Spontaneous production of interleukin-1 by human alveolar macrophages

A culture system was developed in which human peripheral blood mononuclear cells depleted of monocytes did not proliferate in response to the lectin mitogen phytohemagglutinin (PHA). The response of these cells to PHA was reconstituted with both autologous and heterologous alveolar macrophages. In addition, a partial restoration of PHA responsiveness was seen when the monocyte-depleted cells (MDC) were cultured with supernatants from purified alveolar macrophages, indicating the presence of Interleukin-1 (IL-1) activity in these supernatants. This is the first evidence suggesting the production of IL-1 by tissue macrophages from normal human subjects. In contrast to previous studies of IL-1 production by blood macrophages, it was found to be unnecessary to stimulate the alveolar macrophages in vitro to generate soluble factor activity. It was also found that alveolar macrophages produced active supernatants after only 2 hr in culture, whereas previous studies have indicated that blood monocytes must be cultured for at least 24 hr before active supernatants are produced. These differences may provide evidence that macrophages within the alveolar spaces are in an activated state.