Interleukins are small proteins that form a communication network within the body’s immune system. They act as messengers, allowing immune cells to “talk” to one another and coordinate responses against invaders like bacteria, viruses, and abnormal cells. Their precise signaling helps the immune system identify and eliminate threats while maintaining bodily balance.
What Are Interleukins?
Interleukins are a type of cytokine, which are signaling proteins produced by various cells, primarily those of the immune system. They are small proteins or glycoproteins. While their name “interleukin” reflects an early belief that they only facilitated communication between leukocytes (white blood cells), it is now known that many non-immune cells also produce or respond to them.
Their production is regulated in response to stimuli like infection or tissue damage. The diverse range of interleukins allows for specific signals to be transmitted throughout the body.
How Interleukins Communicate
Interleukins transmit signals by binding to specific receptor proteins on the surface of target cells. This interaction is often compared to a “lock and key” mechanism, where each interleukin fits precisely into its corresponding receptor. Once bound, it triggers biochemical reactions inside the target cell, leading to a specific change in the cell’s behavior or function.
Different interleukins bind to different receptors. A single cell type may have many kinds of receptors, allowing it to respond to multiple interleukin signals. The outcome can vary widely, from stimulating a cell to divide, to altering its gene expression, or even instructing it to undergo programmed cell death.
Diverse Functions in Immunity
Interleukins orchestrate a wide range of immune responses, with roles in both initiating and resolving immune challenges.
Driving Inflammation
Some interleukins, such as Interleukin-1 (IL-1), Interleukin-6 (IL-6), and Interleukin-8 (IL-8), drive inflammation. IL-1 and IL-6 contribute to fever and recruit immune cells to sites of infection or injury. IL-8 primarily acts as a chemoattractant, guiding neutrophils to inflammatory sites.
Cell Growth and Differentiation
Other interleukins are important for the growth and differentiation of immune cells. Interleukin-2 (IL-2) promotes the proliferation of T lymphocytes. Interleukin-4 (IL-4) guides B cells towards antibody production and influences T helper cell differentiation. Interleukin-7 (IL-7) supports the development and survival of T and B lymphocytes in the bone marrow and thymus.
Regulating Immune Responses
Certain interleukins dampen or regulate immune responses to prevent excessive inflammation or autoimmunity. Interleukin-10 (IL-10) suppresses the activity of various immune cells, helping to resolve inflammation and maintain tolerance to the body’s own tissues. Transforming Growth Factor-beta (TGF-beta), while not strictly an interleukin, often works with IL-10 to suppress immune cell activation.
Coordinating Defenses
Interleukins also coordinate defenses against infections and abnormal cells. Interleukin-12 (IL-12) helps steer the immune response against intracellular pathogens and cancer by promoting T helper 1 cells and natural killer cell activity. Interleukin-15 (IL-15) supports the survival and proliferation of natural killer cells and certain T cells, contributing to antiviral and antitumor immunity.
Interleukins and Health Conditions
Dysregulation of interleukin activity, whether too much or too little, can contribute to various health conditions.
Autoimmune Diseases
In autoimmune diseases like rheumatoid arthritis and Crohn’s disease, an imbalance of specific interleukins leads the immune system to mistakenly attack the body’s own tissues. Elevated levels of IL-6 are often seen in rheumatoid arthritis, contributing to joint inflammation and damage. IL-23 and IL-12 are implicated in inflammatory processes in Crohn’s disease and psoriasis.
Chronic Inflammatory Conditions
Chronic inflammatory conditions, such as asthma and psoriasis, are driven by persistent interleukin signaling. In asthma, IL-4, IL-5, and IL-13 promote allergic inflammation, airway hyperresponsiveness, and mucus production. Psoriasis involves an inflammatory cascade influenced by IL-17 and IL-23, which promote rapid skin cell proliferation and immune cell recruitment.
Severe Infections and Cancer
During severe infections, an excessive immune response involving interleukins can become detrimental, as seen in sepsis. A large release of pro-inflammatory interleukins like IL-1 and IL-6 can lead to widespread inflammation, organ dysfunction, and shock. In cancer, certain interleukins might promote tumor growth by fostering an inflammatory environment or suppressing anti-tumor immunity.
Interleukins in Medicine
Understanding the roles of interleukins has opened new avenues for diagnostic tools and therapeutic interventions.
Therapeutic Interventions
Biologic drugs are designed to modulate interleukin activity. For instance, anti-IL-6 receptor antibodies, such as tocilizumab, treat rheumatoid arthritis by blocking IL-6 signaling, reducing inflammation and joint damage. Drugs targeting IL-17 and IL-23 have been developed for psoriasis, dampening the inflammatory response in the skin.
Some therapies aim to mimic or enhance interleukin functions. Recombinant IL-2, for example, is used in certain cancer immunotherapies to stimulate the proliferation and activity of T cells and natural killer cells, boosting the body’s anti-tumor response.
Diagnostic Markers
Measuring interleukin levels in blood or other bodily fluids serves as diagnostic markers. Elevated levels of specific interleukins can indicate disease activity, help diagnose conditions, or monitor a patient’s response to treatment. This provides insights into inflammatory or immune processes, guiding treatment decisions.