IL-8
Summary
IL-8 (CXCL8) is a chemokine primarily responsible for neutrophil chemotaxis and activation at sites of acute inflammation. It is released by macrophages, endothelial cells, and epithelial cells in response to infection or tissue injury, forming a concentration gradient that recruits neutrophils to the affected area.
Detail
IL-8 (CXC chemokine ligand 8, CXCL8) belongs to the CXC chemokine family and acts via GPCR receptors CXCR1 and CXCR2 on neutrophils. It is produced by macrophages, epithelial cells, endothelial cells, and fibroblasts in response to pro-inflammatory stimuli such as TNF-α, IL-1, and bacterial products (e.g., LPS). Its primary function is to serve as a potent chemoattractant for neutrophils, guiding them from the bloodstream through endothelium (via upregulation of adhesion molecules) to sites of infection or tissue damage, where they perform phagocytosis and release antimicrobial substances. IL-8 also promotes angiogenesis and plays a role in the pathogenesis of several inflammatory and malignant conditions. Clinically, elevated IL-8 levels are associated with acute bacterial infections, acute respiratory distress syndrome (ARDS), psoriasis, and chronic inflammatory diseases like COPD and inflammatory bowel disease. On USMLE exams, IL-8 is classically tested as 'the neutrophil chemotactic factor'—remember the mnemonic 'clean up on aisle 8' for neutrophil recruitment. It is often compared with other key interleukins: IL-1 and TNF-α (endogenous pyrogens), IL-6 (acute phase response/fever), IL-8 (neutrophil chemotaxis), and IL-12 (Th1 differentiation, NK cell activation).
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Janeway's Immunobiology
- Kaplan USMLE Step 1 Lecture Notes - Immunology
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