Expression of a single-chain human leukocyte antigen-DRA/DRB3*01:01 molecule and differential binding of a monoclonal antibody in the presence of specifically bound human platelet antigen-1a peptide.

BACKGROUND: Studies show that 1 in 1200 neonates have a low platelet (PLT) count due to alloimmunization against human PLT antigen (HPA)-1a (ß3 -L33). This mainly occurs in HPA-1a-negative mothers who are positive for the human leukocyte antigen (HLA)-DRB3*01:01 allele, but only about one-third of cases will mount an effective alloimmune response. The development of specific treatment modalities requires that the mechanisms driving the maternal alloimmune response against the fetal PLTs be further explored. An antibody reagent that has a different binding affinity to HLA-DRA/DRB3*01:01 with and without the ß3 -L33 peptide would be a valuable reagent to study peptide presentation on maternal antigen-presenting cells. STUDY DESIGN AND METHODS: To identify such antibodies, HLA-DRA/DRB3*01:01 was recombinantly expressed in Drosophila S2 cells. To delineate the epitope of interesting antibodies, seven mutant HLA-DRA/DRB3*01:01 molecules were generated by site-directed mutagenesis introducing naturally occurring amino acid changes encoded by DRB3*02 and DRB3*03 alleles. RESULTS: The murine monoclonal antibody (MoAb) DA2 showed robust binding by enzyme-linked immunosorbent assay to recombinant HLA-DRA/DRB3*01:01, but binding was reduced in the presence of ß3 -L33 peptide. The binding affinity of DA2 to the mutant HLA-DRA/DRB3*0101 in which serine at Position 60 of the ß1-chain was replaced by tyrosine was greatly enhanced. Interestingly the binding of DA2 to the mutant was not reduced by the presence of ß3 -L33 peptide. CONCLUSION: The results of this study generate a molecular model of the interaction of the HLA-DRA/DRB3*01:01 molecule with MoAb DA2. This will inform functional studies with the recombinant Class II molecules.

Heat-transfer resistance measurement method (HTM)-based cell detection at trace levels using a progressive enrichment approach with highly selective cell-binding surface imprints.

Surface-imprinted polymers allow for specific cell detection based on simultaneous recognition of the cell shape, cell size, and cell membrane functionalities by macromolecular cell imprints. In this study, the specificity of detection and the detection sensitivity for target cells within a pool of non-target cells were analyzed for a cell-specific surface-imprinted polymer combined with a heat-transfer-based read-out technique (HTM). A modified Chinese hamster ovarian cell line (CHO-ldlD) was used as a model system on which the transmembrane protein mucin-1 (MUC1) could be excessively expressed and for which the occurrence of MUC1 glycosylation could be controlled. In specific cancer cells, the overexpressed MUC1 protein typically shows an aberrant apical distribution and glycosylation. We show that surface-imprinted polymers discriminate between cell types that (1) only differ in the expression of a specific membrane protein (MUC1) or (2) only differ in the membrane protein being glycosylated or not. Moreover, surface-imprinted polymers of cells carrying different glycoforms of the same membrane protein do target both types of cells. These findings illustrate the high specificity of cell detection that can be reached by the structural imprinting of cells in polymer layers. Competitiveness between target and non-target cells was proven to negatively affect the detection sensitivity of target cells. Furthermore, we show that the detection sensitivity can be increased significantly by repetitively exposing the surface to the sample and eliminating non-specifically bound cells by flushing between consecutive cell exposures.

Development of an on-line high performance liquid chromatography detection system for human cytochrome P450 1A2 inhibitors in extracts of natural products.

An on-line HPLC screening method for detection of inhibitors of human cytochrome P450 1A2 in extracts was developed. HPLC separation of extracts is connected to a continuous methoxyresorufin-O-demethylation (MROD) assay in which recombinant human P450 1A2 converts methoxyresorufin to its fluorescent metabolite resorufin. The system was tested with three P450 1A2 inhibitors, for which minimum detectable amounts (MDA) ranging from 0.7 to 9.5 ng were obtained. Analysis of a kava kava and a basil extract showed that the on-line system is applicable to complex mixtures, since in both extracts, peaks with P450 1A2 inhibiting activity were observed.

Exome sequencing identifies NBEAL2 as the causative gene for gray platelet syndrome.

Gray platelet syndrome (GPS) is a predominantly recessive platelet disorder that is characterized by mild thrombocytopenia with large platelets and a paucity of α-granules; these abnormalities cause mostly moderate but in rare cases severe bleeding. We sequenced the exomes of four unrelated individuals and identified NBEAL2 as the causative gene; it has no previously known function but is a member of a gene family that is involved in granule development. Silencing of nbeal2 in zebrafish abrogated thrombocyte formation.