Cobalamin c deficiency associated with antifactor h antibody-associated hemolytic uremic syndrome in a young adult.

BACKGROUND: Thrombotic microangiopathy (TMA) syndromes are characterized by the association of hemolytic anemia, thrombocytopenia and organ injury due to arteriolar and capillary thrombosis. CASE PRESENTATION: We report the first case of adult onset cobalamin C (Cbl C) disease associated with anti-factor H antibody-associated hemolytic uremic syndrome (HUS). A 19-year-old woman was admitted to the nephrology department owing to acute kidney failure, proteinuria, and hemolytic anemia with schizocytes. TMA was diagnosed and plasma exchanges were started in emergency. Exhaustive analyses showed 1) circulating anti factor H antibody and 2) hyperhomocysteinemia, hypomethioninemia and high levels of methylmalonic aciduria pointing towards Clb C disease. Cbl C disease has been confirmed by methylmalonic aciduria and homocystinuria type C protein gene sequencing revealing two heterozygous pathogenic variants. The kidney biopsy showed 1) intraglomerular and intravascular thrombi 2) noticeable thickening of the capillary wall with a duplication aspect of the glomerular basement membrane and a glomerular capillary wall IgM associated with Cbl C disease related TMA. We initiated treatment including hydroxycobalamin, folinic acid, betaine and levocarnitine and Eculizumab. Rituximab infusions were performed allowing a high decrease in anti-factor H antibody rate. Six month after the disease onset, Eculizumab was weaning and vitaminotherapy continued. Outcome was favorable with a dramatic improvement in kidney function. CONCLUSION: TMA with renal involvement can have a complex combination of risk factors including anti-FH autoantibody in the presence of cblC deficiency.

Diagnosis of primary antibody and complement deficiencies in young adults after a first invasive bacterial infection.

OBJECTIVES: Screening for primary immunodeficiencies (PIDs) in adults is recommended after two severe bacterial infections. We aimed to evaluate if screening should be performed after the first invasive infection in young adults. METHODS: Eligible patients were retrospectively identified using hospital discharge and bacteriology databases in three centres during a 3-year period. Eighteen to 40-year-old patients were included if they had experienced an invasive infection with encapsulated bacteria commonly encountered in PIDs (Streptococcus pneumoniae (SP), Neisseria meningitidis (NM), Neisseria gonorrhoeae (NG), Haemophilus influenzae (HI), or group A Streptococcus (GAS)). They were excluded in case of general or local predisposing factors. Immunological explorations and PIDs diagnoses were retrieved from medical records. Serum complement and IgG/A/M testings were systematically proposed at the time of study to patients with previously incomplete PID screening. RESULTS: The study population comprised 38 patients. Thirty-six had experienced a first invasive episode and a PID was diagnosed in seven (19%): two cases of common variable immunodeficiency revealed by SP bacteraemia, one case of idiopathic primary hypogammaglobulinaemia, and two cases of complement (C6 and C7) deficiency revealed by NM meningitis, one case of IgG2/IgG4 subclasses deficiency revealed by GAS bacteraemia, and one case of specific polysaccharide antibody deficiency revealed by HI meningitis. Two patients had previously experienced an invasive infection before the study period: in both cases, a complement deficiency was diagnosed after a second NM meningitis and a second NG bacteraemia, respectively. CONCLUSION: PID screening should be considered after a first unexplained invasive encapsulated-bacterial infection in young adults.

Anti-Factor H autoantibodies in a fifth renal transplant recipient with atypical hemolytic and uremic syndrome.

Hemolytic uremic syndrome (HUS) associated with anti-Factor H (anti-FH) autoantibodies is a recently described pathophysiological entity. Monitoring of anti-FH IgG titer may be a sensitive marker of disease activity and guide treatment to eliminate circulating anti-FH antibodies. We report here a case of atypical HUS (aHUS) in which anti-FH autoantibodies were detected during the course of a fifth kidney transplant, 30 years after the first flare of aHUS. This exceptional case suggests that early, specific management based on immunosuppressive therapy and plasma exchanges monitored by anti-FH IgG titer may result in long-term graft survival.

Melkersson-Rosenthal syndrome and acquired C1 inhibitor deficiency.

BACKGROUND: Melkersson-Rosenthal syndrome (MRS) is a rare disease whose full-blown form is characterized by orofacial swelling, facial palsy and lingua plicata. OBJECTIVE: To investigate the complement system as well as its role in patients with MRS. METHODS: Seven patients presenting at this hospital between November 2002 and May 2003 and meeting the diagnostic criteria according to Hornstein were evaluated retrospectively. The investigations included clinical signs, an analysis of the complement system including levels of CH50, C3, C4, C1 inhibitor (INH) functions and C1-INH antigen detection. RESULTS: Two female patients showed isolated low levels of functional C1-INH as determined by duplicate tests. Both patients took estrogen-progestin contraceptives. CONCLUSION: Since deficiency in plasma protease C1-INH is known to lead to recurrent angioedema, we hypothesize that low levels of functional C1-INH may have contributed to the orofacial swelling in the 2 patients.

