Interleukin-1 beta is an irradiation-induced stromal growth factor

- The blood of irradiated animals contains a growth factor for stromal microenvironment.
- This growth factor is secreted by the bone cells of irradiated animals.
- The expression of Il1b is increased 100-fold in the bone cells of irradiated animals.
- IL-1 stimulates the growth of stromal cells in vitro and in vivo.
- A non-canonical function of IL-1 was revealed.

Gamma irradiation of tissues and organs leads to many pathological consequences due to the formation of reactive oxygen species, DNA damage and the subsequent massive death of cells. The therapeutic use of gamma irradiation in the treatment of cancer is based on its penetrating power and damaging effects on tumor cells. Other effects from the irradiation are unnoticeable in comparison. Moreover, the long-term consequences of gamma irradiation are still poorly understood. When a donor bone marrow plug is implanted under the renal capsule of a syngeneic animal, а hematopoietic ectopic focus is formed. The size of the focus is increased in mice that received irradiation compared to non-irradiated ones, regardless of the amount of time between irradiation and bone marrow plug implantation. Long-term repetitive injections of blood serum from irradiated mice given to syngeneic non-irradiated recipients of bone marrow plugs also lead to the formation of enlarged foci. Hence, the blood of irradiated animals must contain an activity that induces the growth of a hematopoietic microenvironment. It was previously shown that the bones of irradiated animals secrete a growth factor required to create stromal microenvironments. The identity of this factor has, until now, been difficult to obtain. We demonstrated that interleukin 1 beta (IL-1) stimulates the growth of murine bone marrow stromal cells in vitro and in vivo. It was shown that the expression of the Il1b gene and the secretion of its product, IL-1, were activated in bone cells long after total body gamma irradiation. Hence, IL-1, or proteins regulated by this cytokine, appears to be the same stromal growth factor previously observed in the serum of irradiated animals. Our data demonstrate several non-canonical functions of IL-1. In addition, the presence of up-regulated levels of IL-1 long after irradiation points to an unknown mechanism governing its gene expression.