Granzyme A vs Granzyme B — Antibody Selection Guide

Researchers often group granzyme A and granzyme B as interchangeable markers of cytotoxic lymphocyte activation, yet these proteases execute distinct biochemical pathways. While both contribute to target cell elimination, granzyme A cleaves after basic residues (Lys/Arg) and triggers pyroptosis through gasdermin-B, whereas granzyme B exhibits strict aspartate specificity and activates both caspase-dependent apoptosis and gasdermin-E-mediated pyroptosis. This functional divergence means antibody selection depends on the specific cell death pathway, substrate, or mechanistic question under investigation.

Quick Comparison Table

When to Choose Granzyme A

Granzyme A antibodies are appropriate when investigating caspase-independent cell death mechanisms in cytotoxic lymphocyte function. Because granzyme A cleaves gasdermin-B (GSDMB) at Lys-244 to release the pore-forming N-terminal domain, researchers studying pyroptosis in human tumor cells or infected cells should prioritize granzyme A detection. This pathway is particularly relevant in contexts where caspase inhibitors fail to rescue target cells from CTL-mediated killing, indicating non-apoptotic death.

Granzyme A is the dominant granzyme in certain lymphocyte subsets, including γδ T cells and a fraction of CD8+ memory T cells. In studies of chronic viral infections (HIV, HCV, CMV), elevated granzyme A without corresponding granzyme B upregulation has been documented in exhausted or dysfunctional T cell populations. Antibody staining for granzyme A can therefore distinguish functional states within cytotoxic compartments that granzyme B alone would miss.

The protease also plays non-cytotoxic roles through cleavage of extracellular matrix proteins and pro-inflammatory substrates. Granzyme A has been detected in synovial fluid of rheumatoid arthritis patients and in skin lesions of lupus erythematosus, where it contributes to tissue damage independent of classical target cell killing. Researchers modeling autoimmune pathology or transplant rejection may find granzyme A more informative than granzyme B for tracking inflammatory granzyme activity outside the immunological synapse.

Western blot analysis of granzyme A yields a band at approximately 29 kDa, and the enzyme is often processed from a slightly larger proform. In immunohistochemistry, granzyme A localizes to cytoplasmic granules in resting CTLs and NK cells, with diffuse cytoplasmic or secreted staining upon activation. Triple Point Biologics' granzyme A antibody is validated for Western blot; additional application validation in progress in human tissues.

When to Choose Granzyme B

Granzyme B antibodies are the standard choice for assessing classical CTL and NK cell cytotoxic function, particularly in studies of tumor immunology and checkpoint inhibitor therapy. Granzyme B cleaves gasdermin-E (GSDME) at Asp-270 in cells expressing this gasdermin family member, triggering pyroptosis, and simultaneously activates executioner caspases (caspase-3 and caspase-7) by direct cleavage at aspartate residues. This dual-pathway mechanism makes granzyme B the principal mediator of rapid target cell elimination in most experimental systems.

In cancer immunotherapy research, granzyme B expression and secretion serve as pharmacodynamic biomarkers of T cell activation following immune checkpoint blockade, CAR-T cell infusion, or bispecific antibody treatment. Tumor-infiltrating lymphocytes with high granzyme B content correlate with favorable prognosis in melanoma, breast, and colorectal cancers. Immunohistochemical detection of granzyme B in tumor sections enables spatial analysis of cytotoxic infiltrates relative to tumor nests, stromal boundaries, and tertiary lymphoid structures.

Granzyme B is also expressed at lower levels in regulatory T cell subsets and has been implicated in Treg-mediated suppression through direct killing of effector T cells or antigen-presenting cells. This non-conventional expression pattern is relevant in transplant tolerance, autoimmune disease, and tumor immune evasion models. Researchers investigating Treg function should confirm granzyme B positivity in CD4+CD25+FoxP3+ populations, which granzyme A typically does not mark.

On Western blot, granzyme B migrates at approximately 27 kDa. The protein is synthesized as an inactive zymogen and activated by cathepsin C-mediated cleavage of an N-terminal dipeptide. Researchers studying granule biogenesis or protease maturation can use granzyme B antibodies to distinguish proforms from mature enzyme. Triple Point Biologics' granzyme B antibody recognizes both pro- and mature forms in Western blot, immunohistochemistry, and immunofluorescence applications across human samples.

Can They Be Used Together?

Dual detection of granzyme A and granzyme B provides a more complete profile of cytotoxic lymphocyte effector differentiation and activation state. The two proteases are not always co-expressed at equivalent levels; granzyme B is typically more abundant in acutely activated CTLs and NK cells, whereas granzyme A predominates in certain memory subsets and during chronic stimulation. Simultaneous immunofluorescence staining permits single-cell resolution of granzyme expression patterns within heterogeneous lymphocyte populations infiltrating tumors or infected tissues.

