Genetic defects of the complement system

C3 is activated in hereditary angioedema, and C1/C1-inhibitor complexes rise during physical stress in untreated patients

Seven patients with hereditary angioedema (HAE) were studied to understand further how physical exercise may induce attacks. The most pronounced differences between patients and controls, however, were independent of the controlled bicycle run (mean values in patients/ controls); C4(g/L): 0.12/0.28 (P = 0.0122); C4bc (AU/ml): 137.0/18.0 (P = 0.0002); C4d (mg/mL): 5.03/2.35 (P = 0.0004); C3bc (AU/ml): 8.4/6.3 (P = 0.0049); C3a (AU/ml): 11.1/5.6 (P = 0.0102). The ratio C4bc to C4 was 1141 versus 64. Consequently, a substantial part of the low amount of C4 left in HAE patients consists of activation products, and the authors show for the first time that a mild but significant activation of C3 occurs in HAE. The two HAE patients treated with danazol had values of C1-INH function and antigen, C4, and C2 in-between those of normal and untreated patients, and lower levels of split products from C4 and high molecular weight kininogen than untreated patients. As a result of the exercise, fibrinolysis increased significantly in both patients and controls, while C1/C1-INH complexes rose significantly only in the five HAE patients without treatment when compared to the seven controls (P = 0.0089). This study thus suggests that complement activation is enhanced in untreated HAE patients following physical stress.

Effect of time, temperature and additives on a functional assay of C1 inhibitor

There are different recommendations for the handling of blood samples for analyses of the kallikrein-kinin or complement system, respectively. C1 inhibitor (C1-INH) takes a crucial part in both systems. In order to establish recommendations for blood specimen collection and transport for making the diagnosis of hereditary angioedema (HAE), the effect of time, temperature and different additives on C1-INH function and antigen was determined. We used blood samples from normals and patients suffering from HAE type I. Plasma containing EDTA, heparin, sodium citrate or polybrene-EDTA, and serum were assayed after incubations at 4 degrees C or 37 degrees C for 6 or 24 h. In addition, pooled serum was incubated for up to 5 days at room temperature. A modest decrease in C1-INH function was observed as an effect of storage-time in samples from normals (p = 0.039) and a substantial decrease was seen for the HAE patients (p = 0.0002). No significant effect of temperature (4 degrees C or 37 degrees C) was found. Clotting did not reduce C1-INH activity. Plasma containing heparin or polybrene interfered with the functional assay, yielding falsely high and low values, respectively. C1-INH functional assay performed within 24 h in serum, EDTA-treated or citrated plasma discriminated well between HAE patients and normals. This was also the case for serum kept at room temperature for up to 5 days, although a modest fall in C1-INH function was seen in the incubation period. For practical purposes we recommend serum as the sample of choice, preferably received within 48 h.