IVIG blocks complement deposition mediated by anti-GM1 antibodies in multifocal motor neuropathy.

BACKGROUND: The pathogenesis of multifocal motor neuropathy (MMN) has yet to be established. MMN patients often carry anti-GM1 IgM antibodies, suggesting an autoimmune process involving complement. Intravenous immunoglobulin (IVIG) is the first line treatment, but its action mechanism is unknown. OBJECTIVE: To test whether anti-GM1 IgM antibodies in MMN sera activate complement, inducing and propagating the disease and whether IVIG inhibits complement activation, resulting in clinical improvement. METHODS: Sera with anti-GM1 IgM but not IgG or IgA reactivity were obtained from 13 patients with MMN. We tested whether their anti-GM1 IgM antibodies produced complement component deposits on GM1-coated microtiter plates and whether IVIG blocks such deposition. RESULTS: C1q, C4b, C3b and C5b-9 were deposited on GM1-coated wells. Their depositions were highly correlated with anti-GM1 IgM antibody titre. IVIG reduced the deposition of these complement components dose-dependently. CONCLUSIONS: Anti-GM1 IgM antibodies bound to GM1 and activated complement in vitro. The results together with earlier data from our group suggest that IgM-induced, complement-mediated injury occurs at the nodes of Ranvier in peripheral motor nerves and generates conduction block and muscle weakness. In vitro IVIG inhibited this type of complement activation, suggesting that in vivo, the resulting reduction in membrane attack complex-mediated damage leads to improved muscle strength.

IVIG--mechanisms of action.

Intravenous immunoglobulin (IVIG) preparations are fractionated from a plasma pool of several thousand donors. IVIG contain immune antibodies and physiologic autoantibodies. Immune antibodies reflect the immunologic experience of the donor population. This fraction of IVIG preparations is useful for replacement therapy and passive immunisation. Natural autoantibodies are able to react with the immune system of the recipient of IVIG and are suggested to help to correct immune deregulation. Immunomodulatory and anti-inflammatory properties are based on multiple mechanisms of action which are described. These mechanisms are effective concomitantly and synergistically at every occasion of use of IVIG in inflammatory and autoimmune disorders.

A C3 convertase assay for nephritic factor functional activity.

C3 nephritic factor (C3NeF) is an autoantibody against the C3 convertase which stabilizes this otherwise inherently labile neoenzyme and induces a continuous activation of the alternative pathway with C3 depletion. NeF is found in patients with membranoproliferative glomerulonephritis and/or partial lipodystrpohy. NeF activity is usually detected in plasma by hemolytic tests. In order to obtain reproducible data for the functional activity of purified C3NeF IgG a solid phase assay was developed. C3 convertase was generated on immobilized C3b by incubation with factors B and D in the presence of Ni(2+). Convertase sites were left to decay in the presence of normal IgG or NeF IgG. Residual convertase activity was measured by adding 125I-C3 and capturing nascent 125I-C3b on the plate surface via covalently coupled NH2-Glu-Tyr dipeptide. In the presence of factor H during C3 convertase decay, a dose dependent stabilizing activity was shown for NeF IgG including NeF IgG purified from urine. A second format of the assay was developed in which C3 convertase was assembled on C3b(2)-IgG complexes in the presence of Mg(2+). Since these complexes are more efficient as convertase precursors the signal was five-fold higher than with C3b. Convertase decay, on the other hand, was not influenced by the nature of the precursor and in both systems the stabilizing activity of NeF IgG was similar.

Properdin deficiency in a large Swiss family: identification of a stop codon in the properdin gene, and association of meningococcal disease with lack of the IgG2 allotype marker G2m(n).

Properdin deficiency was demonstrated in three generations of a large Swiss family. The concentration of circulating properdin in affected males was < 0.1 mg/l, indicating properdin deficiency type I. Two of the nine properdin-deficient males in the family had survived meningitis caused by Neisseria meningitidis serogroup B without sequel. Two point mutations were identified when the properdin gene in one of the properdin-deficient individuals was investigated by direct solid-phase sequencing of overlapping polymerase chain reaction (PCR) products. The critical mutation was found at base 2061 in exon 4, where the change of cytosine to thymine had generated the stop codon TGA. The other mutation was positioned at base 827 in intron 3. The stop codon in exon 4 was also demonstrated by standard dideoxy sequencing in three additional family members. The question was asked if genetic factors such as partial C4 deficiency and IgG allotypes could have influenced susceptibility to meningococcal disease in the family. No relationship was found between C4 phenotypes and infection. Interestingly, the two properdin-deficient males with meningitis differed from the other properdin-deficient persons in that they lacked the G2m(n) allotype, a marker known to be associated with poor antibody responses to T-independent antigens. This implies that the consequences of properdin deficiency might partly be determined by independent factors influencing the immune response.

