Chemistry and reaction mechanisms of complement

Combining SPR with atomic-force microscopy enables single-molecule insights into activation and suppression of the complement cascade

Activation and suppression of the complement system compete on every serum-exposed surface, host or foreign. Potentially harmful outcomes of this competition depend on surface molecules through mechanisms that remain incompletely understood. Combining surface plasmon resonance (SPR) with atomic force microscopy (AFM), here we studied two complement system proteins at the single-molecule level: C3b, the proteolytically activated form of C3, and factor H (FH), the surface-sensing C3b-binding complement regulator. We used SPR to monitor complement initiation occurring through a positive-feedback loop wherein surface-deposited C3b participates in convertases that cleave C3, thereby depositing more C3b. Over multiple cycles of flowing factor B, factor D, and C3 over the SPR chip, we amplified C3b from ∼20 to ∼220 molecules·μm⁻². AFM revealed C3b clusters of up to 20 molecules and solitary C3b molecules deposited up to 200 nm away from the clusters. A force of 0.17 ± 0.02 nanonewtons was needed to pull a single FH molecule, anchored to the AFM probe, from its complex with surface-attached C3b. The extent to which FH molecules stretched before detachment varied widely among complexes. Performing force-distance measurements with FH(D1119G), a variant lacking one of the C3b-binding sites and causing atypical hemolytic uremic syndrome, we found that it detached more uniformly and easily. In further SPR experiments, K_D values between FH and C3b on a custom-made chip surface were 5-fold tighter than on commercial chips and similar to those on erythrocytes. These results suggest that the chemistry at the surface on which FH acts drives conformational adjustments that are functionally critical.

New milestones ahead in complement-targeted therapy

The complement system is a powerful effector arm of innate immunity that typically confers protection from microbial intruders and accumulating debris. In many clinical situations, however, the defensive functions of complement can turn against host cells and induce or exacerbate immune, inflammatory, and degenerative conditions. Although the value of inhibiting complement in a therapeutic context has long been recognized, bringing complement-targeted drugs into clinical use has proved challenging. This important milestone was finally reached a decade ago, yet the clinical availability of complement inhibitors has remained limited. Still, the positive long-term experience with complement drugs and their proven effectiveness in various diseases has reinvigorated interest and confidence in this approach. Indeed, a broad variety of clinical candidates that act at almost any level of the complement activation cascade are currently in clinical development, with several of them being evaluated in phase 2 and phase 3 trials. With antibody-related drugs dominating the panel of clinical candidates, the emergence of novel small-molecule, peptide, protein, and oligonucleotide-based inhibitors offers new options for drug targeting and administration. Whereas all the currently approved and many of the proposed indications for complement-targeted inhibitors belong to the rare disease spectrum, these drugs are increasingly being evaluated for more prevalent conditions. Fortunately, the growing experience from preclinical and clinical use of therapeutic complement inhibitors has enabled a more evidence-based assessment of suitable targets and rewarding indications as well as related technical and safety considerations. This review highlights recent concepts and developments in complement-targeted drug discovery, provides an overview of current and emerging treatment options, and discusses the new milestones ahead on the way to the next generation of clinically available complement therapeutics.

FURTHER STUDIES ON THE gammaG-HEAVY CHAIN GENE COMPLEXES, WITH PARTICULAR REFERENCE TO THE GENETIC MARKERS Gm(g) AND Gm(n)

The recently described Gm (g) and Gm (n) genetic markers of the γG3- and γG2-subgroups of γ-globulin were characterized in detail primarily through studies of myeloma proteins, their polypeptide chains and fragments. Antisera derived from rabbits, non-human primates and rheumatoid arthritis patients gave identical results. This contrasted with the Gm (b) system where the rabbit antisera react with a different genetic determinant (b⁰) than the sera from rheumatoid arthritis patients (b). The Gm (g) and Gm (n) antigens were detected both by precipitin analysis and by hemagglutination inhibition. The Gm (g) antigen was not associated with any of the other genetic antigens of the γG3-proteins which all belonged in the Gm (b) class. The genes for the latter were always allelic to the gene coding for Gm (g), with that for Gm (b⁰) constantly present when that for Gm (g) was absent. The Gm (g) and Gm (n) markers were of particular value in tracing the various gene complexes made up of the closely linked subgroup genes. Further support was gained for the concept that the different gene complexes of various population groups arose primarily through crossing-over. The Gm^g and Gm^b genes for the γG3-subgroup were extremely closely linked to those for the γG1-subgroup. However the Gm (n) marker indicated that the γG2-subgroup genes were probably further separated on the chromosome. Additional evidence was obtained for the γG2-γG3-γG1-order of the subgroup cistrons. Among the wide range of gene complexes a new type (γG2,—,γ/G1) was described. This complex appeared to have a deletion of the γG3-cistron. Lower levels of γG3-globulin were found in the sera of the individuals with this gene in the heterozygous state. The possibility that this unusual complex arose through an unequal nonhomologous crossing-over is discussed.

