Which Is a Naturally Produced Antiviral Protein in Humans?

The human body produces naturally occurring antiviral proteins called interferons. These are signaling proteins that function as a part of the innate immune system, representing a primary defense mechanism against viral infections. Discovered in 1957, interferons were named for their capacity to “interfere” with a virus’s ability to replicate within host cells. When a cell detects a viral invader, it releases interferons, which then alert neighboring cells to prepare for a potential threat.

The Primary Role of Interferons

The principal function of interferons is not to attack viruses directly but to act as an early warning system, signaling the presence of a viral threat. An infected cell releases interferons, which travel to nearby, uninfected cells and bind to specific receptors on their surfaces. This binding event initiates a protective response in the recipient cell.

This signal prompts the receiving cells to enter an “antiviral state,” where they produce proteins to combat a potential infection. One of these is protein kinase R (PKR), an enzyme that, when activated by viral components, shuts down protein synthesis within the cell. Halting the production of all proteins prevents the virus from creating the new proteins it needs to replicate.

Another induced enzyme, 2’5′-oligoadenylate synthetase, produces molecules that activate an RNase, which degrades viral RNA. Beyond preparing cells for defense, interferons also recruit other elements of the immune system. They activate immune cells like Natural Killer (NK) cells and macrophages to identify and eliminate infected cells.

How Virus Detection Triggers an Interferon Response

Most cells in the human body are equipped with specialized sensors called Pattern Recognition Receptors (PRRs). These receptors are designed to recognize molecules that are characteristic of pathogens but are not found in human cells. These pathogen-associated molecular patterns (PAMPs) include foreign genetic material like double-stranded RNA (dsRNA), which is common during the replication of many viruses.

When a PRR detects a viral PAMP, it sets off a rapid signaling cascade inside the cell. This chain of molecular events acts like a relay, carrying the message from the receptor to the cell’s nucleus. Once the signal reaches the nucleus, it activates specific genes responsible for producing interferons. The cell then begins to transcribe these genes into messenger RNA (mRNA), which is subsequently translated into interferon proteins that are then secreted from the cell.

Classifying the Types of Interferons

Interferons are a family of related proteins categorized into three main types based on the receptors they use to signal. This classification helps differentiate their specific roles and the cells that produce them, as each type contributes to the immune response in a distinct manner.

The first category, Type I interferons, includes interferon-alpha (IFN-α) and interferon-beta (IFN-β). These are considered the primary antiviral interferons and can be produced by nearly all cell types in response to a viral infection. IFN-alpha is primarily produced by leukocytes, while IFN-beta is produced in large quantities by cells called fibroblasts. Both bind to the same receptor complex, known as the IFN-α/β receptor (IFNAR), to induce the antiviral state in target cells.

Type II interferon consists of a single protein, interferon-gamma (IFN-γ). Unlike Type I interferons, IFN-γ is produced by specific immune cells, such as T-cells and NK cells, rather than by most body cells. Its primary role is less about immediate antiviral defense and more about modulating the long-term, adaptive immune response. It is an activator of macrophages and influences the activity of other immune cells.

The third group is Type III interferons, which includes interferon-lambda (IFN-λ). These interferons are specialized, primarily targeting epithelial cells, which are the cells that line the body’s surfaces, including the respiratory and gastrointestinal tracts. By focusing their action on these barrier tissues, Type III interferons establish a localized defense at common points of viral entry.

The Use of Interferons as Medical Treatment

The antiviral and immunomodulatory properties of interferons have led to their development as therapeutic agents. Scientists can produce synthetic versions of these proteins, known as recombinant interferons, for medical use.

Recombinant interferon-alpha has been a longstanding treatment for chronic viral infections, most notably Hepatitis B and Hepatitis C. Interferon-beta is a common therapy for multiple sclerosis, an autoimmune disease, where it helps to reduce the frequency and severity of relapses.

Interferon therapy is also used in oncology to treat certain types of cancer, such as melanoma, Kaposi’s sarcoma, and some leukemias. The treatment can have direct anti-tumor effects and can also stimulate the immune system to attack cancer cells. A common issue with interferon therapy is that it can cause significant side effects, including fever, muscle pain, and fatigue. These flu-like symptoms occur because the treatment activates a system-wide immune response, much like the body would during a natural infection.