Hypocomplementemic urticarial vasculitis or systemic lupus erythematosus?

The 2 patients presented here showed the typical signs of hypocomplementemic urticarial vasculitis syndrome (HUVS). During follow-up, there was an inverse correlation between anti-C1q autoantibody titer and C1q antigen concentration in serum in both patients over a period of 2 years. The first patient had nephritis characterized by immune deposits in glomeruli and around the tubules. The histological findings, C1q deposits, and presence of tubuloreticular inclusions in capillary endothelial cells suggested a disease process identical to systemic lupus erythematosus (SLE). The second patient, after a lag phase of 2 years, fulfilled a fourth American College of Rheumatology criteria for SLE when she developed anti-double-stranded DNA antibodies. HUVS and SLE overlap, and the criteria for identifying HUVS as an entity distinct from SLE are lacking.

Glomerulonephritis in a patient with complement factor I deficiency.

Complement factor I deficiency is known to be associated with recurrent pyogenic infections. The patient described here had recurrent attacks of otitis, sinusitis, and bronchopneumonia since childhood. At the age of 24 years, he had an acute episode of systemic vasculitis with purpura, but no nephritis. A factor I deficiency was diagnosed when he was 36 years old. Because of the uncontrolled activation of the alternative pathway of complement, several other components were depleted, in particular C3, which explained the predisposition for pyogenic infections. A progressive loss of renal function accompanied by proteinuria and hematuria started after the age of 40 years. Renal biopsy showed a focal segmental glomerulonephritis (GN) with glomerular deposits of immunoglobulins and complement C3 and C4 fragments. The glomerular podocytes showed an almost complete loss of complement receptor 1 (CR1; CD35). The expression of CR1 was very low on erythrocytes, as well. Thus, CR1, the most efficient cell-bound cofactor for the inactivation of C4b/C3b by factor I, appears to be consumed when factor I is missing. Although this is the first report of factor I deficiency associated with GN, it is unlikely that the development of the nephritis was fortuitous because GN has been found in many other diseases characterized by uncontrolled activation of the alternative pathway.

[Hereditary angioedema in the German-speaking region]. / Untersuchungen zum hereditären Angioödem im deutschsprachigen Raum.

A multicentre, retrospective study of hereditary deficiency of C1-esterase inhibitor (C1-INH) function, a deficiency which clinically manifests as hereditary angioedema (HAE), was performed in six centres in Germany, Austria and Switzerland. 242 individuals were registered with proven functional or quantitative deficiency of C1-INH who belonged to kindered with disease manifestation in 2 to 6 generations. Considering the total population in the three countries and the number of registered individuals, a frequency of the deficiency of 0.02 x 10(-4) was calculated. As this epidemiological study involved only 6 centres, a 10 to 100 times higher frequency of C1-INH deficiency is estimated to be a more realistic value. Out of the 242 registered individuals 110 were evaluated for type and location of clinical manifestation of the deficiency, the laboratory data and the therapy outcome. 86 (78.2%) of the patients belonged to the "common type" and 24 (21.8%) to the "variant type" of HAE. In 53.9% of the cases first manifestation of the disease was before the age of 20 years. In only 3.9% of the patient population did the disease begin after 40 years of age. A mean time lag of 5,3 years was observed, between the first manifestation and correct diagnosis. Initial diagnosis was correct in only 31.8% of the cases of which dermatologists provided 51.7%. False diagnoses include urticaria (41.3%), allergy (20%), acute abdomen (18.7%), angina (8%), rheumatoid disease (5.3%) and intracranial haemorrhage, CNS tumour, epilepsy, migraine (5.3%). The distribution pattern of HAE resembled that of intolerance reactions and pseudoallergies. Urticarial lesions were not associated with C1-INH deficiency. 24% of the patients had at least one episode of laryngeal edema. 40% of patients were unable to identify a trigger of edema formation. The others indicated as triggers trauma, hormonal changes, mental stress, insect stings and in a few cases food and drugs. Menstruation and oral contraceptives aggravated or made disease manifestations more frequent. In contrast, during pregnancy in many cases clinical manifestations improved and delivery posed no problems. The possibility of HAO is very much suggested by the tailure of edema to respond to classical anti-allergic therapy. Therapy of choice of acute attacks is C1-INH concentrate. No side reactions, antibody formation or virus transmission have been observed. For long term prophylaxis danazol, an attenuated androgen, or tranexamic acid, a protease inhibitor, was chosen. The daily dose of danazol should be kept as low as possible because of its anabolic, anti-estrogenic, anti-gestagenic, and anti-gonadotropic effects. Indeed, adverse reactions were observed in 41.7% of patients receiving danazol. Frequencies of adverse reactions were twice as common in women as in men. Adverse reactions were dose dependent and reversible except for one woman with irreversible deepening of her voice. Measuring C1r is a effective way to assess C1-INH function and monitor therapy.