Sequential Western blot analysis using both antibodies on the same lysate distinguishes the two granzymes by molecular weight (granzyme A at ~29 kDa, granzyme B at ~27 kDa), although migration differences of only 2 kDa require careful gel resolution. Stripping and reprobing membranes, or running duplicate gels, enables direct comparison of expression levels across experimental conditions such as T cell activation time courses, cytokine treatments, or patient cohorts.

In mechanistic studies of cell death pathways, paired detection clarifies which granzyme mediates killing in a given system. For example, tumor cells lacking caspase-3 and GSDME may resist granzyme B but remain susceptible to granzyme A-induced pyroptosis via gasdermin-B cleavage. Conversely, cells with low GSDMB expression depend on granzyme B for efficient lysis. Co-staining target cells for cleaved gasdermin-B (granzyme A pathway) and cleaved caspase-3 (granzyme B pathway) alongside granzyme antibodies resolves the active mechanism.

Researchers should note that both antibodies are raised in rabbit, precluding simultaneous direct immunofluorescence without additional conjugation strategies or sequential staining protocols. For flow cytometry panels requiring both targets, consider using one directly conjugated antibody and one requiring secondary detection, or employ sequential permeabilization and staining rounds.

Cross-Reactivity Considerations

Granzyme A and granzyme B share approximately 40% sequence identity and belong to the same serine protease superfamily, but their substrate-binding pockets and surface loops differ substantially due to divergent substrate specificities. Well-characterized antibodies raised against full-length or C-terminal regions of each granzyme exhibit minimal cross-reactivity, although this should be confirmed by the vendor through Western blot of recombinant proteins or knockout cell lysates.

Triple Point Biologics' granzyme A and granzyme B antibodies are raised against distinct immunogens and have been validated to recognize their respective targets without cross-reaction to the other granzyme family member. Researchers working with other granzyme family members (granzyme H, K, M) should verify specificity if these proteases are co-expressed in the experimental system, although CTLs and NK cells predominantly express granzyme A and B.

In tissues with high expression of both granzymes, such as activated NK cells or effector memory CTLs, specificity can be confirmed by parallel staining of serial sections or duplicate blots. Pre-adsorption controls using recombinant granzyme A or B protein, where available, provide additional confidence in single-target specificity. Knockout or knockdown cell lines offer the most definitive specificity control when cross-reactivity is a concern.

Triple Point Biologics Antibody Specifications

Triple Point Biologics has supplied proteinase and proteinase inhibitor antibodies to the research community since 1994. Both granzyme antibodies are rabbit polyclonal antibodies validated for Western blot; additional application validation in progress. Cross-reactivity with mouse and rat granzymes is predicted based on sequence homology but should be confirmed empirically for non-human studies.

The granzyme A antibody recognizes the 262-amino acid human granzyme A (UniProt P12544, EC 3.4.21.78) and detects a band at approximately 29 kDa by Western blot. The antibody is supplied as purified IgG and is suitable for detection of granzyme A in CTL, NK cell, and γδ T cell lysates, as well as in formalin-fixed paraffin-embedded tissue sections.

The granzyme B antibody recognizes the 247-amino acid human granzyme B (UniProt P10144, EC 3.4.21.79) and detects a band at approximately 27 kDa by Western blot. The antibody recognizes both pro- and mature forms of the enzyme and is validated for immunohistochemical detection of granzyme B-positive lymphocytes in tumor-infiltrating lymphocyte studies, transplant pathology, and autoimmune tissue sections.

Both antibodies are provided with recommended dilutions for each application and are compatible with standard protocols for Western blot (1:1000–1:2000), immunohistochemistry on paraffin sections (1:100–1:500), and immunofluorescence (1:100–1:200). Researchers are encouraged to optimize dilutions for their specific tissue or cell type.

References

1. Zhou Z, He H, Wang K, et al. Granzyme A from cytotoxic lymphocytes cleaves GSDMB to trigger pyroptosis in target cells. Science. 2020;368(6494):eaaz7548.
2. Zhang Z, Zhang Y, Xia S, et al. Gasdermin E suppresses tumour growth by activating anti-tumour immunity. Nature. 2020;579(7799):415-420.
3. Chowdhury D, Lieberman J. Death by a thousand cuts: granzyme pathways of programmed cell death. Annu Rev Immunol. 2008;26:389-420.
4. Trapani JA, Smyth MJ. Functional significance of the perforin/granzyme cell death pathway. Nat Rev Immunol. 2002;2(10):735-747.