Rôle du complément dans la réponse immunitaire (activation de C3 par le virus de la rougeole et réponse immunitaire adaptative chez un déficit humain en C3)

The complement is a soluble component of the innate immunity, with C3 playing a central role. C3 covalently bind to any activating surface resulting in its permanent labelling. The C3 tag is then recognised by multiple cells of the immune system to ensure increased uptake and co-stimulation of the adaptive immunity. The measles virus (MeV) fusion F protein activates the alternative. The original observation of cold detergent resistant membranes sedimenting at a higher density than the membrane rafts lead us to analyse the respective distribution of F, CD46 and C55 molecules in what we call heavy rafts (HR) and in the classical low density membrane rafts (R). The correlation of F proteins association with HR fraction and the C3b deposition argue for HR-type microdomains to be a site highly favourable for the uncontrolled activation of the alternative pathway in the absence of CD46 and CD55 in close vicinity.A new heterozygous C3 deficit (OMIM 120700) was identified in a 2-year-old male suffering from pyogenic infections with undetectable CH50 and C3 values. The molecular abnormality associate a paternal allele with the missense mutation c.1648T>C (p.Ser550Pro) and an apparently null maternal allele. This C3 deficit is associated with the following defects: low maturation of dendritic cells, lack of circulating memory B cells and inability of CD4 + T cells to differentiate into cTreg type 1LYON1-BU.Sciences (692662101) / SudocSudocFranceF

High-density rafts preferentially host the complement activator measles virus F glycoprotein but not the regulators of complement activation

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Kininogen Cleavage Assay: Diagnostic Assistance for Kinin-Mediated Angioedema Conditions.

Angioedema without wheals (AE) is a symptom characterised by localised episodes of oedema presumably caused by kinin release from kininogen cleavage. It can result from a hereditary deficiency in C1 Inhibitor (C1Inh), but it can present with normal level of C1Inh. These forms are typically difficult to diagnose although enhanced kinin production is suspected or demonstrated in some cases.We wanted to investigate bradykinin overproduction in all AE condition with normal C1Inh, excluding cases with enhanced kinin catabolism, and to propose this parameter as a disease biomarker.We retrospectively investigated high molecular weight kininogen (HK) cleavage pattern, using gel electrophoresis and immunorevelation. Plasma samples were drawn using the same standardised procedure from blood donors or AE patients with normal C1Inh conditions, normal kinin catabolism, and without prophylaxis.Circulating native HK plasma concentrations were similar in the healthy men (interquartile range: 98-175μg/mL, n = 51) and in healthy women (90-176μg/mL, n = 74), while HK cleavage was lower (p14.4% HK cleavage for men; 33.0% HK cleavage for women, with >98% specificity achieved for all parameters. In plasma from patients undergoing recovery two months after oestrogen/progestin combination withdrawal (n = 13) or two weeks after AE attack (n = 2), HK cleavage was not fully restored, suggesting its use as a post-attack assay.As a diagnostic tool, HK cleavage can offer physicians supportive arguments for kinin production in suspected AE cases and improve patient follow-up in clinical trials or prophylactic management

SERPING1 variants and C1-INH biological function : a close relationship with C1-INH-HAE

