Abstract
In murine spleen cells, x ray irradiation induces the expression of the IL-1β gene at multiple phases of the peak time. We analyzed the immediate-early phase of IL-1β mRNA accumulation. To determine the lineage of cells that showed the immediate response to irradiation, normal spleen cells were analyzed by Northern blotting and in situ hybridization after separation by magnetic antibodies against specific cell-surface antigens. Although most of the spleen macrophages continuously expressed a low level of IL-1β mRNA, a portion of the macrophage population transiently accumulated large amounts of IL-1β message immediately after irradiation. A macrophage-like leukemia cell line that resembles these inducible macro phages was identified. A similar immediate-early and transient increase in the IL-1β mRNA level occurred when cultured spleen cells were irradiated with a low dose (3 Gy) of x rays. In contrast, the x ray-inducible expression of the IL-1β gene was immediate and continuous, not transient, in spleen cells from whole-body irradiated mice. Results of the run-on transcription assay and the determination of the decrease in the message using cultured spleen and macrophage-like leukemia cells indicated that x ray irradiation appears to activate the transcription of the IL-1β gene and partially stabilize the message. The results show that the x ray-induced immediate-early accumulation of IL-1β mRNA is regulated at both the transcriptional and post-transcriptional levels in an as yet unidentified population of spleen macrophages.
