Perforin-1 Perforin (PRF), encoded by the PRF1 gene, is a pore-forming toxic protein housed in the secretory granules of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. Together, these cells are known as cytotoxic lymphocytes (CLs). [5]
Perforin was initially discovered in 1983 and subsequently cloned from an expression library in 1988 using anti-complement C9 antibody cross-reactivity. A sequence comparison showed a notable resemblance between the two proteins in a specific central region, termed the 'membrane attack complex/perforin' (MACPF) domain. [6]
Purifying perforin is challenging due to its tendency to lose activity and stability in solution, and only recently has a recombinant form been successfully produced. [7]
Perforin is a pore forming cytolytic protein found in the granules of cytotoxic T lymphocytes (CTLs) and natural killer cells (NK cells). Upon degranulation, perforin molecules translocate to the target cell with the help of calreticulin, which works as a chaperone protein to prevent perforin from degrading. Perforin then binds to the target cell's plasma membrane via membrane phospholipids while phosphatidylcholine binds calcium ions to increase perforin's affinity to the membrane. [8] Perforin oligomerises in a Ca2+ dependent manner to form pores on the target cell. The pore formed allows for the passive diffusion of a family of pro-apoptotic proteases, known as the granzymes, into the target cell. [9] The lytic membrane-inserting part of perforin is the MACPF domain. [10] This region shares homology with cholesterol-dependent cytolysins from Gram-positive bacteria. [11]
The initial concept of a plasma membrane pore model was challenged when research revealed that granzyme B could undergo endocytosis independently of perforin. Moreover, experiments demonstrated that apoptosis could be induced by adding perforin to washed cells that had already endocytosed granzyme B, even in the absence of perforin during the endocytosis process. In light of these findings, Froelich and colleagues suggested that perforin's action might not occur at the plasma membrane as previously thought, but rather at the endosomal membrane. [12] They proposed that perforin likely facilitates the release of granzymes from endosomes by forming pores in the endosomal membrane. [7]
Perforin has structural and functional similarities to complement component 9 (C9). Like C9, this protein creates transmembrane tubules and is capable of lysing non-specifically a variety of target cells. This protein is one of the main cytolytic proteins of cytolytic granules, and it is known to be a key effector molecule for T-cell- and natural killer-cell-mediated cytolysis. [13] Perforin is thought to act by creating holes in the plasma membrane which triggers an influx of calcium and initiates membrane repair mechanisms. These repair mechanisms bring perforin and granzymes into early endosomes. [14]
Around the turn of the 21st century, it was recognized that a total loss of perforin activity leads to a severe, fatal autosomal recessive immunoregulatory disorder in infants, known as familial hemophagocytic lymphohistiocytosis (FHL), typically appearing before 12 months of age. This condition can only be treated effectively with a bone marrow transplant from a non-related donor. [5]
The pathogenesis involves a sequence of downstream events resulting from the inability of NK cells and CTLs to present functional perforin, thereby failing to kill target cells. Infants affected by this condition typically show symptoms of "classic" familial hemophagocytic lymphohistiocytosis (FHL) and meet most or all of the criteria outlined in HLH-2004. Diagnosis is confirmed by reduced NK cell cytotoxicity, as healthy NK cells normally exhibit constitutive, pathogen-independent cytotoxicity, and by identifying mutations in genes such as PRF1, UNC13D, STX11, and STXBP2. [5]
Sub-acute perforinopathies encompass a diverse array of symptoms, all stemming from a partial ("sub-total") reduction in cytotoxic lymphocyte (CL) activity due to bi-allelic mutations in one of the four previously mentioned genes. In contrast to the acute form, diagnosing sub-acute perforinopathies can be challenging due to their typically milder and more sporadic clinical manifestations, an intermittent disease course, variability in onset age, and their frequent positive response to non-specific immune-suppressive or immune-ablative treatments. [5]
Chronic perforinopathies are regarded as a range of immune-related conditions resulting from monoallelic mutations in genes linked to familial hemophagocytic lymphohistiocytosis (FHL). These conditions typically manifest differently from classic FHL and may include conditions like blood cancers and macrophage activation syndrome, particularly in patients with juvenile rheumatoid arthritis. Onset of symptoms usually occurs after the age of 5. Moreover, some research suggests a correlation between variations in the PRF1 gene and the outcome of allogeneic bone marrow transplantation. However, these associations remain controversial, with studies disproving the connection outweighing those supporting it. [5]
Perforin has been shown to interact with calreticulin. [15]
A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens (such as viruses or bacteria), or cells that are damaged in other ways.
Granzymes are serine proteases released by cytoplasmic granules within cytotoxic T cells and natural killer (NK) cells. They induce programmed cell death (apoptosis) in the target cell, thus eliminating cells that have become cancerous or are infected with viruses or bacteria. Granzymes also kill bacteria and inhibit viral replication. In NK cells and T cells, granzymes are packaged in cytotoxic granules along with perforin. Granzymes can also be detected in the rough endoplasmic reticulum, golgi complex, and the trans-golgi reticulum. The contents of the cytotoxic granules function to permit entry of the granzymes into the target cell cytosol. The granules are released into an immune synapse formed with a target cell, where perforin mediates the delivery of the granzymes into endosomes in the target cell, and finally into the target cell cytosol. Granzymes are part of the serine esterase family. They are closely related to other immune serine proteases expressed by innate immune cells, such as neutrophil elastase and cathepsin G.
