CTSB (Cathepsin B) is a lysosomal cysteine protease involved in proteolysis, protease activity enhancement, neurogenesis and memory function. CTSB is present in the perinuclear lysosomes of normal epithelial cells and non-malignant tumors. It is also found on the membranes of tumor cells including gliomas and oral squamous cell carcinomas, and it can be upregulated in cancer. Elevated levels of CTSB can result in inflammation and increased cell death and are correlated with seizures, memory loss and other neurodegenerative effects in brain injury and neurological diseases. Furthermore, CTSB is a marker of the dedifferentiated chondrocyte phenotype and contributes to cartilage destruction in osteoarthritis and pathological proteolysis in rheumatoid arthritis and cancer. In immunohistochemistry, CTSB has cytoplasmic positivity in all tissues. References: The Journal of Biological Chemistry. 285 (3): 2120–9, PMID: 19858192; PLoS One. 11 (3): e0152165, PMID: 27031837; Stem Cell Research. 12 (3): 716–29, PMID: 24699410; Cell Metabolism. 24 (2): 332–40, PMID: 27345423; Journal of Neuroscience Research. 88 (13): 2847–58, PMID: 20653046; Journal of Neurobiology. 56 (4): 315–27, PMID: 12918016.