Intracellular localization of human monocyte associated interleukin 1 (IL 1) activity and release of biologically active IL 1 from monocytes by trypsin and plasmin.

Abstract

The production of interleukin (IL 1) by normal human peripheral blood monocytes purified by Ficoll-Hypaque density sedimentation, Percoll-gradient sedimentation, and plastic adherence can be detected as early as 30 min intracellularly, and extracellularly within 1 hr after stimulation with lipopolysaccharide (LPS). Production of mRNA coding for the isoelectric point 7.0 species of IL 1 was also detected as early as 1 hr after LPS stimulation and reached a maximum level at 6 hr. Cell-associated IL 1 activity could be extracted with CHAPS detergent from every cell fraction (i.e., membranes, cytosol, and particulates), but was present mainly (greater than 95%) in the cytosol of LPS-activated monocytes and the myelomonocytic cell line, THP-1. The apparent m.w. of IL 1 activity on high pressure liquid chromatography gel filtration in every cell fraction was approximately 23,000 daltons, with a minor peak at 31,000 daltons, whereas the IL 1 activity in the culture supernatants was 17,000 daltons. Western blotting analysis of LPS-stimulated monocyte extracts showed two forms of IL 1 corresponding to 31,000 daltons and 25,000 daltons. Exposure of viable cells to trypsin and plasmin released biologically active 23,000 dalton IL 1 only from IL 1-producing cells such as activated monocytes and IL 1-producing Ebstein-Barr virus B lymphocyte cell lines. Consequently, biologically active IL 1 is presumably exposed on the outer surface of cell membranes. Furthermore, IL 1 release by human monocytes in plasminogen-depleted fetal calf serum was considerably decreased. Conversely, supplementation of plasminogen-depleted serum with purified plasminogen restored the IL 1 production, suggesting that plasmin or plasmin-like factors may be involved in the regulation of the release of IL 1 from IL 1-producing cells. In conclusion, the results suggest that IL 1 is rapidly produced, is pooled in the cytosol, and in part is processed by enzymes, is transferred to the plasma membranes, and is then released from the cells. Tissue plasminogen activator and serum enzymes such as plasmin may therefore be involved in the release of IL 1 from IL 1-producing cells.