‏cytokines ‎السايتوكينات

CYTOKINES AND ITS TYPES:

INTRODUCTION:

- The term "cytokine" is derived from a combination of two Greek words - "cyto" meaning cell and "kinos" meaning movement. 

- Cytokines are cell signalling molecules that aid cell to cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma.

- Examples of cytokines include the agents interleukin and the interferon which are involved in regulating the immune system's response to inflammation and infection.

- In addition to mediating and regulating immune responses, cytokines are also involved in the production and development of all the different types of blood cells (through a process known as haematopoiesis), angiogenesis as well as tumorigenesis among a few other important functions.

TYPES OF CYTOKINES:

1. Interferons

2. Chemokines

3. Interleukins (many interleukins are considered to be lymphokines)

4. TNF (tumor necrosis factor)

1. INTERFERONS:

- Interferon is a family consisting of widely expressed signaling proteins. Like the other cytokines, interferons are also released by cells of the host's immune system in response to such invading organisms as bacteria and viruses.

- They are also released to respond to tumorous cells in some organisms. Currently, three types of interferons have been identified. These include Type I IFNs, Type II IFN, and Type III IFNs. 

2. INTERLUKINS:

- Produced by such leukocytes as lymphocytes and monocytes (and a number of other cells in the body e.g. ) interleukins are glycoproteins involved in the activation and differentiation of immune cells. In addition, they also play an important role in the proliferation, migration, maturation, pro and anti-inflammatory activities, as well as adhesion of these cells. 

- Together with interleukin receptors, interleukins belong to a superfamily (IL superfamily) that is made up of proteins. While it's easy to generalize the functions of these cytokines, this is largely dependent on the type of interleukins. Currently, over 43 members of this superfamily have been identified (IL-1 to IL-43).

- Like some of the other cytokines, interleukins are made up of proteins. Typically, this is in response to invading pathogens/antigens. While high volumes may be produced depending on the type of interleukins and the invading organism, a small quantity of the molecule is required to activate biological effects.

- Some of the other properties of interleukins include:

- Synthesis is a self-limited process

- Stimulate up-regulatory and down-regulatory mechanisms

- Have redundant functions in the body - Given interleukins can cause different effects on various types of cells

- Can influence the synthesis and functioning of other interleukins

3. CHEMOKINES:

- Chemokines are a type of protein cytokine that play an important role in chemotaxis. As such, there may be signals that guide certain immune cells to the affected site.

- Currently, about 50 chemokines have been identified. They are divided into four families based on the location of N-terminal cysteine residues in their three-dimensional structure.

4. TUMORS NECROSIS FECTOR:

- Tumor Necrosis Factor (TNF) consists of a group of proteins involved in a number of physiological and pathological processes. Currently, about 40 members of the superfamily (TNF) have been identified with TNF-α and TNF-β being the most notable examples.

Some of the other members of TNF include:

- CD40 ligand

- OX40 ligand

- FAS ligand

- GITR ligand

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