Modulation of granulocyte CSF (G-CSF) receptors on murine peritoneal exudate macrophages (PEM) by various cytokines was investigated. At 4 degrees C, 125I-G-CSF receptor binding on PEM reached a plateau after 6 h and was specifically competed by unlabeled human rG-CSF but not by other cytokines, including human rG-CSF-1, murine recombinant granulocyte-macrophage CSF, murine rIFN-gamma, human rIL-1 beta, and murine rTNF-alpha. 125I-G-CSF bound to PEM has a half-life of 30 min at 37 degrees C. Preincubation of PEM with murine rTNF, murine recombinant granulocyte-macrophage CSF, CSF-1, or G-CSF for 30 min at 37 degrees C resulted in partial reduction of 125I-G-CSF binding capacity, whereas IL-1 or IFN-gamma did not inhibit G-CSF binding. Further studies indicated that reduction of G-CSF binding caused by TNF was a dose- and time-dependent process and did not require FCS. The reduction was transient, and receptor binding was recovered by incubation at 37 degrees C for 8 h. The recovery of G-CSF binding was inhibited in the presence of cycloheximide. In addition, G-CSF binding studies suggested that the TNF-induced decrease in G-CSF binding to PEM was probably due to a reduction in receptor number rather than receptor affinity. Modulation of G-CSFR by TNF was also observed on nonelicited macrophages from various strains of mice. Our results demonstrate a physiologic response of G-CSFR on macrophages that is modulated by TNF. This phenomenon may play an important, as yet unknown, role in the macrophage inflammatory response.