What Are the Roles and Functions of Interleukins?

Interleukins are a large family of cytokines—small, soluble signaling proteins—that play pivotal roles in regulating immune responses, inflammation, hematopoiesis, and tissue repair. First identified in the 1970s during studies of lymphocyte communication, interleukins are primarily secreted by leukocytes—including T cells, B cells, macrophages, and dendritic cells—but are also produced by endothelial cells, fibroblasts, and epithelial cells under inflammatory or stress conditions.

Over 40 distinct interleukins have been characterized to date (designated IL-1 through IL-40 and beyond), each with unique receptor complexes and downstream signaling pathways—most commonly involving JAK-STAT, NF-κB, or MAPK cascades. Their biological effects are highly context-dependent: some promote inflammation (e.g., IL-1β, IL-6, IL-12, IL-17, IL-23), while others suppress immune activation and maintain tolerance (e.g., IL-10, IL-35). Several interleukins drive lymphocyte differentiation—IL-2 supports regulatory T-cell expansion and effector T-cell proliferation; IL-4 induces Th2 polarization; IL-12 and IL-23 guide Th1 and Th17 development, respectively; and IL-7 is essential for lymphoid progenitor survival and naïve T-cell homeostasis.

Clinically, interleukins serve as both therapeutic targets and biologic agents. Monoclonal antibodies blocking IL-4Rα (e.g., dupilumab), IL-5 (e.g., mepolizumab, benralizumab), or IL-17A (e.g., secukinumab) are now standard-of-care for allergic asthma, eosinophilic disorders, and psoriatic disease. Conversely, recombinant IL-2 (aldesleukin) is FDA-approved for metastatic melanoma and renal cell carcinoma, leveraging its ability to expand cytotoxic T cells and natural killer cells—though its use is limited by systemic toxicity. Emerging research explores engineered interleukin variants with improved pharmacokinetics and selective receptor engagement to enhance efficacy and reduce off-target effects.

Dysregulation of interleukin signaling underpins numerous pathologies: gain-of-function mutations in IL-1 pathway genes cause autoinflammatory syndromes like CAPS (cryopyrin-associated periodic syndromes); chronically elevated IL-6 contributes to rheumatoid arthritis and cytokine release syndrome; and aberrant IL-23/Th17 axis activity drives inflammatory bowel disease and ankylosing spondylitis. Ongoing clinical trials continue to evaluate novel interleukin modulators across oncology, immunology, and neurology—highlighting their enduring centrality in modern molecular medicine.