Screening for complement deficiency in bacterial meningitis.

Seventy-seven children with bacterial meningitis were screened for complement deficiency. Both the classical and the alternate pathways were normal in 75 patients. Transiently reduced total haemolytic activity of the classical pathway was documented in a boy with meningococcal meningitis. Total haemolytic activity of both the classical and the alternate pathways were reduced in another patient with pneumococcal meningitis: individual complement components determination indicated predominant activation of the alternate pathway.

The human complement C9 gene: identification of two mutations causing deficiency and revision of the gene structure.

The ninth component of human complement (C9) is the last of the terminal complement components creating the membrane attack complex. C9 is a single-chain serum protein that is encoded by a gene located on chromosome 5p. Deficiency of terminal complement components is generally associated with recurrent neisseria infections. We studied a previously described Swiss family with inherited C9 deficiency. To identify the genetic basis of C9 deficiency, we developed an approach using exon-specific PCR and direct DNA sequencing. As a cause of C9 deficiency, we found two different point mutations, both generating TGA stop codons in the coding sequence. One mutation, a C to A exchange, was detected in exon 2 at cDNA position 166, the other, a C to T exchange, was located in exon 4 (cDNA position 464). In family studies of three first-degree relatives with heterozygous C9 deficiency, we demonstrated that the two mutations are segregating independently. Therefore, these mutations are sufficient to explain the complete deficiency of both the probands studied. DNA sequencing of the exon-intron junctions revealed a number of revisions regarding the boundaries between exons 4, 5, and 6 as well as between exons 10 and 11. No additional introns were detected in exons 6 and 10. Furthermore, DNA marker studies were conducted using known polymorphisms of the C6, C7, and C9 genes, confirming the linkage of the observed C9 mutations with defined haplotypes.

Colorectal intussusception: an unusual gastrointestinal complication of hereditary angioedema.

A 21-year-old man with a history of hereditary angioedema presented with protracted abdominal pain which failed to respond to infusion of C1 inhibitor concentrate. Evaluation by CT scan revealed extensive colorectal intussusception requiring surgical intervention. Under replacement therapy with C1 inhibitor concentrate, both the operation under general anesthesia and the postoperative phase were uneventful. The intraoperative examination suggested initiation of intussusception by local mucosal edema in the transverse colon.

High doses of immunoglobulin G attenuate immune aggregate-mediated complement activation by enhancing physiologic cleavage of C3b in C3bn-IgG complexes.

Intravenously applied human IgG has beneficial effects in treating inflammatory diseases, presumably because it has a complement attenuating role. This role of IgG was studied in vitro by following C3 activation and inactivation in sera that were supplemented with exogenous human IgG and incubated with immune aggregates. IgG added at 2 to 10 mg/mL stimulated the physiologic inactivation of C3b-containing complexes twofold to threefold in 20% sera. This, in turn, lowered the overall C3 activation by 28%, as new C3 convertases primarily assembled on C3b-containing complexes. Exogenous IgG (5 mg/mL) also stimulated inactivation of purified C3b2-IgG complexes, whereby their half-life dropped from 3-4 to 1.5 minutes in 20% serum. IgG appeared to act like a modulator of factor H and I because it did not stimulate inactivation of C3b-containing complexes in factor I-deficient serum. Thus, the known partial protection of C3bn-IgG complexes from inactivation by factor H and I was downregulated by high concentrations of IgG. The ability of high doses of IgG to stimulate complement inactivation is a novel regulatory role of IgG. This may be one of the molecular principles for its therapeutic efficacy in treating complement-mediated inflammations.

Genetic detection of the silent allele (*Q0) in hereditary deficiencies of the human complement C6, C7, and C9 components.

DNA polymorphisms (RFLPs) of the human complement component C6, C7, and C9 genes were studied in three C7-deficient (C7D) families, one C6-deficient (C6D) family, and one C9-deficient (C9D) family. The 3 loci are closely linked on human chromosome 5. The haplotypes carrying the "silent" allele (C7*Q0, C6*Q0, and C9*Q0) were defined in each family, allowing for the detection of carriers among asymptomatic relatives. This paper describes familial studies on a type of hereditary trait, characterized by recurrent Neisseria infections in individuals homozygous for "silent" alleles at the C6, C7, or C9 loci.

