Complement receptor expression of primates and non-primates detected by the rosette formation technique

Current status of ctDNA in precision oncology for hepatocellular carcinoma

The conventional method used to obtain a tumor biopsy for hepatocellular carcinoma (HCC) is invasive and does not evaluate dynamic cancer progression or assess tumor heterogeneity. It is thus imperative to create a novel non-invasive diagnostic technique for improvement in cancer screening, diagnosis, treatment selection, response assessment, and predicting prognosis for HCC. Circulating tumor DNA (ctDNA) is a non-invasive liquid biopsy method that reveals cancer-specific genetic and epigenetic aberrations. Owing to the development of technology in next-generation sequencing and PCR-based assays, the detection and quantification of ctDNA have greatly improved. In this publication, we provide an overview of current technologies used to detect ctDNA, the ctDNA markers utilized, and recent advances regarding the multiple clinical applications in the field of precision medicine for HCC.

A complement receptor for opsonized immune complexes on erythrocytes from Oncorhynchus mykiss but not Ictalarus punctatus

Immune complexes activate the classical pathway of complement resulting in the covalent deposition of fragments of the third (C3b) and fourth (C4b) components of complement, thus opsonizing the complexes for uptake by CD35 found on human erythrocytes. The complexes are then transported to and cleared from the circulation by the reticuloendothelial system. It has been shown that rainbow trout can remove immune complexes from the circulation in a complement-dependent manner similar to that found in the human. However, the cell or cell types involved have not been identified. The purpose of this study was to investigate whether a complement-dependent immune adherence receptor is expressed on erythrocytes from the rainbow trout (Oncorhynchus mykiss) and the channel catfish (Ictalarus punctatus). Coating fluorescent microparticles with BSA, and then binding them to anti-BSA created an artificial immune complex that was incubated with normal fish serum, normal human serum or EDTA-treated serum. The complement-coated immune complexes were then incubated with either fish or human erythrocytes and analyzed for binding by flow cytometry and further visualized by fluorescence microscopy. Our results indicate that erythrocytes from rainbow trout are capable of binding immune complexes when pretreated with serum from either the trout or human, but not when pretreated with serum containing EDTA. By contrast, erythrocytes from the channel catfish did not bind immune complexes pretreated with autologous or human serum. These data suggest that differences exist in receptor distribution between two closely related species of fish, and a potentially homologous relationship in receptor expression, and possibility function, exist between two highly divergent species.

Complement Factor H Limits Immune Complex Deposition and Prevents Inflammation and Scarring in Glomeruli of Mice with Chronic Serum Sickness

Factor H is the major complement regulator in plasma. Abnormalities in factor H have been implicated in membranoproliferative glomerulonephritis in both humans and experimental animals. It has been shown that factor H on rodent platelets functions analogously to human erythrocyte complement receptor 1 in its role to traffic immune complexes to the mononuclear phagocyte system. C57BL/6 factor H-deficient mice (Cfh(-/-)) and wild-type (wt) controls were immunized daily for 5 wk with heterologous apoferritin to study the chronic serum sickness GN model. Immunizations were started in 6- to 8-wk-old mice, which was before the development of spontaneous membranoproliferative glomerulonephritis in some Cfh(-/-) animals. Glomerular deposition of IgG immune complexes in glomeruli was qualitatively and quantitatively increased in Cfh(-/-) mice compared with wt mice. Consistent with the increase in glomerular immune complexes and possibly because of alternative pathway complement activation, Cfh(-/-) mice had increased glomerular C3 deposition. Wt mice developed no glomerular pathology. In contrast, Cfh(-/-) mice developed diffuse proliferative GN with focal crescents and glomerulosclerosis. In addition, there was significantly increased expression of collagen IV, fibronectin, and laminin mRNA in Cfh(-/-) glomeruli. These data show a role for platelet-associated factor H to process immune complexes and limit their accumulation in glomeruli. Once deposited in glomeruli, excessive complement activation can lead to glomerular inflammation and the rapid development of a scarring phenotype.

A protein with characteristics of factor H is present on rodent platelets and functions as the immune adherence receptor

Complement-coated particles interact with specific immune adherence receptors (IAR). In primates, this function is served by complement receptor 1 (CR1) on erythrocytes. In contrast, rodent platelets bear IAR distinct from CR1, the identity of which was studied here. A 150-kDa C3b-binding protein was isolated from rat platelets, which had immunochemical and biochemical identity to plasma factor H. Immunofluorescence microscopy and flow cytometry demonstrated that factor H was present on the surface of rat and mouse platelets, which could be removed by treatment with neuraminidase. Sheep erythrocytes bearing C3b underwent immune adherence with rat and mouse platelets, which was blocked with anti-factor H F(ab')(2) antibodies, but not with antibodies binding to the complement regulator, Crry, on the platelet surface. By reverse transcription-polymerase chain reaction using rat platelet RNA and primers designed from mouse factor H, a 472-base pair product was generated that was identical in sequence to that produced from rat liver RNA. The translated protein product was 85% similar to mouse liver factor H. The 3'-nucleotide sequence from platelets predicted a soluble factor H protein. By Northern analysis, liver and platelets had identically sized factor H mRNA. Thus, rat and mouse platelets have a membrane protein with characteristics of factor H that is linked via sialic acid residues and functions as the IAR. Whether platelet factor H is acquired by passive adsorption from sera and/or is produced by platelets remains to be determined.