Agglutinability of cattle red cells. 3. Conglutination

Addition of both complement and conglutinin was necessary to conglutinate the cattle red cells (CRC) when they were sensitized by different blood typing reagents. Although the degree of conglutinability of the CRC was influenced by the particular blood factor-reagent combination the average conglutinability (i.e. average titre scores) of CRC from different MZ pairs varied from 1.9 to 16.2. The titres of complement varied from zero to 1:32, while the titres of conglutinin ranged from 1:8 to 1:1024 in the different sera from MZ cattle twins. The variance due to differences in the titre scores between MZ pairs was 82.2% for conglutinin and 68.3% for complement. There was no evident association between the titres of conglutinin and complement.

Agglutinability of cattle red cells. 4. The effect of antiglobulin in comparison with treatment by pronase

The average titre scores varied from zero to 24.7 for the cattle red cells (CRC) from different MZ pairs. These CRC were sensitized with different blood-typing reagents and were titre-tested against the double dilution series of an anti-bovine gamma-globulin serum. A significant negative correlation (r = - 0.82; P less than 0.001) was found between the degree of agglutinability and the amount of neuraminic acid of the surface component of CRC cleaved by pronase. After pronase treatment of the CRC it could be demonstrated that (1) the activity of the V and E'3 blood factors became destroyed; (2) three new specific receptors became evolved; (3) the degree of 'direct' agglutinability due to the A2, O3, W, S2 and Z anti-sera did not parallel with the titre scores obtained in the anti-globulin tests.

TEM immunogold staining of C3 from plasma onto titanium oxides

Immunogold staining in conjunction with TEM was used to observe C3 adsorption from plasma in relation to the underlying titanium structure of thermal, anodic, and electropolished oxides. Heat treatments and oxide thickness were found to have no significant effect on the adsorption behavior of C3, while surface oxide type possibly has. Surface concentration of C3 was found to be time- and plasma concentration-dependent. Evidence is given for the possible involvement of C3 in protein exchange, i.e., the Vroman effect. Diluted plasma resulted in a random distribution of gold colloids, whereas clustering occurred with undiluted plasma. Although C3 concentrations present on grain boundaries followed the same trend as that found on the surface, C3 was found to have a higher grain boundary than bulk concentration for 0.1% plasma.

Phagocytosis of virulent Porphyromonas gingivalis by human polymorphonuclear leukocytes requires specific immunoglobulin G

No studies to date clearly define the interactions between Porphyromonas gingivalis and human peripheral blood polymorphonuclear leukocytes (PMN), nor has a protective role for antibody to P. gingivalis been defined. Using a fluorochrome phagocytosis microassay, we investigated PMN phagocytosis and killing of P. gingivalis as a function of P. gingivalis-specific antibody. Sera from a nonimmune rabbit and a healthy human subject were not opsonic for virulent P. gingivalis A7436, W83, and HG405; phagocytosis of these strains (but not 33277) required opsonization with hyperimmune antiserum (RaPg). Diluting RaPg with a constant complement source decreased proportionally the number of P. gingivalis A7436 cells phagocytosed per phagocytic PMN. Enriching for the immunoglobulin G fraction of RAPg A7436 enriched for opsonic activity toward A7436. An opsonic evaluation of 18 serum samples from adult periodontitis patients revealed that only 3 adult periodontitis sera of 17 with elevated immunoglobulin G to P. gingivalis A7436 were opsonic for A7436 and, moreover, that the serum sample with the highest enzyme-linked immunosorbent assay titer was most opsonic (patient 1). However, the opsonic activity of serum from patient 1 was qualitatively and not just quantitatively different from that of the nonopsonic human sera (but was less effective opsonin than RaPg). Strain variability was observed in resistance of P. gingivalis to phagocytosis, and opsonization was strain specific for some, but not all, strains tested. An evaluation of killing of A7436 revealed that serum killing and extracellular killing of P. gingivalis were less effective alone when compared with intracellular PMN killing alone.

