Interleukin Family: Roles and Functions

Posted on Feb 24, 2025 in Biology

  • IL-1: Produced by macrophages and epithelial cells, IL-1 induces the acute phase response. It activates T cells and macrophages, contributing to immune response development. IL-1 works alongside TNF in innate immunity and inflammation.
  • IL-2: Produced by Th1 cells, IL-2 stimulates the growth and differentiation of T lymphocytes.
  • IL-3: Produced by Th2 lymphocytes, IL-3 stimulates stem cells from bone marrow.
  • IL-4: Involved in the proliferation of B cells, mast cells, and T lymphocytes. IL-4 plays a crucial role in allergic reactions.
  • IL-5: Produced by T lymphocytes and mast cells, IL-5 stimulates the growth and proliferation of eosinophils.
  • IL-6: Secreted by macrophages, IL-6 is involved in acute phase reactions. It also stimulates the growth and differentiation of both T and B cells.
  • IL-7: A 25,000 MW glycoprotein secreted by stromal cells of the thymus, spleen, and bone marrow. IL-7 functions as a growth factor for both T cell and B cell precursors.
  • IL-8: Produced by monocytes, macrophages, keratinocytes, fibroblasts, and endothelial cells, IL-8 attracts neutrophils and naive lymphocytes. It mobilizes, activates, and induces neutrophil degranulation. IL-8 also stimulates angiogenesis.
  • IL-9: A heavily glycosylated polypeptide with a molecular weight of 30,000-40,000. IL-9 is secreted by activated T cells stimulated by IL-2. In vitro, it promotes mast cell growth. IL-9 can co-stimulate T cells with IL-2 or IL-4 and may enhance the potential of hematopoietic progenitors.
  • IL-10 (formerly Cytokine Synthesis Inhibitory Factor): An 18,000 MW protein produced by Th2 cells, CD8 T cells, monocytes, keratinocytes, and activated B cells. IL-10 inhibits activated macrophages and dendritic cells, thus controlling innate and cellular immune responses and MHC class II molecule expression.
  • IL-12 (Cytotoxic Lymphocyte Maturation Factor or NK Cell Stimulatory Factor): Synthesized primarily by macrophages and B cells. IL-12 production by activated macrophages is suppressed by IL-4 and IL-10. It promotes the proliferation of T cells and activated NK cells, increasing the latter’s lytic activity. IL-12 is a potent inducer of IFN-gamma production by resting or activated T and NK cells. It selectively induces Th0 cell differentiation into Th1 cells but suppresses Th2-dependent functions (e.g., IL-4, IL-10, and IgE antibody production). It also induces GM-CSF production.
  • IL-13: Produced by CD4 (Th2), NK, and mast cells. IL-13 promotes IgE isotype switching in B cells, increases mucus production in epithelial cells, and enhances collagen synthesis by fibroblasts and macrophages.
  • IL-14: Mediates interactions between plasma cells and the cytoplasm.
  • IL-15: Mediates T cell (CD8+ memory) growth and NK cell proliferation.
  • IL-16: A T cell-derived cytokine that acts as a specific eosinophil chemoattractant.
  • IL-17: Produced by T lymphocytes, IL-17 increases chemokine synthesis in endothelial cells and macrophages. It induces GM-CSF and G-CSF production.
  • IL-18: Produced by NK and T cells, IL-18 induces IFN-gamma synthesis.
  • IL-23: Produced by macrophages and dendritic cells, IL-23 maintains IL-17-producing T cells.
  • IL-27: Produced by macrophages and dendritic cells, IL-27 inhibits Th1 cells and induces IFN-gamma synthesis in NK cells.