Triple Point Biologics' Cysteine Proteinase Inhibitors antibody catalog covers seven functionally characterized family members — cystatin A, B, C, D, S, and SA, and calpastatin — produced as rabbit polyclonal antibodies validated for research use in Western blot. Cysteine proteinase inhibitors are endogenous regulators of cysteine proteases, acting primarily through tight-binding, reversible inhibition of papain-superfamily enzymes including the lysosomal cathepsins (B, H, L, S) and the calcium-dependent calpains. The type-1 cystatins (cystatin A, B) are intracellular proteins enriched in epithelial and hematopoietic tissues, while the type-2 cystatins (cystatin C, D, S, SA) are secreted and found in plasma, cerebrospinal fluid, saliva, and tears. Calpastatin is the sole endogenous inhibitor of calpain-1 and calpain-2 and is structurally unrelated to the cystatin superfamily. As a class, these proteins are widely studied as regulators of pericellular proteolysis, antigen presentation, and lysosomal homeostasis, and several — notably cystatin C — serve as established biomarkers in neurodegeneration and renal function research.

Triple Point Biologics has produced polyclonal antibodies against proteinases and their inhibitors since 1994, giving the catalog a depth of lot-to-lot performance data that single-lot programs cannot match. Each antibody in this collection is raised in rabbit against recombinant or synthetic peptide immunogens corresponding to defined regions of the mature protein, and epitope coordinates are documented on individual product pages. Validation data for human, mouse, and rat samples are provided where generated; cross-reactivity with additional species is noted as predicted (sequence-homology-based) or validated (empirically confirmed), never assumed. Every target in this category has a matched recombinant protein produced in the same facility, enabling direct use as a recombinant protein positive control on the same blot or tissue section — a straightforward approach to distinguishing true signal from background. See our quality and validation standards for lot-release criteria and representative validation images.

These antibodies are routinely used in matched-pair experiments pairing inhibitor detection with cathepsin activity readouts — a workflow outlined in our protease activity assays guide. Cystatin C antibodies are used in CSF and plasma studies of neurodegeneration, while cystatin A is a common marker in stratified squamous epithelium and barrier function research. Calpastatin antibodies find application in muscle biology and calpain-dependent signaling studies. For experimental designs that require inhibitor titration or dose-response controls, matched recombinant cystatins and calpastatin are available through the recombinant proteins catalog and are discussed further in our guide to recombinant protein positive controls. Researchers screening compound libraries against cysteine protease activity may find the antibody panel useful for endpoint validation alongside the protocols described in our protease inhibitor screening guide.