Secreted proteins of human monocytes. Analysis by two-dimensional gel electrophoresis and effect of lipopolysaccharide

Myristyl acylation of the tumor necrosis factor alpha precursor on specific lysine residues

NH2-terminal glycine myristyl acylation is a cotranslational modification that affects both protein localization and function. However, several proteins that lack NH2-terminal glycine residues, including the interleukin 1 (IL-1) precursors, also contain covalently linked myristate. To date, the site(s) of acylation of these proteins has not been determined. During an evaluation of IL-1 acylation, it was observed that [3H]myristate-labeled human monocyte lysates contained a prominent 26-kD myristylated protein, which was identified as the tumor necrosis factor alpha (TNF) precursor protein on the basis of specific immune precipitation. Radioimmunoprecipitates from the supernates of labeled monocytes indicated that the processed or mature 17-kD form of TNF does not contain myristate, suggesting that the site of acylation occurs within the 76-amino acid propiece of the precursor molecule. As the TNF precursor does not contain an NH2-terminal glycine, we hypothesized that myristyl acylation occurs on the N-epsilon-NH2 groups of lysine, of which two are present in the propiece (K19K20). Synthetic peptides were designed to include all seven lysine residues present within the entire 26-kD TNF precursor, and used in an in vitro myristyl acylation assay containing peptide, myristyl-CoA, and monocyte lysate as a source of enzyme. Analysis of reaction products by reverse phase high performance liquid chromatography and gas phase sequencing demonstrated the exclusive myristyl acylation of K19 and K20, consistent with the presence in monocytes of a specific lysyl N-epsilon-NH2-myristyl transferase activity. The acylated lysine residues are located immediately downstream from a hydrophobic, probable membrane-spanning segment of the propiece. Specific myristyl acylation of the TNF propiece may facilitate membrane insertion or anchoring of this critical inflammatory mediator.

The accessory function of B lymphocytes is resistant to the adverse effects of UV radiation

The effect of UV radiation on the accessory activities of B lymphoblastoid cell lines (B-LCL) was investigated in three types of in vitro T lymphocyte proliferation assay, each of which differed in its accessory requirements. In contrast to monocytes whose accessory function was universally sensitive to UV radiation, B-LCL were resistant to UV in oxidative mitogenesis and staphylococcal enterotoxin B assays, in which stimulus processing was not a requirement. Expression of membrane interleukin (IL) 1 and HLA-DR antigens by B-LCL and monocytes was not affected by UV, nor was surface membrane expression of intercellular adhesion molecule-1 (ICAM-1) on B-LCL. These results were in marked contrast to monocytes in which there was a greater than 65% reduction in ICAM-1 expression. When UV-irradiated B-LCL were employed as antigen-presenting cells for tetanus toxoid-dependent T cell stimulation, a reduction in antigen-presenting function was observed. However, pulsing of B-LCL with tetanus toxoid prior to UV irradiation preserved their antigen-presenting capacity in this system also. These findings indicate that there is differential UV sensitivity among accessory cells which may be explained by different effects of UV radiation on antigen processing and adhesion molecule expression.

Productive infection of isolated human alveolar macrophages by respiratory syncytial virus

Respiratory syncytial virus (RSV) is a significant cause of lower respiratory tract disease in children and individuals with cell-mediated immunodeficiencies. Airway epithelial cells may be infected with RSV, but it is unknown whether other cells within the lung permit viral replication. We studied whether human alveolar macrophages supported RSV replication in vitro. Alveolar macrophages exposed to RSV demonstrated expression of RSV fusion gene, which increased in a time-dependent manner and correlated with RSV protein expression. RSV-exposed alveolar macrophages produced and released infectious virus into supernatants for at least 25 d after infection. Viral production per alveolar macrophage declined from 0.053 plaque-forming units (pfu)/cell at 24 h after infection to 0.003 pfu/cell by 10 d after infection and then gradually increased. The capability of alveolar macrophages to support prolonged RSV replication may have a role in the pulmonary response to RSV infection.

Plasma tumor necrosis factor alpha predicts decreased long-term survival in severe alcoholic hepatitis

Plasma tumor necrosis factor alpha (TNF alpha), interleukin 1 alpha (IL-1 alpha), and interleukin 1 beta (IL-1 beta) were measured in plasma samples obtained from 23 patients with severe alcoholic hepatitis on admission and after 30 days of hospitalization. Over a 2-year follow-up period, 14 patients died at a mean time of 8 months following discharge. The presence of elevated plasma TNF alpha either at admission or discharge from the hospital was associated with death in 82% (14/17) of patients. By contrast absence of elevated plasma TNF alpha was associated with survival in 100% (6/6). The difference in survival with and without detectable plasma TNF alpha was significant at p = 0.0022. Plasma TNF alpha was not elevated in alcoholic patients without clinically apparent liver disease, with alcoholic cirrhosis, or in nonalcoholic healthy controls. Plasma IL-1 alpha was also significantly increased in alcoholic hepatitis whereas IL-1 beta was not. Neither IL-1 alpha nor beta was correlated with outcome in the alcoholic hepatitis group. It is concluded that the presence of elevated plasma TNF alpha is a significant predictor of decreased long-term survival in patients with severe alcoholic hepatitis.

Interleukins and tumor necrosis factor in inflammation

Intense research efforts have been directed toward characterizing mediators that control the inflammatory response and regulate the growth, differentiation, and function of cells involved in inflammation. Tumor necrosis factor, or cachectin, and members of a heterogeneous group of peptides called interleukins exhibit a wide spectrum of activities, some of which appear to influence the evolution of inflammatory processes. This review outlines the observations that have led to our current understanding of the biology of tumor necrosis factor and the interleukins. Particular attention is directed toward the evidence suggesting that these cytokines function as mediators of inflammatory responses.