Purification and physicochemical properties of C1q from guinea-pig serum

Anti-inflammatory drugs modulate C1q secretion in human peritoneal macrophages in vitro

The complement system plays an important role in the humoral immune response. Activation of the classical complement pathway is mediated by its subcomponent, C1q, which is involved in the pathogenesis of several autoimmune disorders. Among the main C1q-synthesising tissues, macrophages have been attributed as the main source. We investigated the effects of anti-inflammatory drugs (methylprednisolone and acetylsalicylic acid (ASA)) on C1q secretion in human peritoneal macrophages in vitro. The macrophages were isolated from peritoneal lavage fluid of patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis, and were maintained in culture for up to 6 days. ASA decreased while methylprednisolone increased C1q secretion from human peritoneal macrophages in vitro, which correlated well with the percentage of CD14 positive cells after treatment. We conclude that different response of the macrophages to treatment with methylprednisolone and ASA may point out to the importance of macrophage activation after treatment, as well as an increased abundance of membrane C1q accompanied by increased phagocytosis.

Rapid isolation and biochemical characterization of rat C1 and C1q

Using a human IgG-Sepharose column to which rabbit anti-human IgG was bound (rabbit anti-human/human IgG-Sepharose), human and rat C1 or C1q were isolated from serum in a single step, and the C1q further purified to homogeneity by FPLC. This procedure allowed the rapid isolation of haemolytically active C1 or C1q, with a yield equal to or greater than published methods. The availability of human and rat C1q allowed comparison of the two molecules, revealing differences in their mobility on SDS-PAGE as well as on agarose gel electrophoresis. Amino terminal sequence analysis demonstrated greater than 78% residue identity between rat C1q A, B and C chains and the published human and mouse sequences. Similar amino acid compositions suggest that the homology extends throughout the molecules. In addition to the major A:B and C:C dimer bands, rat, unlike human C1q, contained minor dimer species. These may reflect heterogeneity in glycosylation and or lysine and proline hydroxylation.

Biosynthesis of the subcomponents C1q, C1r and C1s of the first component of complement (C1) by guinea pig hepatocyte primary cultures

Thus far, the synthesis of C1q by liver cells has not been demonstrated. To investigate this possibility, viable hepatocytes were isolated from the liver of guinea pigs and primary cultures were established. The cells (10(6) cells/ml) were cultured under serum-free conditions for 8 days and the culture medium was changed every 24 h. The few contaminating Kupffer cells were lysed by preincubating the cell cultures with a monoclonal (22C4-8) antibody directed against a nonpolymorphic Ia determinant and preabsorbed rabbit serum. The hemolytic activity of C1 and its subcomponents C1q and C1r/C1s was tested in the supernatants. Guinea pig hepatocyte primary cultures synthesize and secrete up to 3 X 10(3) effective C1q molecules/cell/24 h and 34 X 10(3) effective C1r/C1s molecules/cell/24 h. The synthesis of C1q and C1r/C1s could be reversibly inhibited by cycloheximide (50 micrograms/ml). Furthermore, to demonstrate de novo synthesis of the C1q subcomponent, endogeneous labeling with 3H-proline (or 14C-proline) was performed. The immunoprecipitated C1q from cellular lysates and culture medium was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Compared to biosynthetically labeled guinea pig C1q from peritoneal macrophages, three corresponding bands (30, 28 and 24 kDa, respectively) were detectable in the fluorograph. The data show that guinea pig hepatocytes are able to synthesize C1 subcomponents, whereby the synthesis of C1q and C1r/C1s occurs independently.

Isolation and characterization of macrophage-derived C1q and its similarities to serum C1q

Recently, we have shown that the collagen-like, Fc-recognizing subcomponent C1q of the first complement component is synthesized by human, guinea pig and mouse peritoneal macrophages. To test whether macrophages may contribute to the serum pool of C1q, C1q was purified from guinea pig serum and from guinea pig peritoneal macrophage supernatants and compared for similarities. Both molecules had a similar sedimentation rate (macrophage C1q: 11.3 S, serum C1q: 11.2 S) and showed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions three identical bands with molecular weights of Mr, 29 000, Mr, 27 000 and Mr 23 000 for the A, B and C chains, respectively. Both C1q molecules migrated by immunoelectrophoresis in the gamma region and, in Ouchterlony analysis, showed complete antigenic identity with rabbit anti-serum C1q. These experiments demonstrate the antigenic and protein chemical similarities between serum C1q and C1q secreted by macrophages supporting the idea that macrophages have to be considered as one potential source of serum C1q. Furthermore, macrophage-derived C1q may be of importance in the local microenvironment at an inflammatory site involving macrophages.

Rat Clq: isolation and purification from normal serum and development of a sensitive hemolytic assay

Rat Clq was isolated and purified from normal rat serum by a two-step procedure: affinity chromatography on a human IgG-Sepharose 4B column and Bio-Gel A 5m column chromatography. From 1.8 l of normal serum, the procedure yielded 4.5 mg of homogeneous and hemolytically active rat Clq as shown by three bands of peptide in SDS polyacrylamide gel electrophoresis under reducing conditions and by a single precipitin line between rat Clq and rabbit anti-rat Clq antibody. Rabbit anti-rat Clq antibody prepared by immunizing a rabbit with 225 micrograms of rat Clq was specific as shown by a single precipitin line between the antibody and normal rat serum and rat Clq with complete identity. The amino acid composition of rat Clq was very similar to that of human Clq. The purification procedure also yielded Clq-depleted rat serum which was used with the homogeneous Clq to establish a sensitive hemolytic assay: 4.5-13.5 ng of rat Clq can be reproducibly quantitated. The concentration of Clq in Brown Norway rats was estimated to be 41.5 +/- 3.0 micrograms/ml serum.