Fluorescent detection of microsatellite polymorphisms: properdin deficiency linked to PFC microsatellite.

Microsatellite polymorphisms are widely used to map the genes responsible for inherited disorders. The most commonly used detection is based on radioactive labelling and autoradiography. We now present the successful detection of fluorescence-labelled allelic fragments on an automated DNA sequencer. This allows for safer and quicker detection as well as a potential for more efficient processing of the data, e.g. for linkage analysis. The system was tested in the mapping of properdin deficiency, an X-linked condition with increased risk for a severe infection in the affected.

Hereditary complement factor I deficiency.

We describe four cases (from three families) of hereditary factor I deficiency, bringing the total number of cases now reported to 23. In one family there are two affected siblings: one has suffered recurrent pyogenic infections; the other is asymptomatic. In the second family, the patient had recurrent pyogenic infections and a self-limiting vasculitic illness; in the third family, the patient suffered recurrent pyogenic and neisserial infections. All four patients had markedly reduced concentrations of C3 in the serum (family 1 propositus: 28%; family 1 asymptomatic sibling: 15%; family 2: 31%; and family 3: 31% normal human serum) which was in the form of C3b. Low IgG2 levels may occur in primary C3 deficiency, and a reduction in IgG2 concentration to 1.14 g/l (normal: 1.30-5.90 g/l) was found in the patient from family 2. Using radioligand binding assays, we demonstrated increased binding of C3b to erythrocytes in a patient with factor I deficiency. This C3b could not be cleaved by autologous serum but could be cleaved by normal serum or purified factor I. We review and compare the published cases of C3, factor H and factor I deficiency.

Complement profiles in human skin lymph during the course of irritant contact dermatitis.

Using microsurgery a superficial peripheral lymph vessel draining the skin of the upper and medial part of the foot was cannulated on the lower leg of two healthy human volunteers. An irritant contact dermatitis was induced 2 days later by the application of 10% sodium lauryl sulphate to the drained skin area. After a further 3 days the spontaneously regressing skin reaction was treated with clobetasol propionate. Lymph was continuously collected in two aliquots per day for 7 days. The levels of total protein, of albumin and globulins, and of complement components of the classical, the alternative and the lytic pathway as well as the C4A and C4B gene products and the regulatory proteins FB, C1INH, C4BP, FH and FI were determined by ELISA and radial immunodiffusion techniques. Postoperatively, the levels of complement proteins and globulins in the lymph were 5-10 times lower than those in normal human serum, but increased during the course of the skin reaction, while the irritant contact dermatitis did not induce a change in their plasma concentration. In comparison to the baseline, the mean values for C1q, C1r, C2, C5, C6, C7, C8, C9, FB, C1INH, C4BP, FH and FI exhibited a 3-5-fold increase, C3, total C4, albumin and the alpha 1-globulin fraction a 6-9-fold increase, and C1s, C4A, C4B, FB and alpha 2-, beta- and gamma-globulins a 10-20-fold increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating immune complexes in patients with psoriasis: do they exist?

Sera from 16 patients suffering from active psoriasis without arthropathy (2 guttate, 10 nummular, and 4 mixed type) were examined for the presence of circulating immune complexes. Five routine laboratory assay systems were used, based on C1q-binding or detection of IgG-coupled C1q and C3-breakdown products. In 14 patients, no elevated levels of circulating immune complexes were detected. One patient, who additionally suffered from late-phase HIV-1 infection, showed C1q-binding activities as well as levels of IgG-coupled C1q and C3-breakdown products in four of the assay systems, which indicated the presence of immune complexes in his serum. In another patient, with nummular psoriasis, slightly elevated levels of circulating immune complexes were measured by two of the assay systems. These results question the hypothesis of an essential pathogenic role of circulating immune complexes in psoriasis.

Linkage analysis in properdin deficiency families: refined location in proximal Xp.

Properdin is a component of the alternative activation pathway of the complement system. Deficiency or dysfunction of the protein is inherited in an X-linked recessive manner. Affected males have an increased risk of developing meningococcal disease. Six multi-generation families with different types of properdin deficiency were analyzed using microsatellite and other polymorphisms on the X chromosome. Based on multipoint data, it was found that the disease gene maps close to DXS255 (Zmax = 13.3 at theta max = 0.00) and DXS426 (Zmax = 12.9 at theta max = 0.00) on the Xp-arm near the centromere. There was no indication of genetic heterogeneity among the six families analyzed. Thus it is now possible to perform accurate DNA-based determination of the inheritance of the mutation in affected families.