of inflammatory cascades. IL-8 is rapidly induced in response to viral, bacterial, and inflammatory stimuli and is elevated in nonhuman primate models of diseases such as dengue, influenza, SARS-CoV-2, tuberculosis, and bacterial sepsis, where its expression correlates with disease severity and pulmonary or systemic inflammation. Due to the close genetic and immunological similarity of cynomolgus monkeys to humans, IL-8 is widely used as a biomarker of immune activation in preclinical vaccine studies, infectious disease models, toxicology assessments, and evaluation of biologics targeting inflammatory pathways. Characterization of cynomolgus IL-8 is therefore critical for translational research into neutrophil-driven pathology, cytokine and chemokine network dynamics, and therapeutic modulation of inflammatory responses relevant to human infectious, autoimmune, and inflammatory diseases.