[Recurrent meningitis in familial deficiency of the 8th component of the complement system]

Stimulation of mononuclear cells by contact with cuprophan membranes: further increase of beta 2-microglobulin synthesis by activated late complement components

Contact of mononuclear cells (MNC) with cuprophan membranes in vitro causes an increase in beta 2-microglobulin (beta 2m) synthesis. Since in vivo the dialyzer membrane is rapidly coated with plasma proteins, contact activation of MNC was tested in the presence of normal human serum (NHS). After contact with cuprophan, deposition of C5b-9 on the cells was seen, followed by an increase in beta 2m synthesis and cytokine release, exceeding that seen after contact activation in the absence of serum. Inactivated serum or serum deficient in C8 did not increase beta 2m production, indicating that the additional activation was due to complement C5b-9. The results suggest that there are two cuprophan-related mechanisms of cell activation: one by contact of cells with the membrane, the other by the complement activation products. Both might synergistically contribute to an increased beta 2m synthesis in hemodialysis patients.

C5b-8 and C5b-9 modulate the collagen release of human glomerular epithelial cells

Aside from their lytic function the late complement components C5b-9 stimulate release of prostanoids, interleukin 1 and oxygen radicals from a number of cells. Since C5b-9 has also been connected to the development of sclerosis in animal models of glomerulonephritis, we addressed the question whether C5b-9 would affect the collagen synthesis. We used human glomerular epithelial cells (GEC) obtained as primary outgrowth cultures. The cells were cultivated in the presence of 14C-proline. Collagen synthesis was quantitated by counting the radioactivity associated with collagenase digestible material. Furthermore, collagen was analyzed by SDS-PAGE. GEC in culture produce spontaneously some collagen type IV. Addition of sublytic doses of highly purified C5b-9 increased the collagen synthesis considerably within 12 to 24 hours. In the absence of C9, C5b-8 stimulated collagen synthesis to a similar extent, whereas in the absence of C7 or C8, the collagen synthesis was not enhanced. Furthermore, fluid-phase-formed C5b-9 complexes did not stimulate the collagen synthesis, indicating that assembly of the complex on the target membrane was required. Since C5b-9 deposits are found in sclerotic areas, our data support the hypothesis that C5b-9, by stimulating collagen synthesis as well as release, might contribute to the development of chronic nephritis.

Deficiency of the eighth component of complement. Evidence for linkage of C8 alpha-gamma pattern with C8 beta deficiency in sera of twelve patients

The C8 alpha-gamma subunit of the eighth component of complement was analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting in sera from 68 normal individuals, 12 C8 beta-deficient patients (from seven unrelated families), and 10 of the parents of the latter. Three different forms of the C8 alpha-gamma subunit were observed: 34/68 normal individuals were found to have a C8 alpha-gamma triple band (termed C8 alpha-gamma 1, C8 alpha-gamma 2, C8 alpha-gamma 3 variants), 23/68 the C8 alpha-gamma 2 and C8 alpha-gamma 3 variants, and 11/68 the C8 alpha-gamma 1 and C8 alpha-gamma 3 variants. In contrast, all C8 beta-deficient patients had detectable C8 alpha-gamma 2 and C8 alpha-gamma 3 variants but lacked the C8 alpha-gamma 1 variant in addition to the C8 beta subunit. Three out of ten parents of the C8 beta-deficient patients were found to have the C8 alpha-gamma triple band, whereas 7/10, like their children, had the C8 alpha-gamma 2 and C8 alpha-gamma 3 variants only. We conclude that there is a linkage between the C8 alpha-gamma pattern and C8 beta deficiency. These data may support earlier findings that in humans the genes encoding for C8 alpha-gamma and C8 beta are closely linked on chromosome 1.

Immunoblot analysis of the eighth component of human complement. Demonstration of subunits and detection of C8 alpha-gamma double and triple bands

Using SDS-PAGE/immunoblot analysis of the eighth component of human complement, C8, we have been able to demonstrate an 85 kDa C8 alpha-gamma and a 62 kDa C8 beta subunit in normal human serum. Serum from an undiagnosed patient who presented undetectable hemolytic C8 activity possessed only the 85 kDa subunit, suggesting a defect in the C8 beta subunit. Serum of a patient with known C8 alpha-gamma deficiency possessed only the complementary 62 kDa subunit. Both sera used together were able to lyse antibody-sensitized sheep erythrocytes, whereas individual sera could not. Optimum conditions for C8 immunoblotting were determined using small amounts of serum or plasma, during low voltage electrophoresis and a sensitive staining technique (nitrobluetetrazolium/bromochloroindoxylphosphate). Using these conditions, the C8 alpha-gamma subunit was found to be composed of up to three bands, termed C8 alpha-gamma 1, -2 and -3. All three bands were found in pooled normal sera. Individual sera had at least the C8 alpha-gamma 2 and C8 alpha-gamma 3 bands. Two C8 beta-deficient sera from two unrelated patients exhibited only the C8 alpha-gamma 2 and C8 alpha-gamma 3 bands. We conclude that immunoblotting of C8 permits a detailed analysis of the molecular composition of this component and helps to establish a precise diagnosis in inherited C8 deficiencies.