Cytokines play a major role in the stimulation of the hematopoiesis of immune cells. They mainly act upon immature cells by increasing their maturation and  proliferation. Another important activity of cytokines is the chemotaxis of leucocytes to affected areas. This is one of the defense mechanisms of both innate and adaptive immunity. Both reactions are mediated by different cytokines, which are mainly produced by the immune cells. Some of them are produced by other types of cells however.  

Cytokines  that produce hematopoiesis stimulation.

The other functional group of cytokines is known as hematopoiesis-stimulating cytokines. Due to the large cell cost involved in the immune response, a system that allows the recovery of the cell numbers is necessary in order to be prepared against following infections. Those cytokines with this activity have their effect mainly upon immature cells, favoring their maturation and proliferation. Many  cytokines can have this role, although the most important are:  

Main cytokines that stimulate hematopoiesis. 

Most  of them present a monomeric structure, with monomers of 19-26 Kd, with the exception of M-CSF, which is a dimer of 40 Kd. They are usually produced by macrophage and endothelial cells. Their main function is related to cell differentiation and proliferation; they also favor cell maturation. 

Cytokines that stimulate leukocyte chemotaxis.

Chemokines are a group of cytokines, which consists of more than 15 small proteins (7-15 Kd), that are synthesized not only by different immune cells (monocyte-macrophages, T lymphocytes) but also by non immune cells (fibroblasts, endothelial cells) that have a strong chemotactic capability. Their structure is monomeric or dimeric and their membrane receptors have seven trans-membrane domains. 

Depending on their structure and the position of two cysteines, cytokines fall into different groups. 

CYTOKINES of  group a

Those cytokines included in the a group  function mainly as chemotactic,i.e.; recruiting neutrophils and lymphocytes, but not monocytes. The most important cytokines in this group are IL 8 and PAF (platelet activating factor). They are produced by macrophages, lymphocytes, granulocytes, endothelial cells and hepatocytes.  

The b Group consists of cytokines that attract mainly T and B lymphocytes and monocytes. Some cytokines of this group can also recruit basophils and eosinophils. Macrophage inhibiting protein (MIP) and macrophage chemotactic protein (MCP) are chemokines that belong to this group. They are produced by macrophages, T and B lymphocytes and neutrophils. 

CYTOKINES of the group b

CYTOKINES of the group g

The g group  also has chemotactic capability over monocytes and lymphocytes. A representative cytokine of this group is the lymphotactine.