The role of chemical mediators in the pathogenesis of inflammation with emphasis on the kinin system

In recent years, numerous agents have been recognized as inflammatory mediators. In this review, however, we discuss only those having direct relevance to human inflammatory diseases These mediators are clinically important due to their proinflammatory properties such as vasodilatation, increased vascular permeability, pain and chemotaxis. They may lead to the fifth cardinal sign, loss of function in inflammatory diseases. Agonists and non-specific antagonists are used as pharmacological tools to investigate the inflammatory role of PGs, LTs, PAF, IL-1, histamine, complement, SP, PMN-leukocytes, and kallikrein-kininogen-kinin systems. Unfortunately, no compound is known which concurrently abolishes all actions and interactions of inflammatory mediators. Therefore it would be highly useful to promote efforts in developing selective and competitive antagonists against proinflammatory actions of these chemical mediators. This may help to a better understanding of the pathogenesis of inflammatory reactions, and it may also be useful for the therapy of inflammatory diseases.

IgG subclasses in gingival crevicular fluid from active versus stable periodontal sites

Since IgG subclasses are common immunoglobulins associated with the periodontium and have different biological characteristics, these subclasses were measured in gingival crevicular fluid (GCF) from periodontally active (greater than or equal to 2 mm clinical attachment loss within three months of sample) versus clinically similar but stable or healthy sites. A sandwich enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies was performed to quantitate IgG subclass and albumin concentrations in serum and interproximal GCF samples from at least one each of the three disease categories from each of 20 periodontal maintenance patients. Although much variability existed among sites, mean IgG1 (p less than 0.05) and IgG4 (p less than 0.01) concentrations were higher in GCF from active periodontitis areas than stable sites, even though both had similar clinical characteristics. When IgG subclass concentrations were adjusted per mg albumin, both IgG1 and IgG4 levels in GCF from active sites were still significantly elevated over stable areas (p less than 0.05). Mean adjusted concentrations in GCF were generally greater than in serum, especially for IgG4 (active site GCF:serum = 24.2:1). GCF IgG4 concentrations may be useful as an indicator of the immunopathological changes which occur in active periodontitis.

Serum IgG4 anti-Fab antibodies in rheumatoid arthritis are constitutively expressed

IgG4 comprises a significant proportion of the total anti-Fab antibody (aFABA) response in many but not all patients with rheumatoid arthritis (RA). Analyses of the dynamics of IgG aFABA subclass expression in 11 RA patients for periods of up to 11 months demonstrated that IgG4 aFABA was restricted to 6 of the 11 RA patients' sera initially studied and comprised approximately 25% (or more) of the total IgG aFABA response. Quantities of IgG4 aFABA in subsequent, serially obtained serum samples from these patients remained stable throughout the study period, whereas the remaining RA patients whose initial sera possessed small quantities of serum IgG4 aFABA failed to generate any augmented IgG4 aFABA response during the study. Elevated expression of IgG4 aFABA did not appear to be a consequence of a generalized polyclonal gammopathy or a generalized increase in autoantibody expression, though patients with higher total IgG4 serum levels expressed significantly greater quantities of IgG4 aFABA. These results indicate that the differential expression of IgG4 aFABA among RA patients reflects constitutive production within a subset of RA patients in whom IgG4 appears to comprise a significant proportion of the total IgG aFABA response.

Inhibitory effects of a novel synthetic protease inhibitor, FUT-175, on the paw edema in rats and zymosan-induced complement activation in vitro

FUT-175 inhibited the zymosan-induced rat paw edema in a dose-dependent manner, while indomethacin exhibited no significant activities in this model. FUT-175 also inhibited the decrease in hemolytic complement (CH50) induced by zymosan in vitro, and indomethacin was inactive. These results suggest that FUT-175 has potent in vitro and in vivo inhibitory activity against the activation of the complement system induced by zymosan.

