What is apoptosis?

Cell apoptosis, also known as programmed cell death, is a highly regulated process that not only allows for proper growth and development by ridding the organism of unneeded cells and tissues, but also minimizes threats to the organism by destroying surplus cells of the immune system and virus-infected or DNA-damaged cells [1].

Programmed cell death is morphologically and biochemically distinct from cell death by injury (necrosis). Unlike necrotic cells, apoptotic cells exhibit compaction of the nuclear chromatin, shrinkage of the cytoplasm, and production of membrane-bound apoptotic bodies, as well as DNA fragmentation and cleavage or degradation of several cellular proteins (Figure 1). Biochemically, apoptosis is distinguished by fragmentation of the genome and cleavage or degradation of several cellular proteins. Incorrectly regulated apoptosis is implicated in a number of disease states, including cancer, stroke, Alzheimer’s disease, and several autoimmune diseases.

Apoptosis can be induced through three different pathways: 1) targeting mitochondria functionality (mitochondrial, cellular or apoptosis intrinsic pathway), 2) direct transduction of the signal via adaptor proteins (death-receptor or apoptosis extrinsic pathway) and 3) the perforin/granzyme pathway [2-3].

Illustration of the differences in cellular processes of a cell undergoing apoptosis vs necrosis

Figure 1. Comparison of apoptosis and necrosis.

Identifying cells that are going through apoptosis can be challenging because many of the assays used as indicators are detecting structural and functional changes that occur in other processes as well. Additionally, no single parameter fully defines programmed cell death in all systems and the appearance of these changes can vary with apoptotic pathway or cell types. Therefore, it is often advantageous to use several different assays to detect cell apoptosis.

Interested in the non-apoptotic form of cell death? Learn more about Ferroptosis Research Solutions.

Apoptosis assays for cell structure, function, and physiology

3D image of mitochondria

Mitochondria function and membrane potential assays

A distinctive feature of apoptosis is the disruption of active mitochondria, which includes changes in the membrane potential and alterations to the oxidation–reduction potential of the mitochondria.

bivariant plot of live, dead, necrotic cells

Caspase enzyme activity assays

The activation of caspase enzymes occurs very early in the apoptotic process. These enzymes have been identified as crucial mediators of the complex biochemical events associated with apoptosis.

fluorescent image of cell

DNA fragmentation and morphological assays

The characteristic breakdown of the nucleus during apoptosis includes collapse and fragmentation of the DNA, degradation of the nuclear envelope and nuclear blebbing, resulting in the formation of micronuclei.

schematic of annexin binding to the plasma membrane

Plasma membrane integrity and asymmetry assays

Changes in the cell’s membrane include distortion of the cell membrane, changes in the lipid composition and membrane integrity, and translocation of the phospholipid phosphatidylserine.

Additional reagents to monitor apoptotic cell physiology


Changes in the cell cytosol also occur during apoptosis, with variations in cellular ion concentration, pH, and level of reactive oxygen species (ROS).

cells stained with orange cytoplasm, green mitochondria, blue nuclei

Classic products for cell viability and autophagy can also be used to help characterize and identify cells undergoing apoptosis.

Tools for analyzing apoptosis pathways

Apoptosis is a highly regulated process and involves a significant number of signaling pathways. Thermo Fisher Scientific offers a wide range of primary antibodies, ELISA kits, multiplexed immunoassays, peptides and recombinant proteins as well as genomic assays targeted to specific proteins. Below is just an example of the types of assays we have available for some key apoptosis proteins.

Table 2. Example of products for key apoptosis pathway proteins.

ProteinFull namePrimary antibodiesELISA KitsProteins/peptidesTaqMan® assays
AIFApoptosis inducing factorAIF antibodies AIF proteins/peptidesAIF TaqMan® Assays
AIF-1/IBA1Allograft inflammatory factor 1AIF-1/IBA1 antibodies  AIF-1/IBA1 TaqMan® Assays
Apaf-1Apoptotic protease activating factorApaf-1 antibodies  Apaf-1 TaqMan® Assays
Bcl Protein Family
(Bcl-2, Bcl-10, Bcl-x, Bcl-xL, Bcl-xS, BCL-w)
B-cell lymphoma proteinBcl Protein Family antibodiesBcl Protein Family ELISAsBcl Protein Family proteins/peptidesBcl Protein Family TaqMan® Assays
t-BID/BID-p15Truncated BH3-interacting domain death agonist;  BH3-interacting domain death agonist p15t-BID/BID-p15 antibodiesBID ELISAs t-BID/BID-p15 TaqMan® Assays
BIM/BCL2L11Bcl-2-like protein 11BIM antibodies BIM proteinsBIM TaqMan® Assays
BADBcl2-associated agonist of cell deathBAD antibodies  BAD TaqMan® Assays
BAKBcl-2 homologous antagonist/killerBAK antibodies  BAK TaqMan® Assays
BNIP3BCL2/adenovirus E1B 19 kDa protein-interacting protein 3BNIP3 antibodies  BNIP3 TaqMan® Assays
Caspase-3Cysteinyl aspartic acid-protease-3Caspase-3 antibodiesCaspase-3 ELISAsCaspase-3 proteins/peptidesCaspase-3 TaqMan® Assays
Caspase-7Cysteinyl aspartic acid-protease-7Caspase-7 antibodiesCaspase-7 ELISAsCaspase-7 proteins/peptidesCaspase-7 TaqMan® Assays
Caspase-9Cysteinyl aspartic acid-protease-9Caspase-9 antibodiesCaspase-9 ELISAsCaspase-9 proteins/peptidesCaspase-9 TaqMan® Assays
cIAP1/BIRC2Cellular inhibitor of apoptosis protein 1; Baculoviral IAP repeat-containing protein 2cIAP1/BIRC2cIAP1 ELISAs 1cIAP1 proteins/peptidescIAP1 TaqMan® Assays
cIAP2/BIRC3Cellular inhibitor of apoptosis protein 2; Baculoviral IAP repeat-containing protein 3cIAP2/BIRC3  cIAP2 TaqMan® Assays
Cytochrome c Cytochrome c antibodiesCytochrome c ELISAs Cytochrome c TaqMan® Assays
FADDFAS-associated death domain protein

FADD antibodies

  FADD TaqMan® Assays
Fas/CD95 Fas/CD95 antibodiesFas/CD95 ELISAsFas/CD95 proteins/peptidesFas/CD95 TaqMan® Assays
Fas-ligand/CD178 Fas-ligand/CD178 antibodiesFas-ligand/CD178 ELISAs Fas-ligand/CD178 TaqMan® Assays
MCL-1Myeloid cell leukemia-1

MCL-1 antibodies

MCL-1 ELISAsMCL-1 proteins/peptidesMCL-1 TaqMan® Assays
Smac/DIABLOSecond mitochondrial activator of caspases/directSmac/DIABLO antibodiesSmac/DIABLO ELISAsSmac/DIABLO proteins/peptidesSmac/DIABLO TaqMan® Assays

Learn more about the Cellular Apoptosis Pathway, Apoptosis Death Receptor Pathway and the CTL-Mediated Apoptosis Pathway

Related apoptosis assays and reagents

For Research Use Only. Not for use in diagnostic procedures.