HUMAN ALVEOLAR MACROPHAGES PRODUCE PREDOMINANTLY THE 35-KD PRO-FORMS OF INTERLEUKIN-1-ALPHA AND INTERLEUKIN-1-BETA WHEN STIMULATED WITH LIPOPOLYSACCHARIDE

Alveolar macrophages (AM) play a key role in local immunoregulation. T he objective of these studies was to compare the production of the pro - and mature forms of both interleukin-1 alpha (IL = 1 alpha) and inte rleukin-1 beta (IL-1 beta) by AM from nine nonsmoking control subjects , six asymptomatic smokers, and nine patients with interstitial lung d isease (ILD). IL-1 alpha and IL-1 beta steady-state mRNA levels in AM cultured over 20 h were determined using specific cDNA probes. IL-1 al pha, 35-kD pro-IL-1 beta, and 17-kD mature IL-1 beta protein levels in cell lysates and supernatants were determined by individual specific ELISAs. Before culture, the isolated AM contained no IL-1 alpha or IL- 1 beta mRNA. AM from nonsmoking control subjects and asymptomatic smok ers produced comparable levels of IL-1 alpha protein, 5.01 +/- 1.02 ng /ml and 4.54 +/- 1.07 ng/ml, respectively, only after stimulation with lipopolysaccharide (LPS) and not with granulocyte-macrophage colony-s timulating factor (GM-CSF). The majority of the IL-1 alpha was present in the cell lysates as 35-kD pro-IL-1 alpha, as determined by Western blot analysis. AM from patients with ILD produced higher levels of LP S-induced cell-associated IL-1 alpha protein (9.78 +/- 1.80 ng/ml, p = 0.031). LPS-induced IL-1 beta production by AM from nonsmoking contro l subjects (5.22 +/- 1.89 ng/ml) and asymptomatic smokers (4.39 +/- 0. 66 ng/ml) was equivalent to total IL-1 alpha protein production. The m ajority of IL-1 beta protein detected was the biologically inactive 35 -kD pro-IL-1 beta in the cell lysate, with a small amount of mature 17 -kD IL-1 beta protein detected in the culture supernatant. AM from pat ients with ILD produced even higher levels of LPS-induced IL-1 beta pr otein, primarily the pro-IL-1 beta species in cell lysates (11.70 +/- 1.90 ng/ml, p = 0.048). The expression of IL-1 alpha and IL-1 beta mRN A correlated with protein production. These data indicate that LPS sti mulation of AM results predominantly in the production of pro-IL-1 alp ha and pro-IL-1 beta. Furthermore, LPS-stimulated AM from patients wit h ILD produce enhanced levels of these cytokines in comparison with AM from control subjects.