Interleukin-7, or IL-7, is a protein that functions as a messenger within the immune system. As a type of protein known as a cytokine, it helps coordinate the body’s response to infection and disease. IL-7 provides instructions that regulate the development and function of various immune cells, helping to keep the immune system balanced and ready to defend the body.
Role in Immune Cell Development
Interleukin-7 has a defined function in lymphopoiesis, the generation of immune cells called lymphocytes. It is particularly influential in the development of T-cells, which mature in the thymus. Here, IL-7 acts as a growth and survival signal for immature T-cell precursors, guiding them through their early development and ensuring a sufficient number are produced.
The protein also contributes to the development of B-cells in the bone marrow, though its role in human B-cell development is less pronounced than in mice. The signals from IL-7 are delivered by stromal cells, which are connective tissue cells in the bone marrow and thymus. These stromal cells create a supportive microenvironment where developing lymphocytes receive instructions for maturation, preventing them from undergoing programmed cell death.
The interaction between IL-7 and its receptor on the surface of young immune cells triggers internal signals that promote their growth and differentiation. Without these signals, the development of lymphocyte populations would be significantly impaired, leading to a compromised immune system.
Maintenance of Immune Memory
Beyond creating new immune cells, Interleukin-7 is also involved in sustaining the pool of mature lymphocytes. This is especially true for memory T-cells, which are long-lived cells that “remember” previous infections. IL-7 helps maintain the cells responsible for this ability, allowing the immune system to respond more quickly to pathogens it has encountered before.
Memory T-cells persist in the body for years, ready to mount a rapid defense upon re-exposure to a specific pathogen. IL-7 provides constant, low-level survival signals to these cells, ensuring they remain alive and functional. This process of homeostasis keeps the number of memory T-cells stable, preserving the body’s immunological memory.
This role in maintenance is distinct from its function in development. Instead of building new cells from scratch, this function preserves the existing, experienced cells circulating in the body. By sustaining these memory T-cell populations, IL-7 ensures the immune system retains its ability to fight off pathogens it has previously defeated.
Involvement in Disease Processes
When the Interleukin-7 signaling pathway is not properly regulated, it can contribute to various diseases. In autoimmune disorders, the immune system mistakenly attacks the body’s own tissues. Excessive IL-7 signaling can promote the survival and activation of self-reactive T-cells, and elevated levels of IL-7 have been observed in conditions like multiple sclerosis and rheumatoid arthritis.
In cancer, IL-7 has a complex role. Certain cancers, particularly those involving T-cells like T-cell acute lymphoblastic leukemia (T-ALL), can become dependent on IL-7 for growth and survival. These cancer cells exploit the normal IL-7 signaling pathway to promote their own proliferation. Researchers have identified mutations in the IL-7 receptor gene in some leukemia patients, which cause the receptor to be constantly “on,” driving uncontrolled cell growth.
The same signals that support the development of healthy T-cells can be hijacked by malignant cells or contribute to harmful autoimmune responses. Understanding how IL-7 contributes to these disease processes has opened new avenues for therapeutic interventions aimed at blocking its effects.
Therapeutic Potential and Applications
Scientists are exploring Interleukin-7 as a therapeutic agent to enhance immune function. One area of research is cancer immunotherapy, which aims to boost the body’s immune system to fight tumors. Administering IL-7 can increase the number and effectiveness of T-cells and is being tested in combination with treatments like CAR T-cell therapy to improve their efficacy.
Another application is in immune reconstitution for patients with weakened immune systems. Individuals who have undergone chemotherapy or a bone marrow transplant often have low T-cell counts, leaving them vulnerable to infections. Clinical trials show that IL-7 can help restore these T-cell populations more quickly. A similar approach is being investigated for individuals with HIV.
There is also interest in using IL-7 as a vaccine adjuvant, a substance added to a vaccine to improve the resulting immune response. By promoting the proliferation and survival of T-cells that respond to vaccine antigens, IL-7 could help generate a stronger and more durable immune memory.