Interleukin-5 (IL-5) is a protein produced by the immune system. As a cytokine, it acts as a signaling molecule, transmitting information between cells. IL-5 guides immune cells and orchestrates specific immune responses, helping the body respond to challenges.
Understanding Interleukin-5
IL-5 belongs to the Type 2 cytokine family. It is primarily produced by immune cells, including T-helper 2 (Th2) cells and mast cells. Eosinophils can also produce IL-5 upon activation. The gene for IL-5 is located on chromosome 5 in humans.
IL-5 exerts its effects by binding to specific receptors on target cells. Its most characterized effects are on eosinophils, regulating their accumulation, maturation, and survival in tissues. It also influences B cells, supporting their growth and increasing immunoglobulin secretion, particularly IgA, important for mucosal immunity.
Key Functions in Immunity
IL-5 plays a role in the biology of eosinophils, promoting their growth, maturation, survival, and activation. It acts as a factor for eosinophil differentiation and proliferation. This cytokine mobilizes eosinophils from the bone marrow, facilitating their recruitment to various tissues. IL-5 also prolongs eosinophil survival at sites of immune activity.
IL-5 also contributes to B-cell differentiation and the production of antibodies. It stimulates B-cell growth and enhances the secretion of immunoglobulins, particularly IgA. This function is especially relevant in mucosal immunity, where IgA antibodies play a protective role against pathogens at surfaces like those in the respiratory and digestive tracts. These functions are important for the body’s normal immune responses, particularly in defense against parasitic infections.
Role in Disease
Dysregulation or overexpression of Interleukin-5 can contribute to various disease states, particularly those characterized by elevated eosinophil levels, a condition known as eosinophilia. When IL-5 levels are persistently high, it can lead to an excessive accumulation and activation of eosinophils in tissues. This overactivity contributes to inflammatory processes and tissue damage in susceptible individuals.
A primary focus for IL-5’s involvement in disease is severe eosinophilic asthma. In this condition, IL-5 drives the inflammation and can contribute to airway remodeling, leading to reduced lung function and severe symptoms. High levels of IL-5 are correlated with increased numbers of circulating eosinophils and those found in airway tissues. IL-5 is also implicated in other eosinophil-driven diseases, such as hypereosinophilic syndromes (HES), a group of rare disorders marked by persistently high eosinophil counts that can affect multiple organs.
Therapeutic Approaches
Understanding the role of IL-5 in disease has led to the development of targeted therapies. These treatments aim to reduce the effects of IL-5, thereby mitigating eosinophil-driven inflammation. Monoclonal antibodies specifically designed to inhibit IL-5 have been developed.
Mepolizumab and reslizumab are examples of anti-IL-5 monoclonal antibodies that bind directly to IL-5, preventing it from interacting with its receptor on eosinophils. Another approach involves antibodies that target the IL-5 receptor itself, such as benralizumab. This type of therapy blocks the receptor, preventing IL-5 from binding and activating eosinophils. These therapies work by reducing eosinophil levels in the blood and tissues, which can alleviate symptoms and improve outcomes in conditions like severe eosinophilic asthma.