Recurrence of hemolytic uremic syndrome after renal transplantation.

Non-Shiga toxin-associated hemolytic uremic syndrome (non-Stx-HUS) is a rare disease. The clinical outcome is often unfavorable: 50% of patients progress to end-stage renal failure. Several mutations in complement regulatory genes predispose to non-Stx-HUS. Transplantation outcomes are poor among patients with either mutation in the genes encoding complement H or I factors, with 80% graft loss due to HUS recurrence. In contrast, patients with mutation in the gene encoding MCP have no disease relapse after transplantation. There are no treatment guidelines for non-Stx-HUS recurrence. Herein we have presented 8 patients with non-Stx-HUS recurrence after transplantation during the last 10 years in the South of France. HUS recurrence, which occurred early after transplantation in all but 1 patient, was treated by plasma exchange (PE) with substitution by fresh frozen plasma (FFP). Three patients still treated with long-term plasma therapy have no recurrence at 15, 19, or 24 months. An international registry would help to define new guidelines.

Recurrence of HUS due to CD46/MCP mutation after renal transplantation: a role for endothelial microchimerism.

Mutations in the gene of the membrane cofactor protein (MCP/CD46), a complement regulatory protein, were recently described as a cause of hemolytic uremic syndrome (HUS). MCP is a transmembrane glycoprotein expressed in kidneys; therefore, the transplantation of a normal kidney should not be complicated by HUS recurrence. However, we report the case of a 32-year-old woman with an MCP mutation who developed a recurrence of HUS after renal transplantation. We found that she had vascular microchimerism of endothelial cells. We suggest that recurrence may be favored by vascular microchimerism, in which the mutated protein is produced in the in the kidney graft by endothelial cells originating from recipient.

Phenotypic expression of factor H mutations in patients with atypical hemolytic uremic syndrome.

We investigated the phenotypic expression of factor H mutations in two patients with atypical hemolytic uremic syndrome (HUS). Factor H in serum was assayed by rocket immunoelectrophoresis, immunoblotting, and double immunodiffusion and in tissue by immunohistochemistry. Functional activity was analyzed by hemolysis of sheep erythrocytes and binding to endothelial cells. A homozygous mutation in complement control protein (CCP) domain 10 of factor H was identified in an adult man who first developed membranoproliferative glomerulonephritis and later HUS. C3 levels were very low. The patient had undetectable factor H levels in serum and a weak factor H 150 kDa band. Double immunodiffusion showed partial antigenic identity with factor H in normal serum owing to the presence of factor H-like protein 1. Strong specific labeling for factor H was detected in glomerular endothelium, mesangium and in glomerular and tubular epithelium as well as in bone marrow cells. A heterozygous mutation in CCP 20 of factor H was found in a girl with HUS. C3 levels were moderately decreased at onset. Factor H levels were normal and a normal 150 kDa band was present. Double immunodiffusion showed antigenic identity with normal factor H. Factor H labeling was minimal in the renal cortex. Factor H dysfunction was demonstrated by increased sheep erythrocyte hemolysis and decreased binding to endothelial cells. In summary, two different factor H mutations associated with HUS were examined: in one, factor H accumulated in cells, and in the other, membrane binding was reduced.

[Acquired C1 inhibitor deficiency associated with lymphoproliferative disorders: four cases]. / Déficit acquis en C1 inhibiteur associé à un syndrome lymphoprolifératif: quatre observations.

INTRODUCTION: Acquired C1 inhibitor deficiency is sometimes associated with lymphoproliferative disorders. EXEGESIS: We report four cases of acquired C1 inhibitor deficiency in association with lymphoproliferative disorders. Three of them were asymptomatic; one was associated with abdominal pain. Four women (median age, 66 years) presented either two non-Hodgkin lymphoma or two chronic lymphocytic leukaemia. C1 inhibitor deficiency was detected fortuitous (n = 1) or during investigation of arthralgia (n = 2), or Gougerot-Sjogren syndrome (n = 1). The deficit was acquired in all cases type I. Auto-immune disorders were associated with: Gougerot-Sjogren syndrome (n = 1), cryoglobulinemia (n = 2), IgM lambda monoclonal gammopathy (n = 1), Coombs positive test (n = 2), IgG anti-cardiolipine antibodies (n = 1). C1 inhibitor deficiency was not modified after lymphoproliferative disorders treatment (radiotherapy, splenic ablation) in two cases but patients were not in complete remission. C1 inhibitor raised normal level in one case, after five chemotherapy regimens, but decreased complement level and C4 split persist. CONCLUSION: Acquired C1 inhibitor deficiency associated with lymphoproliferative disorders is sometimes asymptomatic. Diagnosis could be delay in spite of clinical manifestations. Deficit correction is not constant after lymphoproliferative disorders treatment.

