Herzyk D J, Allen J N, Marsh C B, Wewers M D
Department of Internal Medicine, Ohio State University, Columbus 43210.
J Immunol. 1992 Nov 1;149(9):3052-8.
Maturation of blood monocytes into macrophages is accompanied by a number of functional changes including decreased IL-1 beta release in response to LPS. This limitation has previously been ascribed to transcriptional regulation. However, in seeming conflict with the observed depression in IL-1 beta mRNA levels, recent work demonstrates increased intracellular IL-1 beta in macrophages. Therefore, the present study sought to explain these differences by comparing IL-1 beta production from autologous alveolar macrophage and blood monocyte pairs at multiple regulatory sites, including endotoxin responsiveness, mRNA expression, protein translation, and post-translational processing. Macrophages did not differ from monocytes in endotoxin sensitivity, but when analyzed by both ELISA and Western blot, were confirmed to have limitations in IL-1 beta release. Gene expression studies demonstrated that at 4 h, macrophage IL-1 beta steady state mRNA levels were 3-fold lower than the monocyte's. However, total IL-1 beta protein production, as measured by [35S]methionine labeling with immunoprecipitation, demonstrated three- to sixfold higher amounts in macrophages at comparable time points. The enhanced protein production in the face of relatively low mRNA levels suggests that macrophages translate IL-1 beta mRNA more efficiently. Furthermore, characterization of IL-1 beta release into supernatants revealed that whereas monocyte release occurred early, represented 5 to 20% of the intracellular amounts, and contained largely processed IL-1 beta, macrophage release was delayed, represented 1 to 5% of the intracellular amounts, and contained primarily unprocessed IL-1 beta. Taken together, these data demonstrate that the limitations in alveolar macrophage IL-1 beta release occur due to slower export and conversion of 35- to 17-kDa protein and are not due to differences in sensitivity to endotoxin or to transcriptional control mechanisms.
血液单核细胞成熟为巨噬细胞的过程伴随着许多功能变化，包括对脂多糖（LPS）反应时白细胞介素-1β（IL-1β）释放减少。这种局限性以前被归因于转录调控。然而，与观察到的IL-1β mRNA水平降低似乎相矛盾的是，最近的研究表明巨噬细胞内的IL-1β增加。因此，本研究试图通过比较来自自体肺泡巨噬细胞和血液单核细胞对在多个调控位点（包括内毒素反应性、mRNA表达、蛋白质翻译和翻译后加工）的IL-1β产生情况来解释这些差异。巨噬细胞在内毒素敏感性方面与单核细胞没有差异，但通过酶联免疫吸附测定（ELISA）和蛋白质印迹法分析时，证实其在IL-1β释放方面存在局限性。基因表达研究表明，在4小时时，巨噬细胞IL-1β稳态mRNA水平比单核细胞低3倍。然而，通过[35S]甲硫氨酸标记免疫沉淀法测定的总IL-1β蛋白产生量表明，在相当的时间点，巨噬细胞中的量高3至6倍。面对相对较低的mRNA水平时蛋白质产生的增强表明巨噬细胞更有效地翻译IL-1β mRNA。此外，对释放到上清液中的IL-1β的特性分析表明，单核细胞的释放发生得早，占细胞内量的5%至20%，并且主要包含加工后的IL-1β，而巨噬细胞的释放延迟，占细胞内量的1%至5%，并且主要包含未加工的IL-1β。综上所述，这些数据表明肺泡巨噬细胞IL-1β释放的局限性是由于35 kDa至17 kDa蛋白的输出和转化较慢，而不是由于对内毒素的敏感性差异或转录控制机制。
