Immunoglobulin and complement studies in children with Schönlein-Henoch Syndrome and other vasculitic diseases

A novel antibody against human properdin inhibits the alternative complement system and specifically detects properdin from blood samples

The complement system is an essential part of the innate immune system by acting as a first line of defense which is stabilized by properdin, the sole known positive regulator of the alternative complement pathway. Dysregulation of complement can promote a diversity of human inflammatory diseases which are treated by complement inhibitors. Here, we generated a novel blocking monoclonal antibody (mAb) against properdin and devised a new diagnostic assay for this important complement regulator. Mouse mAb 1340 specifically detected native properdin from human samples with high avidity. MAb 1340 inhibited specifically the alternative complement mediated cell lysis within a concentration range of 1-10 µg/mL. Thus, in vitro anti-properdin mAb 1340 was up to fifteen times more efficient in blocking the complement system as compared to anti-C5 or anti-Ba antibodies. Computer-assisted modelling suggested a three-dimensional binding epitope in a properdin-C3(H2O)-clusterin complex to be responsible for the inhibition. Recovery of properdin in a newly established sandwich ELISA using mAb 1340 was determined at 80-125% for blood sample dilutions above 1∶50. Reproducibility assays showed a variation below 25% at dilutions less than 1∶1,000. Systemic properdin concentrations of healthy controls and patients with age-related macular degeneration or rheumatic diseases were all in the range of 13-30 µg/mL and did not reveal significant differences. These initial results encourage further investigation into the functional role of properdin in the development, progression and treatment of diseases related to the alternative complement pathway. Thus, mAb 1340 represents a potent properdin inhibitor suitable for further research to understand the exact mechanisms how properdin activates the complement C3-convertase and to determine quantitative levels of properdin in biological samples.

Parvovirus B19 and parvovirus V9 are not associated with Henoch-Schönlein purpura in children

BACKGROUND

Based on single case reports, parvovirus B19 (B19) has repeatedly been proposed as an etiologic agent in patients with Henoch-Schönlein purpura (HSP), perhaps causing vasculitis by direct invasion of vascular endothelial cells because of the tissue distribution of the cellular B19 receptor. A cohort of children with HSP and other vasculitic diseases was investigated and compared with healthy control children to assess the role of B19 as well as parvovirus V9 (a putative emerging B19-like virus).

PATIENTS AND METHODS

Serum samples from 36 children with HSP (n = 29) or other vasculitic diseases (n = 7) were examined, and 38 healthy bone marrow donors were used as controls. The presence of specific B19 and V9 IgM and IgG antibodies was determined with a recently developed enzyme-linked immunosorbent assay, and viral DNA was detected by a novel nested PCR.

RESULTS

Specific IgM was not present in any of the patient or control serum samples. B19 DNA was detected in one patient, a previously healthy 8-year-old boy diagnosed with HSP, whereas none of the controls was B19-positive. V9 was not detected in any of the clinical or control samples. It seems likely that B19 infection might have triggered the development of HSP in the B19-positive patient, because B19 viremia is otherwise uncommon.

CONCLUSIONS

Although causality is difficult to construe in single cases, the data indicate that B19 is not a common contributing factor in the pathogenesis of vasculitis and that this pathogen is only rarely associated temporally with HSP or vasculitic diseases in children.

Platelet function analysis in children with Schönlein-Henoch syndrome

BACKGROUND

Schönlein-Henoch syndrome (SHS) or anaphylactic purpura in childhood is the result of pathologic and immunologic responses to different antigens. These antigens could induce the formation of immune complexes responsible for vasculitis and their precipitation on the endothelium of small blood vessels. Purpuric bruises, hematuria, hematemesis, melena, or hematochesis may suggest coagulation disturbances. Increasing bleeding tendency may suggest platelet function disturbance. To examine the qualitative function of platelets in children with SHS, we decided to analyze its aggregation function.

METHODS

Using the Born method of testing, we analyzed platelet aggregation in 24 children with SHS.

