Modified Human Beta 2-Microglobulin (desLys(58)) Displays Decreased Affinity for the Heavy Chain of MHC Class I and Induces Nitric Oxide Production and Apoptosis

Beta2-microglobulin (beta 2m) is the light chain of major histocompatibility complex class I (MHC-I) molecules, and is a prerequisite for the binding of peptides to the heavy chain and their presentation to CD8(+) T cells. beta 2m can be modified in vivo and in vitro by proteolytic cleavage by complement C1 and subsequent carboxypeptidase B-like activity - processes that lead to the generation of desLys(58)beta 2m (d beta 2m). This work aims to study the effect of d beta 2m on peptide binding to MHC-I, the influence of d beta 2m on the binding of beta 2m to the MHC-I heavy chain and the biological activity of d beta 2m. Both beta 2m and d beta 2m are able to support the generation of MHC-I/peptide complexes at 18 degrees C, but complexes formed in the presence of d beta 2m destabilize at 37 degrees C. Moreover, a 250 times higher concentration of d beta 2m than of beta 2m is needed to displace MHC-I associated beta 2m from the cell surface. In addition, only beta 2m is able to restore MHC-I/peptide complex formation on acid-treated cells whereas d beta 2m appears to bind preferentially to denatured MHC-I heavy chains. In cell cultures, exogenously added d beta 2m, but not beta 2m, induces apoptotic cell death in monocytic leukaemic cell lines but spares other kinds of leukaemic cells. Additionally, the presence of d beta 2m, and to a lesser extent beta 2m, enhances IFN-gamma-induced NO production by monocytic leukaemic cells. In conclusion, these data show that d beta 2m is not able to support the formation of a stable tri-molecular MHC-I complex at physiological temperature and that d beta 2m exerts other biological functions compared to beta 2m when bound to cells.Danish Medical Research Council; Novo Nordisk Foundation.; Serbian Ministry of Science [143029.

Modified Human Beta 2-Microglobulin (desLys(58)) Displays Decreased Affinity for the Heavy Chain of MHC Class I and Induces Nitric Oxide Production and Apoptosis

Beta2-microglobulin (beta 2m) is the light chain of major histocompatibility complex class I (MHC-I) molecules, and is a prerequisite for the binding of peptides to the heavy chain and their presentation to CD8(+) T cells. beta 2m can be modified in vivo and in vitro by proteolytic cleavage by complement C1 and subsequent carboxypeptidase B-like activity - processes that lead to the generation of desLys(58)beta 2m (d beta 2m). This work aims to study the effect of d beta 2m on peptide binding to MHC-I, the influence of d beta 2m on the binding of beta 2m to the MHC-I heavy chain and the biological activity of d beta 2m. Both beta 2m and d beta 2m are able to support the generation of MHC-I/peptide complexes at 18 degrees C, but complexes formed in the presence of d beta 2m destabilize at 37 degrees C. Moreover, a 250 times higher concentration of d beta 2m than of beta 2m is needed to displace MHC-I associated beta 2m from the cell surface. In addition, only beta 2m is able to restore MHC-I/peptide complex formation on acid-treated cells whereas d beta 2m appears to bind preferentially to denatured MHC-I heavy chains. In cell cultures, exogenously added d beta 2m, but not beta 2m, induces apoptotic cell death in monocytic leukaemic cell lines but spares other kinds of leukaemic cells. Additionally, the presence of d beta 2m, and to a lesser extent beta 2m, enhances IFN-gamma-induced NO production by monocytic leukaemic cells. In conclusion, these data show that d beta 2m is not able to support the formation of a stable tri-molecular MHC-I complex at physiological temperature and that d beta 2m exerts other biological functions compared to beta 2m when bound to cells.Danish Medical Research Council; Novo Nordisk Foundation.; Serbian Ministry of Science [143029.

Associations of circulating cell-free microRNA with vasculopathy and vascular events in systemic lupus erythematosus patients

<p><b>Objective</b>: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a high risk of atherosclerosis and cardiovascular disease (CVD). MicroRNAs (miRNAs) are small non-coding RNAs that modulate protein translation, and dysregulation is seen in autoimmunity, atherosclerosis, and CVD. We investigate associations between circulating miRNAs and markers of atherosclerosis in SLE patients.</p> <p><b>Method</b>: A group (n = 121) of well-characterized SLE patients were screened for atherosclerosis by cardiac computed tomography and carotid ultrasound. RNA was purified from plasma and 46 specific miRNAs were determined using quantitative real-time polymerase chain reaction.</p> <p><b>Results</b>: Forty-one miRNAs were consistently detected. Fifty out of 118 available SLE patients had atherosclerosis. A profile consisting of three miRNAs (decreased miR-125b, miR-101, miR-375) was indicative of atherosclerosis. Multivariate logistic regression identified eight clinical manifestations associated with atherosclerotic outcome. The full classification profile showed a specificity of 88% and a sensitivity of 86%. Hierarchical clustering identified an eight-miRNA profile that differentiated a subgroup of SLE patients (n = 16) who had significantly increased venous thrombotic events (p = 0.045), a higher prevalence of β₂-glycoprotein I antibodies (p = 0.029), and an increased prevalence of thrombocytopenia (p = 0.028).</p> <p><b>Conclusion</b>: In this cross-sectional study, the circulating miRNA profile distinguished SLE patients with atherosclerosis from those without. Furthermore, an eight-miRNA signature was associated with thrombocytopenia, venous thrombotic events, and β₂-glycoprotein I antibodies in SLE patients. Prospective studies are needed to confirm the findings and to establish the precise role of circulating miRNA profiling in the evaluation of atherosclerosis in SLE.</p