Abstract
Earlier studies suggested the existence of a blood-bone marrow barrier that significantly inhibits the transfer of plasma macrophage colony- stimulating factor (M-CSF) to responsive hematopoietic cells in vivo as indicated by its failure to induce a receptor downregulation in bone marrow cells. In this study, the effect of recombinant human interleukin-1 (rhuIL-1) was investigated. In vivo administration of rhuIL-1, either intraperitoneally (IP) or intravenously (IV), induced a rapid transient loss of M-CSF receptor binding activity in bone marrow cells, with a nadir occurring between 2 to 4 hours while loss of M-CSF receptors by cells in the peritoneal cavity occurred only in animals receiving rhuIL-1 via IP administration. The loss of M-CSF receptor activity after rhuIL-1 treatment was correlated with an elevated level of circulating M-CSF. However, the loss of M-CSF receptors in marrow cells was prevented by dexamethasone (Dex) treatment before rhuIL-1 administration. The fact that Dex treatment also reduced the level of circulating M-CSF after rhuIL-1 administration suggests that the inhibitory effects of IL-1 are mediated through locally produced M-CSF. Administration of rhuM-CSF at higher doses, either IV or IP, also induced a loss of M-CSF receptor of lesser degree in the marrow cells. However, the loss of M-CSF receptors by the peritoneal cells was induced only in mice receiving rhuM-CSF through IP administration. Taken together, these results indicate the existence of a unidirectional barrier that prevents the transfer of blood M-CSF and IL- 1 to peritoneal cavity but not vice versa.