RESULTS

Based on the aggregograms examined, we observed that most patients had abnormal aggregation curves, in which platelets demonstrated a block of release of the endogenous ADP, with or without disaggregation.

CONCLUSIONS

One clinical symptom of SHS appearing in most patients is a mild or increased tendency toward bleeding. On measuring induced aggregation of platelets in children with SHS, we observed that the qualitative function of platelets was disturbed.

Increased transforming growth factor-beta (TGF-beta)-secreting T cells and IgA anti-cardiolipin antibody levels during acute stage of childhood Henoch-Schönlein purpura

Henoch-Schönlein purpura (HSP) is a small vessel vasculitis characterized by increased serum IgA and IgA-dominant immune complex deposition in lesions. The involvement of IgA implies a probable role for TGF-beta, a major factor in IgA production, in the pathogenesis of HSP. Among IgA antibodies, serum IgA anti-cardiolipin antibodies (aCL) have been found in many diseases, including vasculitis. In addition to the clinical presentations and laboratory parameters, we further investigated the roles of IgA aCL and TGF-beta in childhood HSP. Twenty-six Chinese children with the diagnosis of HSP were enrolled. Blood samples from these patients were collected at both acute and convalescent stages. Intracellular staining of lymphocytes was performed to enumerate type 1 (interferon-gamma-secreting), type 2 (IL-4-secreting), and type 3 (TGF-beta-secreting) helper T cells. Serum levels of TGF-beta were detected by ELISA. Serum IgA aCL of 21 of 26 patients at the acute stage, 11 of them at the convalescent stage, were measured by ELISA. The data showed that IgA aCL serum levels were significantly elevated in patients compared with healthy controls (P < 0.001), and those patients at the convalescent stage (P < 0.001). In addition, TGF-beta-secreting T cells were significantly elevated during the acute stage, and decreased at the convalescent stage. Although more studies are needed, the high prevalence of IgA aCL and increased TGF-beta-secreting T cells in children with acute HSP revealed some points which should permit a better understanding of the pathogenesis of HSP.

Complement activation through the lectin pathway in patients with Henoch-Schönlein purpura nephritis

Henoch-Schönlein purpura nephritis (HSPN) is considered a form of systemic vasculitis of the small blood vessels with immune pathogenesis. In this disorder, the complement system is recognized as an important mechanism of glomerular injury. The aim of this study is to determine whether the lectin pathway, a novel pathway of complement activation, is related to the pathogenesis of HSPN. Renal biopsy material from 10 patients with HSPN was studied immunohistochemically and examined for a clinicopathologic correlation. Serum levels of complement components, including mannose-binding lectin (MBL), and plasma levels of complement activation products were also evaluated in these patients and compared with levels in patients with immunoglobulin A (IgA) nephropathy or mesangial proliferative glomerulonephritis (GN) without IgA deposition (non-IgA GN). Glomerular deposition of components of the pathway, MBL and MBL-associated serine protease (MASP-1), as well as C3b/C3c, C5b-9, and C4-binding protein (C4-bp), was detected in 8 of 10 patients. Although no significant correlation was found between glomerular deposition of MBL/MASP-1 and histological or clinical findings, the biopsies on all patients with MBL/MASP-1 deposits were performed within 20 weeks from the onset of disease. Levels of plasma C4d, the activation fragment of C4, and C4-bp, a soluble regulatory protein of the pathway, were greater in patients with HSPN than in those with non-IgA GN. However, there was no difference in serum MBL levels between the three groups of patients (HSPN, IgA nephropathy, and non-IgA GN). These results suggest that complement activation through the lectin pathway was involved at the onset of HSPN, and this mechanism might be important in the disease pathogenesis.

