Inflammatory response to abdominal irradiation stimulates hemopoiesis

Purpose : The connection between inflammation and hemopoiesis was studied in the context of abdominal irradiation. Materials and methods : Male C57BL6/J mice received localized irradiation of 20 Gy either to 70% of the liver or to the intestine (most of ileum and caecum). Results : Irradiation of liver induced a rapid increase in intercellular adhesion molecule-1 mRNA expression in the liver. In serum/plasma, an increase in positive acute phase proteins (serum amyloid-P and fibrinogen) and a decrease in albumin occurred during the second and third week following liver irradiation. Similarly, intestinal irradiation induced an increase in plasma fibrinogen level. A transient elevation in neutrophil and platelet counts was observed that was maximal during the second and third week with similar kinetics for intestinal and liver irradiation. Moreover, intestinal irradiation enhanced hemopoietic progenitors in bone marrow. IL-6, which is known to be an agonist in the regulation of acute phase protein expression as well as hemopoietic cell production, was increased in plasma from intestinal- and liver-irradiated mice. Administration of an anti-IL-6mAb to intestinal-irradiated mice abrogated the elevation of fibrinogen and the increase in hemopoietic progenitors. Conclusions : Abdominal irradiation provokes an inflammatory response which in turn stimulates hemopoiesis. IL-6 may play a major role in controlling these events.