Induction of interferon-beta and 2',5'-oligoadenylate synthetase mRNAs by interleukin 6 during differentiation of murine myeloid cells

Interleukin 6 (IL 6) induces differentiation of murine myelomonocytic leukemia (M1) cells into mature macrophages. This process is monitored by the sequential appearance of surface markers, induction of intracellular enzymes, and changes in morphology as the cells progress from blast cells to mature macrophages. Differentiation is also associated with growth arrest and accumulation of the differentiating cells in the G0/G1 phase of the cell cycle. Interferon-beta (IFN-beta) is known to be involved in the growth arrest of M1 cells by inducing 2'5'-oligoadenylate synthetase (2',5'-AS). We therefore analyzed whether IL 6 has the potential to trigger the full differentiation program directly or whether its effect on M1 cells is mediated through IFN-beta or through the activation of genes that are typically induced by IFN-beta. We first tested whether IL 6 could induce IFN-beta mRNA. Using a reverse transcription/polymerase chain reaction procedure, we found that IFN-beta mRNA was induced by IL 6. By Northern analysis we determined that IL 6 also caused a significant increase in 2',5'-AS gene expression. IL 6, however, induced the expression of two mRNA species (1.7 and 2.4 kb), whereas IFN-beta mainly induced the expression of the 1.7-kb species. Enhancement of 2',5'-AS gene expression by IL 6 was observed even when protein synthesis was inhibited by cycloheximide. Furthermore, IL 6-induced growth arrest of M1 cells was not inhibited by anti-IFN-beta antibodies. Thus induction of 2',5'-AS gene expression is a primary response to IL-6 and not secondary to the induction of IFN-beta.

Adenosine and its derivatives control human monocyte differentiation into highly accessory cells versus macrophages

Human peripheral blood monocytes have been found to undergo a transitory state of high accessory activity before they fully become macrophages. Time kinetics were done to follow this accessory potential. Studying the regulation of accessory activity, we have found that monocyte-derived accessory cells (m-AC) pass through two phases of development, which both are adversely controlled by cyclic nucleotides. Phase I is positively correlated by intracellular cAMP increase and can be arrested by adenosine 3';5' cyclic monophosphate (cAMP) and synergystic agents. In addition to cAMP, non-cyclic adenine nucleotides and adenosine also mimic all cAMP effects. This behavior is explained by the known presence of surface 5' nucleotidase and adenosine receptor, which in turn leads to activation of adenylate cyclase. At phase II serum is required to convert m-AC into macrophages. In the absence of serum, cells were arrested in the m-AC state. Adenine nucleotides effectively counteract the serum induction leading to the development of m-AC even in the presence of serum. Monocyte/macrophage markers such as Fc receptors and non-specific esterase strictly correlate negatively with the expression of accessory activity. Morphologically, the appearance of veils positively correlates with all experimental situations of high accessory activity. Therefore, it is evident that serum contains regulatory factors that strongly modify the accessory potency of the m-AC via the cyclic nucleotide system, thus presenting a potent immunoregulatory principle at the beginning of the immune cascade.

Veiled accessory cells deduced from monocytes

Human peripheral blood monocytes were cultured under conditions which prevent macrophage development. Media containing selected charges of fetal calf serum as well as a number of serum-free and protein-free media were found to convert monocytes into homogenous populations of loosely adherent veiled cells. After one week of culture, these cells developed dendritiform elongations. Functionally, these cells acquired an increased capability of serving as accessory cells in T lymphocyte mitogenic stimulation. Phenotypically, they were strongly reduced in macrophage markers such as nonspecific esterase, phagocytosis and Fc-receptors. The majority of the population was even negative for these markers. It thus appears that highly active accessory cells, which closely approach the phenotype of lymphoid dendritic cells, could be deduced from monocytes. These accessory cells could be maintained in culture for several weeks without proliferation and without converting to macrophages. They could further be induced to differentiate to macrophages by an activity present in human serum. Ontogenetically, the accessory state as described here is a differentiation stage preceding macrophage differentiation. When macrophages differentiate from monocytes, they have to pass the transient stage of increased accessory activity.