Reduced structural flexibility of eplet amino acids in HLA proteins

International audienceThe proteins encoded in the HLA (Human Leukocyte Antigen) system are largely responsible for the compatibility in organ transplants. To date, the molecular determinants involved in recognizing HLA antigens by recipient antibodies are unknown. Here we explore flexibility as a potential determinant. For this purpose, we compare in terms of N-RMSF (Normalized Root Mean Square Fluctuation) amino acids labeled as confirmed eplets (regions defined around polymorphic amino acids) against amino acids that have not been reported as eplets. We found that eplet amino acids tend to be less flexible than non-eplet amino acids, which would indicate that the antibodies would have a preference for binding with less mobile regions

Relevance of Anti-HLA Antibody Strength Underestimation in Single Antigen Bead Assay for Shared Eplets

International audienceBackground: HLAs contain combinations of multiple eplets, sometimes shared between numerous HLA alleles. Some authors suggested that single antigen bead (SAB) assays may underestimate the signal of anti-HLA antibodies (Ab) when several beads share the targeted eplet. However, this assumption has not yet been validated experimentally.Methods: We selected 5 eplets shared by 1-24 beads of the routine SAB kits: the eplet 163LS/G; the 3 eplets 127K, 62GE, and 62GRN thereafter called cross-reactive group 2C; the 82LR eplet, well-known as Bw4; the locally called QB2A5 eplet associated with the DQA1*05:01/DQB1*02:01 combination; and the 40GR DQ eplet. We selected a dozen of sera for each eplet with Ab mean fluorescence intensity (MFI) between 1000 and 15 000 for the beads carrying the targeted eplet. We tested them with the classical SAB panel (SABp), with an isolated bead carrying the eplet (isolated SAB [SABi]) and with a mixture of both (SABp+i).Results: No significant difference in MFI was detected among SABi, SABp, and SABp+i conditions for all the eplets.Conclusions: We noticed only a nonsignificant difference in the Ab MFI signal due to eplet sharing on the SAB assay. We, therefore, conclude that this phenomenon should no longer be considered as a significant risk factor during patient follow-up pre- or posttransplantation

HLA-EpiCheck : A B-cell epitope prediction tool on HLA antigens using molecular dynamics simulation data

International audienceIn the context of organ transplantation, recipient’s antibodies against donor-specific HLA antigens are the main reason for transplant loss.The prediction of B-cell (antibody) epitopes on HLA antigens is therefore a key challenge on the way to improving the matching stepbetween donor and recipient from a structural point of view. Here, we present HLA-EpiCheck, a B-cell epitope prediction tool that relies onan unprecedented dataset of short Molecular Dynamics (MD) simulations of 207 HLA antigens. We use hydrophobic properties, electrostaticcharges, flexibility and solvent accessibility as descriptors calculated on patches sampled from MD trajectories. Then, we train an ExtremelyRandomized Trees machine learning model. This model outperforms the state-of-the-art DiscoTope 3.0 tool for B-cell epitope predictionon HLA antigens

Importance of Lung Epithelial Injury in COVID-19 Associated Acute Respiratory Distress Syndrome: Value of Plasma sRAGE

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Clinical and Genetic Spectrum of a Large Cohort With Total and Sub-total Complement Deficiencies

International audienceThe complement system is crucial for defense against pathogens and the removal of dying cells or immune complexes. Thus, clinical indications for possible complete complement deficiencies include, among others, recurrent mild or serious bacterial infections as well as autoimmune diseases (AID). The diagnostic approach includes functional activity measurements of the classical (CH50) and alternative pathway (AP50) and the determination of the C3 and C4 levels, followed by the quantitative analysis of individual components or regulators. When biochemical analysis reveals the causal abnormality of the complement deficiency (CD), molecular mechanisms remains frequently undetermined. Here, using direct sequencing analysis of the coding region we report the pathogenic variants spectrum that underlie the total or subtotal complement deficiency in 212 patients. We identified 107 different hemizygous, homozygous, or compound heterozygous pathogenic variants in 14 complement genes [C1Qβ (n = 1), C1r (n = 3), C1s (n = 2), C2 (n = 12), C3 (n = 5), C5 (n = 12), C6 (n = 9), C7 (n = 17), C8 β (n = 7), C9 (n = 3), CFH (n = 7), CFI (n = 18), CFP (n = 10), CFD (n = 2)]. Molecular analysis identified 17 recurrent pathogenic variants in 6 genes (C2, CFH, C5, C6, C7, and C8). More than half of the pathogenic variants identified in unrelated patients were also found in healthy controls from the same geographic area. Our study confirms the strong association of meningococcal infections with terminal pathway deficiency and highlights the risk of pneumococcal and auto-immune diseases in the classical and alternative pathways. Results from this large genetic investigation provide evidence of a restricted number of molecular mechanisms leading to complement deficiency and describe the clinical potential adverse events of anti-complement therapy

First use of imlifidase desensitization in a highly sensitized lung transplant candidate: a case report

International audienceLung transplant candidates who are highly sensitized against human leucocyte antigen present an ongoing challenge with regards to finding immunologically acceptable donors. Desensitization strategies aimed at reducing preformed donor-specific antibodies have a number of limitations. Imlifidase, an IgG-degrading enzyme derived from Streptococcus pyogenes, is a novel agent that has been used to convert positive crossmatches to negative in kidney transplant candidates, allowing transplantation to occur. We present the first case of imlifidase use for antibody depletion in a highly sensitized lung transplant candidate who went on to undergo a successful bilateral lung transplant

Frequency of de novo variants and parental mosaicism in vascular Ehlers–Danlos syndrome

International audiencePurpose: Vascular Ehlers-Danlos syndrome (vEDS) is a rare inherited autosomal dominant disorder caused by COL3A1 pathogenic variants. A high percentage of de novo cases has been suggested. Part of it could be due to parental mosaicism, but its frequency is unknown.Methods: This retrospective study included a large series of COL3A1-confirmed vEDS probands with family information. The frequency of de novo cases was evaluated and the distribution of the type of variants was compared according to the mode of inheritance. The COL3A1 mosaicism was studied by deep targeted next- generation sequencing (NGS) from parental blood DNA.Results: Out of 177 vEDS probands, 90 had a negative family history, suggesting a high rate (50.8%) of de novo pathogenic variants, enriched in the more severe COL3A1 variants (no null variant). Among those, both parental DNA were available in 36 cases and one parental DNA in 18 cases. NGS detected only one mosaicism from maternal blood DNA (allelic ratio 18%), which was confirmed in saliva (allelic ratio 22%).Conclusion: vEDS is characterized by a high frequency of de novo pathogenic variants. Parental mosaicism is rare (2-3%), but should be systematically searched with targeted NGS, taking into account its importance in genetic counseling