Beta-2-Microglobulin Synthesis Is Increased during Activation of Human Monocytes

Abstract

We have investigated the regulation of β₂-microglobulin (β₂-M) synthesis by monocytes. Recent interest in β₂-M has developed since the discovery that this protein forms amyloid fibrils in patients undergoing long-term, chronic hemodialysis. The β₂-M amyloid-osis is linked to the greatly elevated levels of monomeric β₂-M in their circulation. Since factors that govern β₂-M release from plasma membranes are not known, we endeavored to evaluate β₂-M release during monocyte activation. Utilizing a human monocyte-like cell line, U937, we studied the effect of bacterial toxin stimulation on levels of membrane, cell surface, and supernatant β₂-M. We now present a novel method to purify β₂-M, a solid-phase radioimmunoassay to measure soluble β₂-M, and an ELISA to measure membrane β₂-M. Using these methods we found that the levels of β₂-M in the cell membrane or on the cell surface did not change during monocyte activation. However, activation did induce a significant increase in the concentration of β₂-M in monocyte supernatants, indicating that β₂-M synthesis by monocytes is increased during monocyte activation. These results suggest that monocyte activation by hemodialysis membranes may be a contributing factor to the observed increase in circulating β₂-M levels.

Hemodialysis-Related Induction of Beta-2-Microglobulin and Interleukin-1 Synthesis and Release by Mononuclear Phagocytes

“…Our data demonstrate that Cuprophan-adherence of monocytes or macrophages is an insufficient stimulus either to activate cells or to increase p2M or IL-1 synthesis or release. In contrast, LPS significantly increases p2M synthesis and release, similar to our previous results with monocyte-like cell line, U937 [32). However, LPS-mediated p2M synthesis by mononuclear phagocytes may be too low to account for the observed increases, i.e.…”

“…The |)2M ELISA utilized anti-|)2M monoclonal lgG [32] that was highly purified by MAPS chromatography (BioRad, Richmond, Calif.), and immobilized in wells of Immunoplates (Nunc, Kamstrup, Denmark), 0.5 pg/well. Human |)2M was purified as de scribed [32] or obtained commercially (Calbiochem Behring, La Jolla, Calif.), a single protein on silver-stained sodium dodecylsulfate polyacrylamide electrophoresis gels, was quantitated by amino acid analysis and by a commercial |TM ELISA kit (Pharmacia Diagnostics).…”

“…Human |)2M was purified as de scribed [32] or obtained commercially (Calbiochem Behring, La Jolla, Calif.), a single protein on silver-stained sodium dodecylsulfate polyacrylamide electrophoresis gels, was quantitated by amino acid analysis and by a commercial |TM ELISA kit (Pharmacia Diagnostics). Our (i2M ELISA is based on competition of sample PjM with biotin-labeled |)2M for entrapment by plate-bound anti-|): M monoclonal antibody.…”

Haemodialysis activates phospholipase A2 enzyme

“…Furthermore amyloid deposits consisting of p 2 -microblobulin in joints and periarticular tissue were described in patients with dialysis arthropathy [58]. The synthesis of pVmicroglobulin might locally be increased by activation of mononuclear cells [59] and by that mechanism favour p 2 -microglobulin amyloid deposition in the presence of a decreased renal clearance of that protein. Thus it is conceivable that repeated PLA 2 activation due to inflammatory effects caused by extracorporeal circulation are relevant for the understanding of some of these signs and symptoms, such as the pathogenesis of dialysis arthropathy.…”

Short-Term Administration of Colchicine to Haemodialysis Patients: Plasma Beta-2-Microglobulin and Phagocyte Oxidative Response

“…As to the daily p2M generation in chronic renal failure, Karlsson et al [3] have found normal synthesis in a limited number of patients. However, the biosynthesis rate of p2M has not yet been accurately determined, and, according to other authors, it could even be actually decreased [4], It is of interest to note that several factors, such as interleukin 1 and tumor necrosis factor, which may be released into the circulation during haemodialysis [5], are able to stimulate p2M production by monocytes (MN) in vitro [6]. There fore, p2M generation could also be increased in dialysis patients intermittently between dialysis sessions.…”