Human Leucocyte Antigen Sensitisation and Its Impact on Transfusion Practice.

Human leucocyte antigen (HLA) sensitisation, including the formation of antibodies against HLA, can cause serious effects in patients receiving blood. Under certain circumstances, donor HLA antibodies in the blood product can trigger the patient's granulocytes to release mediators that cause transfusion-associated lung injury (TRALI), a serious complication of transfusion. The HLA systems of both donor and patient are involved in transfusion-associated graft-versus-host disease, which is a rare disease with a high mortality. Patient HLA antibodies can destroy incompatible platelets and may cause refractoriness to platelet transfusion. Identification of a patient's HLA antibody specificities is necessary for issuing compatible platelets to overcome refractoriness. Many techniques for the detection and identification of HLA antibodies have been developed, including complement-dependent cytotoxicity assay, bead-based assays, the platelet adhesion immunofluorescence test, and the monoclonal antibody-specific immobilisation of platelet antigens assay. Different strategies for the selection of HLA-compatible platelets are applied. These strategies depend on the breadth of antibody reactivity and range from avoiding single HLA antigens in the platelet concentrates issued to apheresis of platelets from HLA-identical donors. The mechanisms of HLA sensitisation and the efforts made to provide compatible blood products to sensitised patients are reviewed in this article from the perspective of clinical transfusion medicine.

Expression of blood group genes by mesenchymal stem cells.

Incompatible blood group antigens are highly immunogenic and can cause graft rejections. Focusing on distinct carbohydrate- and protein-based membrane structures, defined by blood group antigens, we investigated human bone marrow-derived mesenchymal stem cells (MSCs) cultured in human serum. The presence of H (CD173), ABO, RhD, RhCE, RhAG, Kell, urea transporter type B (SLC14A1, previously known as JK), and Duffy antigen receptor of chemokines (DARC) was evaluated at the levels of genome, transcriptome and antigen. Fucosyltransferase-1 (FUT1), RHCE, KEL, SLC14A1 (JK) and DARC mRNA were transcribed in MSCs. FUT1 mRNA transcription was lost during differentiation. The mRNA transcription of SLC14A1 (JK) decreased during chondrogenic differentiation, while that of DARC increased during adipogenic differentiation. All MSCs synthesized SLC14A1 (JK) but no DARC protein. However, none of the protein antigens tested occurred on the surface, indicating a lack of associated protein function in the membrane. As A and B antigens are neither expressed nor adsorbed, concerns of ABO compatibility with human serum supplements during culture are alleviated. The H antigen expression by GD2dim+ MSCs identified two distinct MSC subpopulations and enabled their isolation. We hypothesize that GD2(dim+) H(+) MSCs retain a better 'stemness'. Because immunogenic blood group antigens are lacking, they cannot affect MSC engraftment in vivo, which is promising for clinical applications.

Alpha-synuclein levels in blood plasma decline with healthy aging.

There is unequivocal evidence that alpha-synuclein plays a pivotal pathophysiological role in neurodegenerative diseases, and in particular in synucleinopathies. These disorders present with a variable extent of cognitive impairment and alpha-synuclein is being explored as a biomarker in CSF, blood serum and plasma. Considering key events of aging that include proteostasis, alpha-synuclein may not only be useful as a marker for differential diagnosis but also for aging per se. To explore this hypothesis, we developed a highly specific ELISA to measure alpha-synuclein. In healthy males plasma alpha-synuclein levels correlated strongly with age, revealing much lower concentrations in older (avg. 58.1 years) compared to younger (avg. 27.6 years) individuals. This difference between the age groups was enhanced after acidification of the plasmas (p<0.0001), possibly reflecting a decrease of alpha-synuclein-antibody complexes or chaperone activity in older individuals. Our results support the concept that alpha-synuclein homeostasis may be impaired early on, possibly due to disturbance of the proteostasis network, a key component of healthy aging. Thus, alpha-synuclein may be a novel biomarker of aging, a factor that should be considered when analyzing its presence in biological specimens.

HLA antibody specification using single-antigen beads--a technical solution for the prozone effect.

BACKGROUND: Substantial progress in human leukocyte antigen antibody specification has been made by the introduction of Luminex single-antigen bead (SAB) assays. This progress was impaired when it turned out that this method is prone to a prozone effect leading to false-negative results in the case of high antibody titers. Testing serum and ethylenediaminetetraacetic acid (EDTA) plasma of one patient in parallel, we observed the prozone effect with the serum sample only. This led us to investigate complement component 1 (C1) as the cause of the prozone in SAB testing. We also found an easy way to overcome the prozone effect. METHODS: Sera with a prozone effect were tested in the SAB assay, applying different methods of serum pretreatment to explore the parameters leading to the prozone. RESULTS: The prozone was not observed when EDTA plasma or serum with EDTA added were tested. Further, addition of dithiothreitol, addition of C1 inhibitor, or heat inactivation of the sera abolished the prozone effect. Adding fresh nonimmune serum to heat-inactivated sera restored the prozone effect. Only beads showing a prozone were found to be covered with C1q. CONCLUSION: Our observations are consistent with the hypothesis that dissociation or destruction of complement C1 eliminates the prozone effect. Addition of EDTA to serum of highly immunized patients is the easiest way to avoid false-negative results in SAB testing caused by a prozone effect.