HRK (Harakiri, derived from the Japanese term for "ritual suicide") antibody is a tool used to study the HRK protein, a pro-apoptotic member of the BCL-2 protein family. Discovered in 1997. HRK interacts with anti-apoptotic proteins like BCL-2 and BCL-XL through its BH3 domain, triggering mitochondrial outer membrane permeabilization (MOMP) and caspase activation. Its expression is primarily observed in neurons and hematopoietic cells, where it regulates programmed cell death under stress conditions. HRK antibodies enable detection of endogenous HRK levels in research models, aiding investigations into apoptosis mechanisms and disease pathogenesis. Studies link HRK dysregulation to neurodegenerative disorders (e.g., Alzheimer's) and cancers, where its downregulation often correlates with chemoresistance. However, HRK's low basal expression in healthy tissues and complex epigenetic regulation pose challenges for detection, requiring optimized antibody validation. Current research focuses on HRK's role in balancing cell survival/death decisions and its potential as a therapeutic target. These antibodies are crucial for elucidating HRK's tissue-specific functions and its interplay with other BCL-2 family proteins in health and disease.