S100A9. also known as calgranulin B or MRP14. is a calcium-binding protein belonging to the S100 family. It primarily forms a heterodimer with S100A8 (calgranulin A), collectively termed calprotectin, which plays critical roles in inflammation, immune response, and cellular homeostasis. S100A9 is predominantly expressed in neutrophils, monocytes, and macrophages, and its secretion is upregulated during infection, tissue injury, or chronic inflammatory conditions. The protein interacts with receptors like TLR4 and RAGE, modulating pro-inflammatory signaling pathways, leukocyte recruitment, and antimicrobial activity.
S100A9 antibodies are essential tools for detecting and quantifying this protein in research and diagnostics. They enable the study of S100A9's involvement in diseases such as rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, and cancer, where its overexpression correlates with tumor progression, metastasis, and immune evasion. These antibodies are utilized in techniques like Western blotting, immunohistochemistry, and ELISA to assess protein expression, localization, and function. Some therapeutic applications are also explored, aiming to neutralize S100A9's pathogenic effects in chronic inflammation or cancer. However, challenges remain in ensuring antibody specificity due to structural similarities within the S100 family. Validated S100A9 antibodies are critical for advancing research into its dual roles as a damage-associated molecular pattern (DAMP) molecule and a potential biomarker for inflammatory or malignant disorders.