Anti-Fab antibodies in humans. Predominance of minor immunoglobulin G subclasses in rheumatoid arthritis

Isoelectric focusing analyses of sera from patients with rheumatoid arthritis (RA) demonstrate two populations of antibodies directed against the Fab portion of pooled human IgG. One population is composed of polyclonal alkaline anti-Fab antibodies (alpha FABA) and the other, acidic alpha FABA which are more clonally restricted. In this study we have identified the immunoglobulin classes and subclasses of these antibodies in RA sera. Enzyme-linked immunosorbent assays (ELISA) demonstrated alpha FABA in RA sera to be predominantly IgG. A large portion of IgG alpha FABA existed as immune complexes, inasmuch as dialysis of RA sera against 6 M urea before ELISA analysis was necessary for maximal detection of alpha FABA activity. Chromatofocusing of RA sera isolated alpha FABA of different charges and revealed the acidic clonally restricted alpha FABA to be IgG4 and IgG3, whereas the polyclonal alkaline group contained IgG1, IgG2, and IgG3. Overall, acidic IgG3 and IgG4 comprised 70% of IgG alpha FABA, and high levels of IgG4 were seen in most RA sera. When alpha FABA were elevated in normal sera, they were primarily of the IgG4 subclass, and also existed as immune complexes. Serum anti-Fab activity was removed by adsorption of sera with Fab fragments. Anti-Fab antibodies of both kappa and lambda light-chain types were present in RA sera, and F(ab')2 fragments of RA serum immunoglobulin were found to possess anti-Fab activity. These studies indicate that alpha FABA in RA sera are limited to the IgG class, and that most of these antibodies exist as immune complexes and display clonal and minor IgG subclass restriction.

Respiratory infections may reflect deficiencies in host defense mechanisms

Serious respiratory tract infections are rare in the healthy individual and most of the nuisance morbidity that occurs results from nasopharyngeal viral infections that many people get once or twice a year. The economic impact from these upper respiratory tract infections is appreciable, however, in terms of absenteeism from school or work, but unfortunately there is little that can be done to ward them off in a practical way. Pneumonia is an infrequent lifetime experience for most non-smoking adults and when it occurs, unusual circumstances may pertain--a particularly virulent microorganism is in circulation, or perhaps one has been exposed to a newly recognized germ, such as has occurred with Legionella species in the past 8 years or so. What protects us the great majority of the time is a very effective network of respiratory tract host defenses. These include many mechanical and anatomical barrier mechanisms concentrated in nose and throat; mucociliary clearance, coughing and mucosal immunoglobulins in the conducting airways and in the air-exchange region of the alveolar structures, phagocytes, opsonins, complement, surfactant and many other factors combine to clear infectious agents. The ability to mount an inflammatory response in the alveoli may represent the maximal and ultimate expression of local host defense. In some way these host defenses are combating constantly the influx of micro-organisms, usually inhaled or aspirated into the airways, that try to gain a foothold on the mucosal surface and colonize it. But many general changes in overall health such as debility, poor nutrition, metabolic derangements, bone marrow suppression and perhaps aging promote abnormal microbial colonization and undermine the body's defenses that try to cope with the situation. It is a dynamic struggle. The departure from normal respiratory health may not be obvious immediately to the patient or to the physician and repeated episodes of infection or persisting symptoms of cough, expectoration and sinus or ear infections may develop before serious assessment of the situation is taken and appropriate diagnosis gotten underway. Obvious explanations for respiratory infections may be apparent and, nowadays, side effects from antineoplastic chemotherapy or immunosuppressive therapy for a variety of diseases that create an immunocompromised host are common. In a few subjects, especially young adults who present with a cumulative history of frequent but mild infections in childhood and youth, a subtle deficiency in host defenses may exist and have been partially masked because of attentive pediatric medical care and prompt use of broad spectrum antibiotics.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of the complement-component-C3b-binding site and the cofactor activity for factor I in the 38kDa tryptic fragment of factor H

