Studies in vivo and in vitro on an abnormality in the metabolism of C3 in a patient with increased susceptibility to infection
01 Nov 1970-Journal of Clinical Investigation (American Society for Clinical Investigation)-Vol. 49, Iss: 11, pp 1975-1985
TL;DR: Suggestive evidence was presented that the form of C3 with an activated combining site for red cells, previously postulated by others, is a transient C3 conversion product with an electrophoretic mobility slower than that of C 3 on agarose electrophoresis.
Abstract: In a patient with increased susceptibility to infection, lowered serum C3 concentration, and continuously circulating C3b, it was shown that purified 125I-labeled C3 was converted to labeled C3b shortly after intravenous administration. The fractional catabolic rate of C3 was approximately five times normal at 10% of the plasma pool per hr. The synthesis rate and pool distribution of C3 were normal. Despite this evidence of C3 instability in vivo, no accelerated inactivation of C3 was found in vitro. Similarly, no free proteolytic activity could be detected in the patient's serum, and serum concentrations of known protease inhibitors were normal.
Complement-mediated functions, which were markedly deficient in the patient's serum, could be restored partially or completely by the addition of a 5-6S heat-labile beta pseudoglobulin from normal serum. The C3 proinactivator, which has these physicochemical characteristics, was also shown to be either absent or nonfunctional in the patient's serum. An unidentified 6S beta pseudoglobulin to which a monospecific antiserum was available was not detectable in the patient's serum. This last protein appeared not to be a complement component, nor was it the C3 inactivator or proinactivator. Finally, the substance or substances necessary for the conversion of C3b to C3c were missing from the patient's serum.
The administration of 500 ml of normal plasma to the patient corrected all of his abnormalities partially or completely for as long as 17 days. The changes in C3 were dramatic; serum concentration rose from 8 to 70 mg/100 ml, and C3b could no longer be detected. A second metabolic study during this normalization period showed a decrease in fractional catabolic rate toward normal.
The patient's histamine excretion was constantly elevated but increased further after a warm shower and after receiving normal plasma; at both times he had urticaria. These observations were consistent with the endogenous production of C3a and the resulting histamine release from mast cells. The inactivating mechanism for C3a was apparently intact in the patient's serum.
The difference in the electrophoretic mobilities of C3b and C3c was shown as well as the electrophoretic heterogeneity of C3c. Suggestive evidence was also presented that the form of C3 with an activated combining site for red cells, previously postulated by others, is a transient C3 conversion product with an electrophoretic mobility slower than that of C3 on agarose electrophoresis.
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TL;DR: Serum depleted of C3PA had reduced E. coli bactericidal and increased hemolytic activity, and aggregates of immunoglobulins were found to be activating substances, including human IgA, guinea pig γ1, and duck antibody.
Abstract: Evidence has accumulated indicating the existence of a second complement activation mechanism which is functionally analogous to C1, C2, and C4. The noncomplement protein C3PA, previously recognized through its ability to form a complex enzyme with a protein from cobra venom, appears to be the precursor of the C4,2 analogue. It is a thermolabile β-globulin with a molecular weight of 80,000. When serum is treated with naturally occurring plant or bacterial polysaccharides, the C3PA is cleaved into at least two fragments, one having the electrophoretic mobility of a γ-globulin and a molecular weight of 60,000, and the other being an acidic peptide with a molecular weight of 20,000. The larger fragment has the ability to cleave C3 into C3a and C3b and is therefore called C3 activator. It arises from the action of an as yet unidentified serum enzyme upon the C3PA, which is tentatively called C3PA convertase. In addition to endotoxins, yeast cell walls, inulin, and agar, aggregates of immunoglobulins were found to be activating substances, including human IgA, guinea pig γ1, and duck antibody. Serum depleted of C3PA had reduced E. coli bactericidal and increased hemolytic activity. The relationship of the C3-activator system to experimental and clinical observations has been discussed.
