Prophylaxis or treatment of experimental brucellosis with interleukin-1

Intravenously injected recombinant human interleukin-1 alpha (IL-1α) given to mice 4 h before infection with Brucella abortus 19 depressed the growth of bacteria in the spleen and liver. However, the same dose (10⁵ U) or a 10-fold higher dose was not able to decrease numbers of bacteria when given to chronically infected mice. IL-1 injected into normal mice induced a dramatic increase 2 h later in colony-stimulating activity in serum, measured by bone marrow proliferation, and in colony-stimulating factor 1, measured by radioimmunoassay. Colony-stimulating factor levels declined but remained higher than normal for at least 12 h. The early peak stimulation was not observed in chronically infected mice, but the more prolonged elevation was. As a result of IL-1 treatment, the number of colony-forming cells, especially in the spleen, was increased in normal and acutely or chronically infected mice. Myeloperoxidase staining of newly formed monocytes and polymorphonuclear cells in the spleen revealed an increase in the number of these cells in normal and acutely infected mice as a result of IL-1 treatment, but there was no increase in the already high numbers in chronically infected mice. The relationship between these observations and the basis of chronic infection are discussed.