Trypsin treatment of human factor H (H160) [enzyme/substrate ratio 1:100 (w/w), 30 min, 37 degrees C] generated a 38 kDa (H38) and a 142 kDa (H142) fragment linked by disulphide bonds (H38/142). The fragments were purified by reduction with 2-mercapto-ethanol, gel filtration on a Sephadex G-200 column and affinity chromatography with monoclonal anti-(factor H) antibody coupled to Sepharose 4B. This monoclonal antibody bound to a site in the 38 kDa fragment. To localize the C3b binding site in factor H we used two enzyme-linked immunosorbent assays (e.l.i.s.a.). For the first test, e.l.i.s.a. plates were coated with C3b; H160, H38/142, H38 and H142 were added, and their binding was monitored by goat anti-(factor H) and peroxidase-labelled rabbit anti-goat antibodies. Only intact factor H bound to the C3b-coated plates. For the second test, e.l.i.s.a. plates were coated with comparable amounts of factor H or its fragments, and C3b was offered at several dilutions. In contrast with the results from the first assay, C3b bound to intact factor H, H38/142 and H38 but not to H142, thus characterizing H38 as the fragment carrying the C3b-binding site. To identify the fragment responsible for the cofactor activity of factor H (cleavage of fluid-phase C3b by factor I), 125I-C3b was incubated with either H38 or H142 and factor I. H142 had no cofactor activity, whereas H38 had the same cofactor function as intact H. To further investigate the relationship between the C3b-binding site and the site of factor H essential for its cofactor activity, we made use of monoclonal antibodies directed against the H38. Those antibodies inhibiting the binding of C3b to H160 also inhibited the cofactor function, whereas those without effect on the C3b binding also did not interfere with the cofactor activity. This suggests that the C3b-binding site and the site essential for the cofactor activity of factor H are both localized in the 38 kDa tryptic fragment of factor H in close proximity or are identical.

Autolytic fragmentation of complement components C3 and C4 and its relationship to covalent binding activity

The autolytic cleavage reaction of C3 and C4 and the covalent binding reaction of these proteins, are both aspects of the reactivity of an activated thiolester within these proteins. Autolytic cleavage occurs by internal nucleophilic attack on one face of the planar thiolester, while the covalent binding reaction of the activated proteins follows exposure of the opposite face of the thiolester to attack by external nucleophiles. Although the autolytic cleavage reaction does not occur under physiological conditions, the study of this phenomenon has provided valuable evidence in support of the mechanisms postulated for the physiological covalent binding reactions. The ease with which autolysis can be induced and observed in C3, C4, and alpha 2 M has provided a valuable method for detecting the active forms of these proteins in circumstances where other assays are impracticable, as, for example, in the examination of the uptake of active C3 by lymphocytes. Autolytic cleavage has also been used by Karp and colleagues to produce fragments used in characterizing genetic and biosynthetic variants of mouse C4 and the mouse protein Slp, which is structurally similar to C4. Gross structural comparisons made among C3, C4, and alpha 2 M on the basis of alignment of the autolytic cleavage sites and the protease-activation sites in these proteins were useful in predicting how the alpha-, beta-, and gamma-chains of C4, or the alpha- and beta-chains of C3, were aligned in the single polypeptide chain pro-forms of these proteins. The beta-alpha-gamma alignment deduced for C4 was also found by Goldberger and Colten. Similar alignments of cleavage sites have been used as a basis for evolutionary comparisons of complement proteins and alpha 2 M from species other than man. Although autolytic cleavage has been described only for C3, C4, alpha 2 M, and Slp, it is likely that other proteins will be found that exhibit this phenomenon. A possible candidate is pregnancy-associated plasma protein A (PAPP-A) which resembles alpha 2 M in many respects. The autolytic cleavage reaction will serve as a useful indicator in the detection of other proteins that undergo covalent binding by the mechanism discussed above.

