Interleukin-29 (IL-29) is a

cytokine Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...

and it belongs to type III interferons group, also termed interferons λ (IFN-λ). IL-29 (alternative name IFNλ1) plays an important role in the

immune response An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellula ...

against pathogenes and especially against

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are found in almo ...

by mechanisms similar to type I interferons, but targeting primarily cells of

epithelial Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

origin and

hepatocytes A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass. These cells are involved in: * Protein synthesis * Protein storage * Transformation of carbohydrates * Synthesis of cholesterol, bile ...

. IL-29 is encoded by the ''IFNL1''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

located on

chromosome 19 Chromosome 19 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 19 spans more than 61.7 million base pairs, the building material of DNA. It is considered the most Gene density, gene-ri ...

in humans. It is a

pseudogene Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Pseudogenes can be formed from both protein-coding genes and non-coding genes. In the case of protein-coding genes, most pseudogenes arise as superfluous copies of fun ...

in mice meaning the IL-29 protein is not produced in them.

Structure

IL-29 is, with the rest of IFN-λ, structurally related to the

IL-10 family The IL-10 family is a family of interleukins. In addition to IL-10, it includes IL-19, IL-20, IL-22, IL-24 and IL-26. Some sources also include the interferons IL-28 and IL-29. The IL-10 family are helical cytokines categorized based on ...

, but its primary

amino acid sequence Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...

(and also function) is more similar to type I interferons. It binds to a

heterodimeric In biochemistry, a protein dimer is a macromolecular complex or multimer formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ...

receptor Receptor may refer to: * Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...

composed of one subunit IFNL1R specific for IFN-λ and a second subunit IL10RB shared among the IL-10 family cytokines.

Function

Effects on immune response to pathogens

IL-29 exhibits antiviral effects by inducing similar

signaling pathways Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events. Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term ...

as type I interferons. IL-29 receptor signals through JAK-STAT pathways leading to activated expression of interferon-stimulated genes and production of antiviral proteins. Further consequences of IL-29 signalization comprise the

upregulated In biochemistry, in the biological context of organisms' regulation of gene expression and production of gene products, downregulation is the process by which a cell decreases the production and quantities of its cellular components, such as RNA ...

expression of

MHC class I MHC class I molecules are one of two primary classes of major histocompatibility complex (MHC) molecules (the other being MHC class II) and are found on the cell surface of all nucleated cells in the bodies of vertebrates. They also occur on ...

molecules, or enhanced expression of the costimulatory molecules and

chemokine Chemokines (), or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In addit ...

receptors on pDC, which are the main producers of

IFN-α The type-I interferons (IFN) are cytokines which play essential roles in inflammation, immunoregulation, tumor cells recognition, and T-cell responses. In the human genome, a cluster of thirteen functional IFN genes is located at the 9p21.3 cyt ...

. IL-29 expression is dominant in virus-infected epithelial cells of the

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...

gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

and

urogenital The genitourinary system, or urogenital system, are the sex organs of the reproductive system and the organ (biology), organs of the urinary system. These are grouped together because of their proximity to each other, Development of the urinary a ...

tracts, also in other mucosal tissues and

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

. Hepatocytes infected by HCV or HBV viruses stimulate the immune response by producing IL-29 (IFN-λ in general) rather than type I interferons. It is also produced by maturing macrophages, dendritic cells or mastocytes. It plays a role in defense against

pathogens In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term ...

apart from viruses. It affects the function of both

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