Interleukin

Interleukins (IL) are a type of cytokine first thought to be expressed by leukocytes alone but have later been found to be produced by many other body cells. They play essential roles in the activation and differentiation of immune cells, as well as proliferation, maturation, migration, and adhesion. They also have pro-inflammatory and anti-inflammatory properties. The primary function of interleukins is, therefore, to modulate growth, differentiation, and activation during inflammatory and immune responses. Interleukins consist of a large group of proteins that can elicit many reactions in cells and tissues by binding to high-affinity receptors in cell surfaces. They have both paracrine and autocrine function. Interleukins are also used in animal studies to investigate aspect related to clinical medicine.

General Properties of Cytokines/Interleukins

1. Cytokines are proteins made in response to pathogens and other antigens that regulate and mediate inflammatory and immune responses.

2. Interleukin production is a self-limited process. The messenger RNA encoding most interleukins is unstable and causes a transient synthesis. These molecules are rapidly secreted once synthesized.

3. Cellular responses to interleukins include up- and down-regulatory mechanisms with the induction and participation of genes that encode inhibitors of the cytokine receptors.

4. Interleukins have redundant functions. For instance, IL-4, IL-5, and IL-13 are B-cell growth factors and stimulate B-cell differentiation.

5. Cytokines stimulate switching of antibody isotypes in B cells, differentiation of helper T cells into Th-1 and Th-2 subsets, and activation of microbicidal mechanisms in phagocytes.

6. Interleukins often influence other interleukin synthesis and actions. For instance, IL-1 promotes lymphocyte activation that leads to the release of IL-2.

7. Cellular responses to cytokines are stimulated and regulated by external signals or high-affinity receptors. For example, stimulation of B-cells by pathogens leads to increased expression of cytokine receptors.

8. Most cytokines act either on the same cell that secretes the cytokine, for instance, IL-2 produced by T cells operates on the same T cells that made it or on a nearby cell. Besides, cytokines may enter the circulation and act far from the site of production, for example, IL-1 is an endogenous pyrogen that works on the central nervous system (CNS) and causes fever.

9. Small quantities of a cytokine are needed to occupy receptors and elicit biologic effects.