A new type of acquired C1 inhibitor deficiency associated with systemic lupus erythematosus.

Acquired C1 inhibitor (C1-INH) deficiency with consequent angioedema is a rare condition that may indicate an underlying lymphoproliferative disorder. The defect is caused by increased catabolism, which is often associated with the presence of serum autoantibodies to C1-INH. The present report describes 3 patients with systemic lupus erythematosus who developed typical symptoms of acquired angioedema, characterized by recurrent swelling of subcutaneous and mucous tissues. The 3 patients demonstrated a major classical pathway-mediated complement consumption, with very low levels of C3 antigen and decreased levels of C1-INH antigen. Neither antibodies to C1-INH nor associated lymphoproliferative disease was found. No patient had clinical and biologic signs of lupus activity at the time the angioedema occurred. All patients were treated with steroids and exhibited a good response, without relapse of angioedema and with normalization of plasma levels of C1-INH. In lupus patients who present with an angioedema syndrome, acquired or hereditary angioedema must be sought by examining parameters of the classical pathway and levels of C1-INH. Our observations suggest the existence of a new form of acquired C1-INH deficiency associated with a major classical pathway-mediated complement consumption and systemic autoimmunity.

Expression of CD21 is developmentally regulated during thymic maturation of human T lymphocytes.

CD21, the C3d/CD23/Epstein-Barr virus (EBV), receptor is expressed at low density on cells of the T lineage. Immature thymocytes express CD21 with high density. In the present study, we have analyzed the expression of CD21 during intrathymic maturation of T cells. An intense staining for CD21 was observed at the double-negative stage and at the stage of early acquisition of CD4. CD21 expression was decreased at the double-positive and single-positive stages, to then reach levels similar to those of peripheral blood T cells. Staining of thymus sections showed a bright fluorescent signal on thymocytes entering the thymus in the cortical region. Taking advantage of the immature phenotype of cells expressing high amounts of CD21 (CD21(++)), we depleted thymocyte suspensions in CD3(+) and CD8(+) cells to study the properties of CD21 on this cell subset. Triggering of CD21 with its ligands iC3b, CD23 and anti-CD21 mAb did not alter the proliferative response of thymocytes to IL-7, and did not induce the differentiation of early cells into CD4(+)CD8(+) thymocytes. Immunoprecipitation did not reveal any molecule associated with CD21 that could play a signaling role in thymocytes. Finally, EBV induced a down-regulation of CD21 and an up-regulation of CD1 in CD21(++) thymocytes. Taken together, our observations demonstrate a regulated expression of CD21 on human thymocytes and suggest that the CD21(++) subset may be a target for EBV. We further suggest that CD21 on early thymocytes acts as a ligand for CD23-expressing cells in the thymus.

Human lymphocytes shed a soluble form of CD21 (the C3dg/Epstein-Barr virus receptor, CR2) that binds iC3b and CD23.

We report on a soluble (s) form of CD21 (the C3dg/Epstein-Barr virus receptor, CR2) that is spontaneously released by B and T lymphocytes. Immunoprecipitation with anti-CD21 mAb of culture supernatants of surface and biosynthetically labeled B and T cell lines revealed a single band with an apparent molecular mass of 135 kDa. The molecule exhibited a molecular mass 10 kDa lower than that of membrane CD21. The release of soluble CD21 (sCD21) was time dependent and correlated with a parallel decrease in the expression of the membrane-associated molecule. The protein was also found in culture supernatants of tonsillar B cells and normal human thymocytes. Epitopic analysis using combinations of anti-CD21 monoclonal antibodies (mAb) indicated that sCD21 and membrane CD21 were similarly recognized by mAb directed against short consensus repeats (SCR) 1-2, SCR 4-5 and SCR 9-11. Affinity-purified sCD21 was capable of binding to purified human iC3b and to human recombinant CD23, as assessed by enzyme-linked immunosorbent assay and by using the BIAcore technology. In addition, normal human serum was found to contain a soluble form of CD21 that exhibited a similar molecular mass to that of the molecule shed by B and T cells in culture. The serum form of CD21 was recognized by all anti-CD21 mAb that we tested and showed a high reactivity with mAb directed against SCR 1-2. Our observations suggest that B and T cells shed the extracellular portion of CD21 and release a soluble molecule that retains the ligand-binding properties of CD21, thus having a potential role in immunoregulation.