[Cytokines and hematopoiesis]

In hematopoiesis, regulation and differentiation present a very complex functional network in which multiple factors of the microenvironment are involved. In addition to direct cell-to-cell contacts and the modifying influences of the intercellular matrix, soluble mediators play an important role in intercellular communication. Cytokines exert their effects by binding with specific receptors that transfer their signals to individual cells. A common structure shared by subunits of these receptors leads to competitive inhibition in binding the cytokines with different affinity. By this mechanism specificity is reduced, on the one hand; however, on the other the complexity of interactions in the bone marrow is enhanced. A flood of in vitro and in vivo studies have established the impact of various cytokines on single hematopoietic cell lineages and their application for clinical use. However, there is a lack of knowledge concerning the cellular origin of the cytokines. According to the results of our studies elements of the erythro- and megakaryopoiesis are the source of cytokines like IL-1 alpha, IL-3, IL-6, and GM-CSF.