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It was investigated whether the complement dependency of CFUS mobilization observed for certain mobilizing agents is unique for the CFUS compartment, or whether this mobilization reflects a more general mechanism, which involves also the mobilization of mature leukocytes. The number of all recognizable nucleated cell types in the blood was determined following the injection of the mobilizing agents, i.e. endotoxin, zymosan, cobra venom factor, proteinase, trypsin, dextran sulphate and the copolymer of polymethacrylic acid and styrene. The results indicate that if a mobilizing effect of a CFUS mobilizing agent on other nucleated cells occurs, this mobilization of nucleated cells is similarly inhibited or not by C3 to C9 depletion as is observed for the CFUS mobilization. The degree of inhibition is also comparable to the inhibition of CFUS mobilization. The significance of the complement system for the mobilization process is discussed.

A variety of substances can mobilize haemopoietic stem cells (CFUs) into the peripheral blood. In this study the involvement of the complement system in the mobilization process was investigated. Pretreatment of mice with the complement-activating factor of cobra venom (CoF), which lowered the serum C3 levels to 10-25% of the normal value, could completely prevent CFUs mobilization induced by high doses of CoF, endotoxin (ET) from Salmonella typhosa, inulin, zymosan and the proteolytic enzymes proteinase and trypsin. On the other hand, mobilization induced by the polyanions dextran sulphate and the copolymer of polymethacrylic acid and styrene could not be prevented, or at least affected only slightly. There appears to be a relationship between the extent of decomplementation by CoF and the extent of CFUs mobilization induced by ET. The results indicate that certain agents mobilize CFUs via the complement system, whereas other agents induce CFUs mobilization independent of the availability of complement components.

Mobilization of CFUs from haemopoietic tissues into circulation was studied after injection of different bacterial lipopolysaccharides (LPS), zymosan, phytohaemagglutinin (PHA), concanavalin A (Con A), trypsin and di-isopropyl-fluorophosphate-inhibited trypsin. All bacterial LPS used gave an increase of CFUs in the peripheral blood at 1 h after i.v. injection. Some variation in activity could not be excluded. As with Salmonella typhosa LPS, zymosan gave an increase in circulating CFUs during the first few hr and a second peak a few days later. After injection of zymosan as well as S. typhosa LPS the second peak in the blood was accompanied by a large increase in CFUs numbers in the spleen. PHA gave an immediate mobilization of CFUs, but the mobilization after injection of Con A during the first few hr occurred more slowly. After injection of S. typhosa LPS, zymosan and PHA the blood C3 level was found to be depressed considerably. This might indicate that the complement system is involved in the early mobilization of CFUs. Dexamethasone, a synthetic hormone which has been reported to give sequestration of several cell types in the bone marrow, did not inhibit the early and late mobilization of CFUs which normally occurs after injection of S. typhosa LPS.