A single low dose of human recombinant interleukin 1 accelerates the recovery of neutrophils in mice with cyclophosphamide-induced neutropenia.

The actions of the cytokine interleukin 1 (IL-1) in hematopoiesis involve induction of colony-stimulating factor (CSF) production on accessory cells in the hematopoietic microenvironment and synergy with CSF on early hematopoietic progenitor cells. We have used these properties to accelerate hematologic reconstitution in granulocytopenic mice. Mice with cyclophosphamide-induced granulocytopenia were injected i.p. at day 0 with a single dose (8-800 ng) of human recombinant IL-1 alpha. At daily intervals thereafter during a period of 7 days mice were sacrificed and blood granulocytes and bone marrow cellularity were assessed. Mice receiving a single dose of 80 or 800 ng IL-1 had significantly (p less than 0.05) higher blood granulocyte counts at days 4 and 5 than control animals receiving heat-activated IL-1. This activity of IL-1 was not affected by injection of the cyclooxygenase inhibitor ibuprofen. Bone marrow cellularity, as assessed in histological sections of femurs, was significantly greater (p less than 0.05) at day 2 in mice treated with 80 or 800 ng IL-1. These results show that a single low dose of IL-1 may be used to accelerate the reconstitution of granulocytes following granulocytopenia induced with chemotherapy.