765 citations
TL;DR: Electrophoretic studies of fragments from defined types of GBG suggested that GBG cleavage induced by complement or properdin activation in serum occurred through this C moiety, since two variants were detectable in one fragment and two were found in the other fragment.
Abstract: Extensive polymorphism of glycine-rich beta-glycoprotein (GBG) was found in human sera. In all instances, GBG consisted of at least five components on electrophoresis. Patterns were such that they provided evidence for four alleles (at a locus designated Gb) which were expressed as autosomal codominant traits. Gb(S) and Gb(F) were found in all populations but with different frequencies, Gb(F1) was found in Negroes, and Gb(S1) was found in Caucasians. From electrophoretic studies of GBG, evidence was obtained that suggested that the GBG molecule was a tetramer consisting of A and B subunits in a proportion of about 1.6:1. The genetically controlled differences in GBG embodied in the Gb system indicated the presence of a third moiety of the molecule (C), possibly a polypeptide subunit. Electrophoretic studies of fragments from defined types of GBG suggested that GBG cleavage induced by complement or properdin activation in serum occurred through this C moiety, since two variants were detectable in one fragment and two were found in the other fragment. On comparison of fetal-maternal Gb types, approximately one-half the pairs showed differences. This indicated that GBG did not cross the placental barrier.
489 citations
Cites background from "Studies in vivo and in vitro on an ..."
...In a patient with increased susceptibility to infection and congenital hypercatabolism of C3 (17-19), no serum GBG was detectable; properdin activity and properdin Factor B activit 9 were absent despite a normal concentration of properdin protein determined immunochemicatly....
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TL;DR: A large number of these abnormalities are related to Epstein-Barr virus infection, and the use of chemotherapy to correct these problems is a natural progression of disease.
Abstract: Acquired Abnormalities Alterations in the complement system associated with human disease have been appreciated since early in this century,152 but only within recent years have measurements of ser...
329 citations
TL;DR: A patient with striking susceptibility to infection by pyogenic organisms was found to have 1/1000th or less of the normal serum concentration of C3, and it seems that she is homozygous for C3 deficiency.
234 citations
TL;DR: There is evidence that this hyperinflammatory complement phenotype may predispose to accelerated atherosclerosis and also shows an association with Alzheimer's disease, and downregulation of the amplification loop therefore constitutes an important therapeutic target.
Abstract: The C3 amplification loop lies at the core of all the complement pathways, rather than the alternative pathway alone. It is, in evolutionary terms, the oldest part of the complement system and its antecedents can be seen in insects and in echinoderms. The amplification loop is the balance between two competing cycles both acting on C3b: the C3 feedback cycle which enhances amplification and the C3 breakdown cycle which downregulates it. It is solely the balance between their rates of reaction on which amplification depends. The C3 breakdown cycle generates iC3b as its primary reaction product. iC3b, through its reaction with the leukocyte integrins (and complement receptors) CR3 (CD11b/CD18) and CR4 (CD11c/CD18), is the most important mechanism by which complement mediates inflammation. A variety of genetic polymorphisms in components of the amplification loop have been shown to predispose to two kidney diseases—dense deposit disease and atypical haemolytic uraemic syndrome—and to age-related macular degeneration. All predisposing alleles enhance amplification, whereas protective alleles downregulate amplification. This leads to the conclusion that there is a “hyperinflammatory complement phenotype” determined by these polymorphisms. This hyperinflammatory phenotype protects against bacterial infections in early life but in later life is associated with immunopathology. Besides the diseases already mentioned, there is evidence that this hyperinflammatory complement phenotype may predispose to accelerated atherosclerosis and also shows an association with Alzheimer’s disease. Downregulation of the amplification loop therefore constitutes an important therapeutic target.
198 citations
Cites background from "Studies in vivo and in vitro on an ..."
...The final step in working out how the C3b feedback cycle really worked came with the study of a then unique patient, TJ, studied by Chester Alper in Boston (Alper et al., 1970)....
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References
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