C3b acceptors on macrophages: inhibition of Fc gamma-receptor-mediated phagocytosis by acceptor-bound C3b

The binding of nascent human C3b (i.e. the fragment of C3 just after trypsin cleavage) to mouse peritoneal macrophages was demonstrated by immune adherence. Acceptor-bound C3b could be detected longer than 24 h on the cell membrane. The rosette formation and phagocytosis of SRBC coated with anti-SRBC rat IgG was inhibited by preincubation of the cells with C3 and trypsin (15 min, 37 degrees C). However, the phagocytosis of opsonized yeast particles was not influenced by acceptor-bound C3b, proving that C3b-C3b acceptor interaction did not alter the function of C3b-receptors. Acceptor-bound C3b on the macrophages failed to mediate phagocytosis of human 0,Rh+ red cells having C3b-receptors.

Electron microscopy of the complement protein C1q from the bullfrog, Rana catesbeiana

The complement protein C1q, isolated from bullfrog (Rana catesbeiana) serum, was found by electron microscopy to resemble human C1q; peripheral globular units, probably six in number, are connected by thin strands to a hollow stem-like central structure. The dimensions of frog and human C1q were also found to be very similar. These results are consistent with earlier observations that frog and human C1q are similar, although not identical, in overall size, subunit structure, amino acid composition, and functional properties. Evidently this protein, which binds to antigen-antibody complexes and to C1r and C1s, thereby forming a physical link between the immune and complement systems, has been highly conserved in evolution.

Contrasuppression. A novel immunoregulatory activity

We have described an interaction between two T cells subsets that results in interference with the expression of Ly-1-, 2+ (Ly-2) T cell-mediated suppression. We refer to this novel immunoregulatory activity as contrasuppression. The T cell responsible for the induction of contrasuppression (inducer cell) expresses the phenotype Ly-1-, 2+;I-J+;Qa-1+. This phenotype distinguishes it from the suppressor effector cells which we find to be I-J-2.3. An I-J+ soluble mediator from the contrasuppressor inducer cell acts on another cell (acceptor cell) that expresses the phenotype Ly-1+, 2+; I-J+; Qa-1+. This phenotype distinguishes it from T helper cells. Both the inducer cell (or its biologically active mediator) and its acceptor cell are required for the expression of contrasuppression. Because contrasuppressor cells can block the suppressive activity of cell-free mediators released by Ly-2 suppressor T cells, the mechanism of contrasuppression is either separated from or in addition to the inactivation of suppressor cells themselves. The potential importance of contrasuppressor activity in the regulation of suppressor T cell activity in allowing immunologic memory to be expressed and in permitting microenvironmental immune regulation is discussed.

Studies on circulating soluble immune complexes of the liver disease. 6. Comparative studies of 125I-pRF inhibition assay, 125I-Clq inhibition assay and 125I-Clq binding assay

Inhibition assay of 125I-C1q binding to IgG-p-azobenzamidoethyl Sepharose 6B (IgG-Sepharose) by immune complexes was developed for the detection of circulating soluble immune complexes in the liver disease and was compared with polyclonal rheumatoid factor (pRF) binding inhibition assay and with C1q binding assay. The C1q inhibition assay was proved to be very sensitive, reproducible and rapid. Sucrose density gradient ultracentrifugal analysis showed that the assay could detect aggregates of human IgG (AHGG) larger than 19s. C1q inhibition activity (C1qIA) correlated with severity of the liver disease, defined by histological criteria. The highest C1qIA was observed in sera of patients with primary biliary cirrhosis, followed by liver cirrhosis, fulminant hepatitis, chronic aggressive hepatitis (2B), lupoid hepatitis and hepatocellular carcinoma in the order. There were correlations of C1qIA with serum gamma-globulin levels, sero-positivity for rheumatoid factor and hepatitis B surface antigen, and significant correlations existed also among pRFIA, C1qIA and C1qBA. Ultracentrifugal analysis of sera from patients with the liver disease showed that ClqIA demonstrated two sizes of immune complexes, 7s and larger than 19s, while complexes larger than 8s were seen in pRFIA.