The membrane attack complex (MAC) or terminal complement complex (TCC) is a complex of proteins typically formed on the surface of pathogen cell membranes as a result of the activation of the host's complement system, and as such is an effector of the immune system. Antibody-mediated complement activation leads to MAC deposition on the surface of infected cells. Assembly of the MAC leads to pores that disrupt the cell membrane of target cells, leading to cell lysis and death.
Granzyme B (GrB) is one of the serine protease granzymes most commonly found in the granules of natural killer cells and cytotoxic T cells. It is secreted by these cells along with the pore forming protein perforin to mediate apoptosis in target cells.
Antibody-dependent cellular cytotoxicity (ADCC), also referred to as antibody-dependent cell-mediated cytotoxicity, is a mechanism of cell-mediated immune defense whereby an effector cell of the immune system kills a target cell, whose membrane-surface antigens have been bound by specific antibodies. It is one of the mechanisms through which antibodies, as part of the humoral immune response, can act to limit and contain infection.
Granzyme A is a tryptase and is one of the five granzymes encoded in the human genome. In humans, GzmA is encoded by the GZMA gene in proximity to the GZMK gene on chromosome 5. This enzyme is present in cytotoxic T lymphocyte (CTL) granules.
In immunology, an immunological synapse is the interface between an antigen-presenting cell or target cell and a lymphocyte such as a T cell, B cell, or natural killer cell. The interface was originally named after the neuronal synapse, with which it shares the main structural pattern. An immunological synapse consists of molecules involved in T cell activation, which compose typical patterns—activation clusters. Immunological synapses are the subject of much ongoing research.
In hematology, hemophagocytic lymphohistiocytosis (HLH), also known as haemophagocytic lymphohistiocytosis, and hemophagocytic or haemophagocytic syndrome, is an uncommon hematologic disorder seen more often in children than in adults. It is a life-threatening disease of severe hyperinflammation caused by uncontrolled proliferation of benign lymphocytes and macrophages that secrete high amounts of inflammatory cytokines. It is classified as one of the cytokine storm syndromes. There are inherited and non-inherited (acquired) causes of HLH.
Degranulation is a cellular process that releases antimicrobial, cytotoxic, or other molecules from secretory vesicles called granules found inside some cells. It is used by several different cells involved in the immune system, including granulocytes. It is also used by certain lymphocytes such as natural killer (NK) cells and cytotoxic T cells, whose main purpose is to destroy invading microorganisms.
Syntaxin 11, also known as STX11, is a human gene that is a member of the t-SNARE family.
Protein unc-13 homolog D, also known as munc13-4, is a protein that in humans is encoded by the UNC13D gene.
The Membrane Attack Complex/Perforin (MACPF) superfamily, sometimes referred to as the MACPF/CDC superfamily, is named after a domain that is common to the membrane attack complex (MAC) proteins of the complement system and perforin (PF). Members of this protein family are pore-forming toxins (PFTs). In eukaryotes, MACPF proteins play a role in immunity and development.
Granzyme B is a serine protease that in humans is encoded by the GZMB gene. Granzyme B is expressed by cytotoxic T lymphocytes (CTL) and natural killer (NK) cells.
Serglycin, also known as hematopoietic proteoglycan core protein or secretory granule proteoglycan core protein, is a protein that in humans is encoded by the SRGN gene. It is primarily expressed in hematopoietic cells and endothelial cells, and is the only known intracellular proteoglycan.
Granulysin (GNLY) is a protein expressed in most mammals which functions as an antimicrobial peptide released by killer lymphocytes in cytotoxic granules. It is a pore-forming peptide, as it can puncture a microbial cell wall, allowing for other death-inducing enzymes to enter the microbe and cause microptosis. GNLY is inhibited by cholesterol, and is most effective in helping to kill cholesterol-deficient microbes.
Granzyme H is a protein that in humans is encoded by the GZMH gene.
Granzyme K (GrK) is a protein that is encoded by the GZMK gene on chromosome 5 in humans. Granzymes are a family of serine proteases which have various intracellular and extracellular roles. GrK is found in granules of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), and is traditionally described as being cytotoxic towards targeted foreign, infected, or cancerous cells. NK cells and CTLs can induce apoptosis through the granule secretory pathway, which involves the secretion of granzymes along with perforin at immunological synapses.
Granzyme M is a protein that in humans is encoded by the GZMM gene.
Extranodal NK/T-cell lymphoma, nasal type (ENKTCL-NT) is a rare type of lymphoma that commonly involves midline areas of the nasal cavity, oral cavity, and/or pharynx At these sites, the disease often takes the form of massive, necrotic, and extremely disfiguring lesions. However, ENKTCL-NT can also involve the eye, larynx, lung, gastrointestinal tract, skin, and various other tissues. ENKTCL-NT mainly affects adults; it is relatively common in Asia and to lesser extents Mexico, Central America, and South America but is rare in Europe and North America. In Korea, ENKTCL-NT often involves the skin and is reported to be the most common form of cutaneous lymphoma after mycosis fungoides.
Jürg Tschopp was a Swiss biochemist, known for his research on apoptosis and the immunology of inflammation. His greatest achievement was perhaps his team's discovery and scientific description of the inflammasome.
Perforin-1 at NLM Genetics Home Reference