Hereditary angioedema with C1 Inhibitor deficiency (C1-INH-HAE) is caused by a constellation of variants of the SERPING1 gene (n = 8091,494 pedigrees), accounting for 86.8% of HAE families, showing a pronounced mutagenic liability of SERPING1 and pertaining to 5.6% de novo variants. C1-INH is the major control serpin of the kallikrein–kinin system (KKS). In addition, C1-INH controls complement C1 and plasminogen activation, both systems contributing to inflammation. Recognizing the failed control of C1s protease or KKS provides the diagnosis of C1-INH-HAE. SERPING1 variants usually behave in an autosomal-dominant character with an incomplete penetrance and a low prevalence. A great majority of variants (809/89390.5%) that were introduced into online database have been considered as pathogenic/likely pathogenic. Haploinsufficiency is a common feature in C1-INH-HAE where a dominant-negative variant product impacts the wild-type allele and renders it inactive. Small (36.2%) and large (8.3%) deletions/duplications are common, with exon 4 as the most affected one. Point substitutions with missense variants (32.2%) are of interest for the serpin structure–function relationship. Canonical splice sites can be affected by variants within introns and exons also (14.3%). For noncanonical sequences, exon skipping has been confirmed by splicing analyses of patients\u27 blood-derived RNAs (n = 25). Exonic variants (n = 6) can affect exon splicing. Rare deep-intron variants (n = 6), putatively acting as pseudo-exon activating mutations, have been characterized as pathogenic. Some variants have been characterized as benign/likely benign/of uncertain significance (n = 74). This category includes some homozygous (n = 10) or compound heterozygous variants (n = 11). They are presenting with minor allele frequency (MAF) below 0.00002 (i.e., lower than C1-INH-HAE frequency), and may be quantitatively unable to cause haploinsufficiency. Rare benign variants could contribute as disease modifiers. Gonadal mosaicism in C1-INH-HAE is rare and must be distinguished from a de novo variant. Situations with paternal or maternal disomy have been recorded (n = 3). Genotypes must be interpreted with biological investigation fitting with C1-INH expression and typing. Any SERPING1 variant reminiscent of the dysfunctional phenotype of serpin with multimerization or latency should be identified as serpinopathy

SERPING1 mutation update: Mutation spectrum and C1 Inhibitor phenotypes

International audienceC1 inhibitor (C1Inh) deficiency is responsible for hereditary angioedema (C1-INH-HAE) and caused by variants of the SERPING1/C1INH/C1NH gene. C1Inh is the major control of kallikrein-kinin system. C1Inh deficiency leads to its uncontrolled activation, with subsequent generation of the vasoactive peptide bradykinin. This update documents 748 different SERPING1 variants, including published variants and additional 120 unpublished ones. They were identified as heterozygous variants (n = 729), as homozygous variants in 10 probands and as compound heterozygous variants (nine combinations). Six probands with heterozygous variants exhibited gonadal mosaicism. Probands with heterozygous (n = 72) and homozygous (n = 1) variants were identified as de novo cases. Overall, 58 variants were found at positions showing high residue conservation among serpins, and have been referred to as a mousetrap function of C1Inh: reactive center loop, gate, shutter, breach, and hinge. C1Inh phenotype analysis identified dysfunctional serpin variants with failed serpin-protease association and a residual 105-kDa species after incubation with target protease. Regarding this characteristic, in conditions with low antigenic C1Inh, 74 C1-INH-HAE probands presented with an additional so-called intermediate C1-INH-HAE phenotype. The present update addresses a comprehensive SERPING1 variant spectrum that facilitates genotype-phenotype correlations, highlighting residues of strategic importance for serpin function and for identification of C1Inh deficiency as serpinopathy

Hereditary angioedema with normal C1 Inhibitor associated with Carboxypeptidase N deficiency