Isolation of pig Clq and its structural and functional characterization

Pig Clq, a subcomponent of the first component of complement, was isolated in a fully hemolytically active form using precipitation in the presence of chelating agents at low ionic strength. Three times precipitated Clq was highly purified as shown by immunoelectrophoresis, polyacrylamide gel electrophoresis and ultracentrifugation. The yield of Clq using this method ranged from 40 to 55%. Pig Clq was also purified using precipitation with EDTA followed by affinity chromatography on a pig IgG-Sepharose 4B column. However, overall recovery of Clq was only about 10%. The purified Clq was heat-labile (56 degrees C, 30 min) both structurally and functionally, had an apparent molecular weight of 400 600 daltons as determined by ultracentrifugation, and restored the hemolytic complement activity of Clq-depleted sera of various species thus confirming interchangeability of this subcomponent. Cross-reactivity of pig, human, guinea-pig, mouse, rat and frog Clq-containing sera with monospecific anti-pig Clq antiserum showed a high degree of antigenic similarity.

Development of a novel C1q immunoadsorbent for removal of circulating immunecomplexes: quantitative isolation of hepatitis B virus surface antigen and immunecomplexes

A technique for large scale production of human C1q from plasma by affinity chromatography on an anti-C1q column is described. Affinity purified C1q was covalently coupled to a newly developed agarose polyacrolein microsphere beads immunoadsorbent. This immunoadsorbent was utilized for quantitative removal of artificially formed bovine serum albumin (BSA)-anti-BSA immune complexes (IC). The C1q affinity column was then used for the isolation of immunecomplexes containing hepatitis B virus (HBV) surface antigen (HBsAg) from serum of an HBsAg carrier. Identical columns may be utilized for quantitative removal of a variety of IC from blood of patients with infectious and autoimmune diseases, as well as neoplastic diseases. Furthermore, dissociated immunecomplexes will provide an additional source for purification of specific antigens.

Purification and characterization of human, guinea pig and mouse C1q by fast protein liquid chromatography (FPLC)

A simple and rapid procedure for the purification of C1q from human, guinea pig and mouse serum is described. This procedure allows the purification of C1q within one and a half days using euglobulin precipitation, chromatography on Superose 6B, followed by chromatography on Mono S by Fast Protein Liquid Chromatography (FPLC). The highly purified, hemolytically active C1q is free of any immunoglobulins. Since the purification of C1q of three different species was performed by the same purification procedure, a comparison of the subunit compositions was made under reducing and non-reducing conditions on SDS-PAGE. The yield was found to be more than 50%.

Protein A treatment of cancer: activation of a serum component with trans-species anti-B16 melanoma activity

Mice (C57BL) succumbed to cultured B16 melanoma cells i.p. with reproducible kinetics and an MST2 of about 26 days. Serum from tumour-bearing or normal mice was treated at 0 degree C with fixed SAC cells and injected i.p. into fresh tumour-bearing mice. If serum was given 7 days or less after B16 inoculation, the MST of the mice was highly significantly increased by up to 32%. Similar activity has been generated in normal human, rabbit and guinea-pig serum, while untreated sera were ineffective. Apparently the sera contained an inactive native precursor that was activated by the SAC to produce an anti-tumour agent. Precursor and product were both relatively labile at 0 degree C. Anti-tumour activity was eluted at pH 2.5 from SAC or Sepharose-protein-A pretreated with serum, thus implicating the protein A component of SAC. The eluates contained haemolytically active C1, the first component of complement, and five crude C1 preparations made by standard methods showed good anti-tumour activity. However, seven other highly haemolytic C1 preparations had no anti-tumour effect. Similarly, two crude preparations of the subcomponent C1q had good anti-tumour activity, but eight other, more pure and highly haemolytic C1q preparations were inactive in mice. Thus the anti-tumour principle was not C1 or C1q alone, although it had some chemical properties in common with these substances. It remains unidentified, but has potential interest for cancer therapy.

Synthesis of complement by macrophages and modulation of their functions through complement activation

During the last decade considerable progress has been made to characterize intimate functional links between macrophages, a major cellular component of immunoinflammatory responses, and the complement system representing the major humoral mediator of inflammation. Macrophages of various species and tissue sites have been shown to synthesize and release most of the complement components providing these cells with their own "pericellular" complement system. Circumstantial evidence for the assembly of both classical and alternative pathway convertases has been adduced. An intricate network of feedback loops involving endogenous and extrinsic factors operates to adjust complement production to acute requirements, for example augmenting production in the face of accelerated turnover at sites of inflammation, and returning it to baseline levels once the inflammatory stimulus has subsided, in order to maintain a fine-tuned balance. The molecular mechanisms underlying regulation of complement synthesis by macrophages are beginning to be elucidated by use of gene technology. On the other hand, complement activation products exert a number of effects on macrophages via specific surface receptors causing internalization of offending agents, microbes, and immune complexes, promotion of intracellular killing, controlling migration behavior, inducing release of potent biologic substances such as lysosomal enzymes, arachidonic acid metabolites, and interleukin 1. In these interactions, two important humoral mediator systems of inflammation, the complement system and the arachidonic acid cascade, are functionally linked at the level of the macrophage. Stimulation of the release of immunomodulating compounds from macrophages invoke a role for complement in immune regulation. This multifaceted interplay is of particular importance considering the mobility of macrophages that allows them to gain almost unrestricted access to sites of ongoing immunoinflammatory responses. The time seems to have come to abandon the petrified thinking in socalled systems as, for instance, humoral versus cellular, specific versus unspecific, and to proceed to interlocking functions guided by physiology proper.