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

Lipocalins as biochemical markers of disease

Lipocalins as biochemical markers of disease have been used extensively. The clinical indications relate to almost any field of medicine, such as inflammatory disease, cancer, lipid disorders, liver and kidney function. Some of the more well-known lipocalins that have been used as markers of disease are orosomucoid, Protein HC (alpha(1)-microglobulin), apolipoprotein D, retinol-binding protein, complement C8 gamma, prostaglandin D synthase and human tear prealbumin, and these markers will be briefly reviewed in this article. Emphasis, however, will be put on the description of another newly described lipocalin, i.e. human neutrophil lipocalin/neutrophil gelatinase-associated lipocalin (HNL/NGAL), since the body fluid measurement of HNL/NGAL was shown to be a superior means to distinguish between acute viral and bacterial infections and also to accurately reflect the activity and involvement of neutrophils in a variety of other diseases.

Human heart generates complement proteins that are upregulated and activated after myocardial infarction

In human heart, we detected mRNAs and proteins for C1q, C1r, C1s, C2, C3, C4, C5, C6, C7, C8, and C9 with the use of reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemical techniques. We found an upregulation of both mRNAs and proteins in areas of recent and old myocardial infarctions. In both situations, the classical complement pathway was activated, with C4d, C3d, and the membrane attack complex (C5b-9) being deposited on damaged cardiac myocytes. These activated complement components were also identified on Western blots of infarcted tissue. Complement mRNAs in infarcted heart tissue were higher than those in liver, and liver complement mRNAs were not upregulated in cases with infarcted hearts. Our results establish that (1) complement proteins are endogenously produced by human heart; (2) the classical complement pathway is fully activated after myocardial infarction; (3) complement activation is directly involved in myocardial damage after ischemic insults; and (4) damage from complement activation may be chronically sustained. These data suggest that inhibition of the complement system should be effective in treating myocardial infarction.

Characterization of soluble terminal complement complex assembled in C8beta-deficient plasma and serum

Sera genetically deficient in either the alpha-gamma or the beta-subunit of complement component C8 virtually lack haemolytic activity. We have studied the formation and the structural organization of the soluble terminal complement complex (TCC) assembled in these sera following activation with cobra venom factor (CVF). The TCC concentration in the activated C8alpha-gamma and C8beta-deficient samples was 0.2% and 4%, respectively, when compared with zymosan-activated normal serum. TCC was purified from the activated C8beta-deficient samples by affinity chromatography and analysed by immunoblotting and enzyme immunoassay. No C8beta was detected in one TCC preparation, while 7% of the normal level was present in the other. The level of the other terminal components, including that of C8alpha-gamma, was normal. The ability of C8alpha-gamma to promote the assembly of TCC in the presence of a limited amount of C8beta or in the apparent absence of this subunit was confirmed using purified components, by mixing C5b6 and either of the purified C8 subunits together with C7 and C9. These data show that soluble TCC can be formed in C8beta-deficient sera that contain little or no C8beta.

Neurons express proteins of the classical complement pathway in Alzheimer disease

Occurrence of the classical pathway complement proteins C1q, C1r, C1s, C2, C3, C4, C5, C6, C7, C8 and C9 was studied in human hippocampus and temporal cortex by immunohistochemistry and Western blotting. In Alzheimer disease (AD) cases, positive staining for all of these proteins was observed in pyramidal neurons and senile plaques. In control cases, weaker pyramidal neuron staining was observed except for C1q and C1s which were not detected. On Western blots of AD hippocampal extracts, bands corresponding to those detected in normal serum were found for each of the complement proteins. Comparable bands were also detected in normal hippocampal extracts with the exception of C1s which was not observed. The intensity of the bands was generally stronger in AD than in normal extracts, but, in the latter, there was considerable variability between cases and between bands in a single case. These data suggest that pyramidal neurons may be a source of the complement components known to be associated with Alzheimer lesions.

Familial deficiency of the seventh component of complement associated with recurrent meningococcal infections

We describe an 11-year-old girl suffering from recurrent meningitis with a complete absence of the seventh component of complement (C7). Diagnosis was established by haemolytic titration and western blotting. The patient's serum lacked the 85 kDa C7 chain. Haemolytic activity of serum was reconstituted with either pooled normal human serum or with purified C7. The relatives (parents and one sister) had half-normal levels of both immunochemically and functionally determined C7, indicating a heterozygous state for C7 deficiency.

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.