Isolation and characterization of mouse C1q

C1q was isolated from mouse serum and ascites fluid by absorption onto human IgG-coated latex beads followed by separation on 3-10% exponential gradient sodium dodecyl sulfate (SDS) polyacrylamide gels. Mouse C1q was also purified by low ionic strength precipitation of mouse serum. The purified C1q was heat-labile (56 degrees C, 30 min) both structurally and functionally, contained 4.3% hydroxyproline, 1.38% hydroxylysine, and 18.5% glycine, had an apparent molecular weight of 380,000 daltons, and reconstituted the hemolytic complement activity of C1q-depleted mouse serum. The negatively stained ultrastructural appearance of this purified material consisted of 6 globular units connected by strands. These data demonstrate that mouse C1q structurally and functionally is similar to human and rabbit C1q. A portion of polyacrylamide gel containing mouse C1q was injected into rabbits resulting in the production of monospecific antisera against mouse C1q. Thus, this procedure is a new, rapid and simple method to obtain monospecific antisera against mouse C1q.

Biosynthesis of the complement components and the regulatory proteins of the alternative complement pathway by human peripheral blood monocytes

Short-term cultures of human peripheral blood monocytes were shown to synthesize the alternative pathway complement components C3, factors B (B) and D (D), and properdin, the regulatory proteins C3b inactivator (C3bINA) and beta 1H, in addition to C2, C4, and C5. B, D, properdin, C3bINA, and C2 were detected by functional assays, whereas beta 1H, C4, C3, and C5 could only be detected using immunochemical procedures. Immunoperoxidase localization studies showed that all the cells in each culture contained each component, so it is possible that all monocytes synthesize each component. It is concluded that cells of the monocyte-macrophage series form a mobile source of complement components and regulatory proteins which can be concentrated at sites of inflammation.

Particle counting immunoassay (PACIA). III. Automated determination of circulating immune complexes by inhibition of an agglutinating factor of mouse serum

A factor capable of agglutinating human IgG coated particles (latex) has been found in mouse serum. This factor (MAG) was used in an unpurified form to detect circulating immune complexes in the particle counting immunoassay (PACIA) system, which allows measurement of agglutination with great precision. MAG did not react with monomeric IgG, nor with reduced and alkylated aggregated IgG. It was inhibited by immune complexes in small antigen excess. Among the various subclasses of IgG, IgA and IgM, only IgG1 and IgM when coupled to Sepharose beads displayed an inhibitory activity towards MAG. That the inhibitory factors detected in serum were immune complexes or aggregated Ig was suggested by the correlation obtained with the amounts of 'heavy' IgG found in the serum samples by Ultrogel chromatography and by the polydisperse distribution of the inhibitory factors in the heavy fraction of gradient ultracentrifugation.

The significance of serial measurement of serum anti-native DNA antibodies and complement C3 and C4 components in the management of patients with systemic lupus erythematosus

Serial measurements were made over a period of three years of serum DNA-binding capacity and complement C3 and C4 levels in parallel with documentation of clinical features of disease activity in Glasgow patients with SLE. Raised DNA-binding levels were noted in 27 of the 32 patients over this time period. High levels (over 80%) were found in patients with both renal and non-renal disease. In some patients increases in DNA-binding capacity and decreases in C3 levels were associated with changes in disease activity. This pattern was commonest in patients with renal SLE. In others DNA-binding capacity was elevated without any relationship to SLE disease activity. A fall in serum C3 levels was usually significant while serum C4 levels frequently fell without any change in clinical features of disease activity. Very low serum C4 levels (below 15 mg/dl), however, were usually of clinical relevance. The uses of immunological measurements in the differential diagnosis of a major illness in a patient with SLE are discussed. The finding of such an illness in a patient with normal serum DNA-binding levels made it unlikely that the illness was due to an exacerbation of the SLE and more likely that an alternative cause such as supervening bacteraemia was responsible.

Disorders of leukocyte chemotaxis

The rapid accumulation of inflammatory cells at sites of microbial invasion or neoplastic transformation is a central event in immunologically-mediated host defense. The availability of methodology to accurately quantify leukocyte migration in vitro has allowed the disclosure of previously unrecognized clinical disorders, namely leukocyte dysmotility syndromes. Although this area of clinical investigation is in its infancy, one can identify several processes associated with abnormal leukocyte accumulation. Abnormalities of immune recognition, chemotactic factor production, cellular motility or inhibitors of chemotaxis have been identified in different human diseases. In the upcoming years, pharmacological intervention directed at correcting specific causes of leukocyte dysmotility may well enhance our ability to treat certain infectious, inflammatory, and neoplastic diseases.