Henoch-Schönlein purpura in children. Report of 100 patients and review of the literature

Henoch-Schönlein purpura (HSP) is an acute leukocytoclastic vasculitis that primarily affects children. In the current report, the author presents the clinical features of 100 children with HSP and reviews the literature, placing particular emphasis on new information concerning the etiology, immunopathogenesis, and treatment of HSP. The dominant clinical features of HSP are cutaneous purpura (100%), arthritis (82%), abdominal pain (63%), gastrointestinal bleeding (33%), and nephritis (40%). The etiology of HSP remains unknown, but it is clear that IgA plays a critical role in the immunopathogenesis of HSP, as evidenced by increased serum IgA concentrations, IgA-containing circulating immune complexes, and IgA deposition in vessel walls and renal mesangium. There are 2 subclasses of IgA, but HSP is associated with abnormalities involving IgA1 exclusively, and not IgA2. This finding may be a consequence of abnormal glycosylation of O-linked oligosaccharides unique to the hinge region of IgA1 molecules. Although several lines of evidence suggest a genetic susceptibility to HSP, the fundamental basis for the abnormalities involving IgA remain unclear. In general, HSP is an acute, self-limited illness, but one-third of patients will have 1 or more recurrences of symptoms. Corticosteroid therapy may hasten the resolution of arthritis and abdominal pain, but does not prevent recurrences. To date, no form of therapy has been shown to shorten appreciably the duration of HSP. The long-term prognosis of HSP is directly dependent on the severity of renal involvement. Corticosteroids in usual doses have no effect on established nephritis. Evidence is emerging that treatment with high-dose intravenous pulse methylprednisolone coupled with azathioprine or cyclophosphamide may be beneficial in patients with severe nephritis.

Is there IgA from gut mucosal origin in the serum of children with Henoch-Schönlein purpura?

Thirty-two children with Henoch-Schönlein purpura with or without renal symptoms were studied to characterize the IgA hyperglobulinemia observed in the serum of most patients. It was shown that only the IgA1 subclass concentration was increased. Secretory IgA and IgA to gliadin levels were frequently increased in serum, with a good correlation between them. Circulating IgA immune complexes were detected often and contained high activity to gliadin. In contrast, IgA activity to tetanus toxoid did not change. We failed to show any differences in renal involvement. These data suggest that elevation of serum IgA in Henoch-Schönlein purpura is due in part to a disturbance of the gut mucosal immune system, and the presence of circulating IgA immune complexes with dietary antigens can be postulated but cannot explain the occurrence of urinary symptoms.

Purpura in infants and children

Hemorrhage into the skin (purpura) may result from abnormalities in any of the three components of hemostasis: platelets, plasma coagulation factors, and blood vessels. The morphology, size, and distribution of the hemorrhagic lesions are helpful diagnostic features. The main causes of purpura in the newborn and the more common hemorrhagic disorders in children are reviewed.

von Willebrand factor and factor XIII in children with Henoch-Schonlein purpura

levels of von Willebrand factor antigen (vWf:Ag) and factor XIII activity (F XIII) were studied in relation to the severity of clinical symptoms (scored from 0 to 3) and to immunological parameters [IgA, C3, C4, and circulating immune complexes (CIC)] in 16 children (7 males, 9 females, aged 3-11 years) with Henoch-Schonlein purpura (HSP) at presentation. vWf:Ag was increased in 7 patients, F XIII activity was decreased in 6. In all children we found high levels of IgA, while C3 and C4 levels were normal; CIC were elevated in 11. vWf:Ag correlated with clinical score and with IgA and CIC, probably as a result of immune-mediated endothelial cell damage. The haemostatic alterations observed in HSP are important for understanding the pathophysiology of the disease.

The absence of anti-neutrophil cytoplasmic antibodies in patients with Henoch-Schönlein purpura

Sera from 14 patients with acute Henoch-Schönlein purpura (HSP) and 5 patients with a past history of HSP were assessed using a immunofluorescence technique for the presence of IgG, IgA, and IgM anti-neutrophil cytoplasmic antibodies (ANCA). There was no evidence of IgG, IgA, or IgM ANCA in the sera of these patients. These results suggest that ANCA are not involved in the pathogenesis of HSP.