International audienceBackground: Hereditary angioedema (HAE) is a potentially life-threatening disordercharacterized by recurrent episodes of subcutaneous or submucosal swelling. HAE withnormal C1 Inhibitor (HAE-nC1-INH) is an under-diagnosed condition. Although theassociation with genetic variants has been identified for some families, the genetic causes inmany patients with HAE-nC1-INH remain unknown. The role of genes associated withbradykinin catabolism is not fully understood.Objective: We investigated the biological parameters and the genes related to kallikrein-kininsystem (KKS) in families with a clinical phenotype of HAE-nC1-INH and presenting with acarboxypeptidase N (CPN) deficiency.Methods: This study includes four families presenting with HAE-nC1-INH and CPNdeficiency. Patients’ clinical records were examined, biological parameters of KKS measured,genetics was analyzed by next-generation sequencing and Sanger sequencing. Predictivealgorithms (HSF®, SIFT®, Polyphen-2®, MutationTaster®, ClinPred®) were used to classifyvariants as affecting splicing, as benign to deleterious, or as disease-causing.Results: Patients presented with angioedema and urticaria, mainly on face/lips, but also withabdominal pain or laryngeal symptoms. Affected patients displayed low CPN activity –30 to50% of median value in plasma. We identified three variants of the CPN1 gene encoding thecatalytic 55-kDa subunit of CPN at: c.533G>A, c.582A>G and c.734C>T. CPN deficiencyassociated with genetic variants segregated with HAE-nC1-INH symptoms in affected familymembers.Conclusions: CPN1 gene variants are associated with CPN deficiency and HAE-nC1-INHsymptoms in four unrelated families. Genetic CPN deficiency may contribute to bradykininand anaphylatoxins accumulation, with synergistic effects in angioedema and urticarialsymptoms

Human C3 deficiency associated with impairments in dendritic cell differentiation, memory B cells, and regulatory T cells.

International audiencePrimary C3 deficiency, a rare autosomal inherited disease (OMIM 120700), was identified in a 2-year-old male suffering from recurrent pyogenic infections from early infancy with undetectable total complement hemolytic activity (CH50) and C3 values. The nonconsanguineous parents and the two patients' two siblings had 50% normal serum C3 concentration. The molecular abnormality associated a paternal allele coding C3 with the missense mutation p.Ser(550)Pro and an apparently null maternal allele, with production of a defective protein that could no longer be secreted. Vaccination of the child did not induce a long-term Ab response. Accordingly, switched memory IgD(-)CD27(+) B cells were barely detected, amounting to only 2.3% of peripheral blood CD19(+) cells. Cells were significantly defective in stimulating alloreactive responses. The in vitro development of immature dendritic cells and their maturation capacity were greatly impaired, with decreased CD1a expression and IL-12p70 secretion ability. These cells were unable to induce autologous B cell proliferation and Ig secretion in the presence of CD40L and C3. Finally, the regulatory T cell development ability of CD4(+) T cells after CD3 and CD46 activation in the presence of IL-2 was significantly impaired. Thus, the association of important functional defects of dendritic cells, acquisition of B cell memory, and regulatory T cells with human C3 deficiency strongly supports a major role for C3 in bridging innate and adaptive immunity in humans

Human C3 deficiency associated with impairments in dendritic cell differentiation, memory B cells, and regulatory T cells.

International audiencePrimary C3 deficiency, a rare autosomal inherited disease (OMIM 120700), was identified in a 2-year-old male suffering from recurrent pyogenic infections from early infancy with undetectable total complement hemolytic activity (CH50) and C3 values. The nonconsanguineous parents and the two patients' two siblings had 50% normal serum C3 concentration. The molecular abnormality associated a paternal allele coding C3 with the missense mutation p.Ser(550)Pro and an apparently null maternal allele, with production of a defective protein that could no longer be secreted. Vaccination of the child did not induce a long-term Ab response. Accordingly, switched memory IgD(-)CD27(+) B cells were barely detected, amounting to only 2.3% of peripheral blood CD19(+) cells. Cells were significantly defective in stimulating alloreactive responses. The in vitro development of immature dendritic cells and their maturation capacity were greatly impaired, with decreased CD1a expression and IL-12p70 secretion ability. These cells were unable to induce autologous B cell proliferation and Ig secretion in the presence of CD40L and C3. Finally, the regulatory T cell development ability of CD4(+) T cells after CD3 and CD46 activation in the presence of IL-2 was significantly impaired. Thus, the association of important functional defects of dendritic cells, acquisition of B cell memory, and regulatory T cells with human C3 deficiency strongly supports a major role for C3 in bridging innate and adaptive immunity in humans