Cytokines: The 6 Mediators of Innate Immunity

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The cytokines that play a major role in the mediation of natural immunity include:

  • Tumor necrosis factor (TNF alpha),
  • Interleukin 1,
  • Interleukin 10,
  • Interleukin 12,
  • Type 1 interferon (alpha and beta), and
  • Chemokines.

Tumor Necrosis Factor Alpha

Produced by activated macrophages in response to microbes especially the lipopolysaccharide layer of the gram-negative bacteria. It is an important mediator of acute inflammation. it mediates the recruitment of neutrophil and macrophages to the sites of infection by stimulating endothelial cells to produce adhesion molecules. It also acts on the hypothalamus to produce fever and promote the production of acute-phase proteins.

Interleukin 1

This is an inflammatory cytokine that is produced by activated macrophages and its effects are similar to those of tumor necrosis factor-alpha. it also helps to activate T-Cells.

Interleukin 10

Produced by activated macrophages and T- helper 2 cells. It is predominantly an inhibitory cytokine that interferes with the production of interferon-gamma by T helper 1 cells which results in a shifted immune response to T helper 2 type response. It also inhibits other cytokine produced by the activated macrophages as well as expression of class II MHC molecules and therefore generally leads to dampening of the immune response.

Interleukin 12

Produced by activated macrophages and dendritic cells. It stimulates the production of interferon-gamma and induces the differentiation of T helper cells to become T helper 1 cells. It also enhances the cytolytic function of cytotoxic T lymphocytes and the Natural Killer cells.

Type 1 Interferons

These include interferon-alpha and beta which are produced by many cells and function to inhibit the replication of cells. They also increase the expression of MHC class I molecules on cells making them more susceptible to killing by the CD8 cells. They can activate Natural Killer cells.

Interferon-gamma

This is a type II interferon produced primarily by the T helper 1 cell, but can also be produced by the CD 8 and the Natural Killer cells. It has numerous functions in both the innate and adaptive immune systems such as:

  • The induction of class I and II MHC molecules on different cell types,
  • Activation of granulocytes and macrophages,
  • Increasing the activity of Natural Killer cells, activation of T cells, and
  • Antiviral activity.

Chemokines

These are chemotactic cytokines produced by many kinds of leukocytes and other cell types. they represent a large family of molecules that function to recruit leukocytes to the site of infection and play a role in leukocyte trafficking throughout the body.

Check out a general overview of cytokines here