Differential Production of Tumor Necrosis Factor, Macrophage Colony Stimulating Factor, and Interleukin 1 by Human Alveolar Macrophages

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Abstract
Human alveolar macrophages (AMO) have been investigated for their ability to produce three monokines, tumor necrosis factor-alpha (TNF), macrophage colony stimulating factor (CSF-1), and interleukin 1-beta (IL-1). No TNF activity was found in supematants of unstimulated AMO cultured for 20 h, although TNF mRNA was detected in the cells by Northern blot analysis. Stimulation of the cells with lipopolysaccharide (LPS) Induced production and release of high levels of TNF into the culture supernatant. Increased levels of TNF mRNA were detectable at 90 min after LPS stimulation by dot blot analysis, reaching maximum expression between 4 and 8 h and declining thereafter. TNF activity peaked at approximately 8 h in the AMO supematants. After 24 h TNF production had ended. Compared to autologous monocytes the AMO produced 5.7 times more TNF on a per cell basis (activity accumulated in 20 h supematants). Uncultured AMO expressed CSF-1 mRNA which was translated into active protein recovered in supematants upon culture in the absence of stimulus. The addition of LPS to AMO slightly reduced both mRNA levels and amount of factor in the supematants. In contrast to the AMO, monocyte production of CSF-1 was enhanced by LPS. CSF-1 production by AMO continued for at least 48 h of culture. Spontaneous production of low amounts of IL-1 was found in one-third of the AMO samples, while low levels of IL-1 mRNA were present in all tested preparations. LPS stimulation induced increase in IL-1 mRNA within 90 min; mRNA levels peaked between 12 and 20 h and stayed high for at least 42 h. However, while all LPS-stimulated AMO expressed high levels of IL-1 mRNA biologically active IL-1 was again detected only in a fraction of the AMO supematants. These results show that the production of monokines CSF-1, TNF, and IL-1 is differentially regulated by LPS in alveolar macrophages and has different responses as compared to monocytes. The longevity of the messages for each of the factors is possible indicators of the relative contribution of these factors to the response to endotoxin-induced injury and repair processes in the lung.