Leishmania immune adherence reaction in vertebrates

In normal human blood, C3-opsonized Leishmania promastigotes immune adhere to erythrocytes, a mechanism believed to enhance their clearance from blood and phagocytosis. Given the potential importance of this reaction in host defence against infection, the promastigote-erythrocyte interaction was studied in blood of individuals from one avian and 12 mammalian genera; [111In]-labelled promastigotes were found to bind only to primate erythrocytes. Nevertheless, previous experiments coincubating platelets isolated from nonprimate mammals with C3-opsonized promastigotes led to promastigote-platelet adherence. To ascertain whether this is a natural mechanism in nonprimate Leishmania infection, normal blood from members of Leishmania animal models of interest, dog, guinea-pig, hamster, mouse and rabbit, was infected ex vivo with promastigotes. Within 1 min of blood contact, the promastigote surface was loaded with platelets, rapidly evolving into large aggregates. These results confirm the physiological nature of the reaction and demonstrate that promastigote-erythrocyte and promastigote-platelet binding are the first parasite-host cell encounters after Leishmania invasion of primates and nonprimate mammals, respectively. Leishmania immune adherence shares the characteristics of the nonanticipatory immune systems, and we consider it should be viewed as an innate vertebrate host effector mechanism.

Regulatory system of guinea-pig complement C3b: two factor I-cofactor proteins on guinea-pig peritoneal granulocytes

Complement factor I is a plasma protease serving for proteolytic inactivation of C3b together with its cofactor. We have identified two factor I-cofactor activities in solubilized extracts of guinea-pig peritoneal granulocytes using guinea-pig factor I (Igp) and fluorescent-labeled methylamine-treated guinea-pig C3 (f-C3(MA)gp). One of these eluted from a chromatofocusing column between pH 7.6-7.1, and the other at about pH 5.7. These two cofactor fractions both interacted with Igp and, to a lesser degree, with human factor I (Ihu) on C3(MA)gp cleaving it into an inactive C3bi analogue, but did not cleave methylamine-treated human C3 (C3(MA)hu) together with Igp or Ihu. These factors are therefore species specific. The neutral and acidic fractions with cofactor activity contained C3(MA)gp-binding proteins with a doublet of 55 kDa and 42 kDa, and a singlet of 160 kDa, respectively, on SDS-PAGE. These proteins may be membrane cofactor protein (MCP) and C3b/C4b receptor (CR1) of guinea-pigs.

Effects of age, sex, and psychological disturbance on immunoglobulin levels in the squirrel monkey

The following research assessed the influence of developmental, hormonal, and psychological factors on immunoglobulin and complement protein levels in the squirrel monkey. A cross-sectional life span study established that the developmental pattern of immunoglobulins and complement proteins was similar to that observed in humans. IgG and IgM levels rose progressively with age, while the complement system was mature at birth. In contrast to humans, this species showed a significant sex difference in IgG levels, with higher levels in males during both infancy and adulthood. Males also showed a greater antibody response to viral challenge than did females, and evaluation of gonadectomized subjects suggested that the sex difference in antibody production was testosterone-dependent. The effect of acute and sustained psychological disturbance on IgG levels was also evaluated in infant monkeys. Repeated, brief separations from the mother did not alter IgG levels, but IgG levels were suppressed after a 7-day removal from the mother. Therefore, despite the general view that immunoglobulin levels are relatively stable, these studies have established that immunoglobulin levels can be strongly influenced by hormonal and experiential factors in the squirrel monkey.

Isolation of decay-accelerating factor (DAF) from rabbit erythrocyte membranes

A regulatory protein purified from rabbit erythrocyte stroma had decay-accelerating activity to C5 convertases on hemolytic intermediate cells (EAC1-3b, P). Its molecular weight was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing conditions to be 66,000, slightly smaller than that of human decay-accelerating factor (DAF). The amino acid composition of the protein resembled that of human DAF. The protein was incorporated into sheep erythrocytes. The incorporation and the decay-accelerating activity were inhibited by low density lipoprotein. It did not bind to rabbit C3-Sepharose in a column under conditions in which human CR1 bound, but its interaction with rabbit C3 was evident from the retardation of its elution from the column. These results indicate that the protein purified from rabbit erythrocyte stroma was DAF.

Marmoset red blood cell receptor for membrane-associated complement components is not related to human CR1: partial characterization of the C3-binding proteins responsible for the spontaneous rosette formation between marmoset red blood cells and human leukocytes

Cells from all the human B-lymphoblastoid cell lines tested and most human monocytes form rosettes with marmoset red blood cells (MaRBC). Because previous reports suggested the involvement of complement components in this phenomenon, the mechanism of rosette formation and the eventual similarities between the MaRBC receptor and the CR1 receptor present on human erythrocytes have been analyzed herein. The binding of MaRBC to human leukocytes strongly differs from the immune adherence phenomenon: rabbit anti-human CR1 did not react with MaRBC and the MaRBC receptor-binding activity is Ca2+-dependent. Rosette formation required intact energy metabolism and cytoskeleton integrity of leukocytes. Our attempts to purify the receptor from MaRBC membranes revealed the absence of CR1. Nevertheless, C3-binding proteins were isolated by selective desorption by Sepharose iC3 column chromatography. A three-band pattern was observed under reduced conditions with 74,000, 70,000, and 53,000 molecular weights. It was not possible to further separate these components. This protein complex inhibited the rosette phenomenon between MaRBC and both Raji and U-937 cells, exhibited a very poor cofactor activity, and had no decay-accelerating activity toward the classical C3 convertase. This material did not cross-react with antibodies directed to human proteins. These results showed that erythrocytes from new world monkeys do not express a receptor analogous to the human CR1, but expressed C3-binding protein with low cofactor activity that could recognize membrane-associated complement components.