Interleukin-16

Interleukins (from Latin/Greek inter = between; leukos = white; kinein = to move) are a group of endogenous, short-chain regulatory proteins (cytokines) of the immune system (IL1-IL38). Interleukins are mediators for induction, course and control of T-cell-mediated cytotoxic immune reactions as well as B-cell activation (antibody production). They are mainly formed and secreted by stimulated leukocytes, monocytes and macrophages. So far, about 38 different interleukins have been clearly identified. Each cytokine of the interleukin group is nomenclatically assigned a number for its classification (IL-1 to IL-38).

Interleukin-16 is a pleiotropic, growth-promoting cytokine that is primarily produced by T-cells that express the CD8 antigen. The cytokine acts as a chemoattractant, modulator of T cell activation, and inhibitor of HIV replication. The coding interleukin-16 gene is located on chromosome 15.

The release of interleukin-16 is stimulated by histamine. The cytokine is formed and secreted by mast cells, eosinophilic granulocytes, CD4+T cells and macrophages.

The cytokine does not resemble any other member of a known cytokine family. Originally, Interleukin-16 was named "Lymphocyte chemoattractant factor (LCF)" after its skin ppt function.

Interleukin-16 is primarily formed as an 80 kDa precursor peptide (Pro-IL-16). This precursor peptide is cleaved by a proteolytic enzyme (caspase-3) into a 14 kDa monomer, which then aggregates to form the actual biologically active homotetramer. Interleukin-16 binds via CD4 (which thus also performs the function of a cytokine receptor).

Dormant CD4+ cells then resume their division activity and enter the G1 phase of the cell cycle. At the same time, it promotes the expression of the interleukin-2 receptor on T lymphocytes. As a result of this receptor expression, T cells proliferate after exposure to interleukin-2 and -16. Via T cell activation, interleukin-16 binds to monocytes, eosinophilic granulocytes and dendritic cells. Cells lacking CD4 cannot react to interleukin-16.

Increases in interleukin-16 levels are observed in a number of aetiologically different diseases. Their significance remains to be seen.

IL-16 is elevated in both acute and chronic atopic eczema and can serve as a marker for disease activity.

Furthermore, increases in interleukin levels are found in ovarian cancer, obesity and multiple sclerosis.

Polymorphisms of the interleukin-16 gene lead to an increased risk of developing a glioma (genotype: rs11556218 T/G). Furthermore, polymorphisms of the gene have been detected in contact sensitizations.

Interleukin-16 plays an additive role in blocking the replication of the HIV virus in CD4+ lymphocytes. Its role in Crohn's disease, multiple sclerosis, and autoimmune thyroiditis still needs to be explained.

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