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PubMed1986

Mice naturally tolerant to C5 have T cells that suppress the response to this antigen.

We examined whether C5-sufficient mice which are naturally tolerant to this antigen have suppressor T cells to C5 humoral immune response. Two congenic strains of mice B10.D2 (NSN) and B10.D2 (OSN) differing only in the presence or absence of C5 were used. Irradiated (760 rds) sufficient hosts were reconstituted with a nonadherent spleen cell suspension from either sufficient or deficient mice or a mixture of both. Hemolytic C5 levels were assayed. Sufficient spleen cells appeared to prevent the drop of C5 level caused by anti-C5 antibody made by deficient spleen cells. Spleen cell suspensions from sufficient mice primed with deficient spleen cells exhibited better anti-C5 activity than normal sufficient spleen cell suspensions. This anti-C5 activity is abrogated by treatment of the NSN spleen cell suspensions obtained from NSN primed with OSN spleen cells with anti-Thy-1.2 antiserum and complement. Suppression of the humoral response to C5 failed to affect the anti-sheep red blood cell immune response. Suppressor T cells are resistant to low-dose irradiation, cortisone treatment and adult thymectomy. In contrast, they are sensitive to high doses of irradiation and both high and low doses of cyclophosphamide treatment. Thus, C5-sufficient mice, in contrast to C5-deficient mice, appear to have antigen-specific suppressor T cells which downregulate the humoral immune response to C5. In addition, we examined the relationship of these suppressor T cells to the state of tolerance in helper T cells of C5-sufficient mice. This was done in irradiated deficient mice which were repopulated with spleen cell suspensions selectively depleted of either Lyt-1+ or Lyt-2+ T cell subsets. These chimeras were challenged with murine C5 and both the primary and secondary immune response was measured by inhibition of the C5 hemolytic activity. It was found that only spleen cell suspensions of the deficient mice selectively depleted from the Lyt-2+ subset of T cells responded to the antigen both in the primary and secondary response. In contrast, either subset of T cells from the sufficient mice failed to respond. Thus, it appears that in sufficient mice helper T cells to C5 are intrinsically tolerant or physically and/or functionally deleted. In conclusion, the data suggest that both T cell compartments are unresponsive and play a role in the mechanism of tolerance to a physiologic antigen.

Animals↗

PubMed1999

Isolation and characterization of the eighth component of the bovine complement system.

OBJECTIVE: To isolate and characterize the eighth component of the complement system (C8) in cattle. SAMPLE POPULATION: Fresh plasma obtained from beef cattle. PROCEDURES: Plasma samples were fractionated, using sequential precipitation and ion-exchange and gel-filtration chromatography, to yield C8. The protein was identified throughout the procedure on the basis of its hemolytic function. Electrophoresis in polyacrylamide gels was used to determine molecular weight and composition of polypeptide chains. Reconstitution of classical and alternative complement pathways was used to characterize the hemolytic function of bovine C8. RESULTS: The bovine C8 protein consisted of a disulfide-bonded alpha-gamma heterodimer that was noncovalently associated with a beta chain. Apparent molecular weight of the alpha, beta, and gamma chains under reducing conditions were 66, 61, and 23 kd, respectively. In the classical pathway of activation, bovine C8 and the ninth component of the complement system (C9) had species incompatibility with human C8 and C9 on sheep erythrocyte target cells. CONCLUSIONS: A simple 4-step fractionation procedure provided good yield of bovine C8 from plasma. The isolated protein was structurally comparable to C8 from other species. Purified bovine C8 may be useful in functional hemolytic assays to investigate the roles of complement-mediated lysis in the pathogenesis of inflammatory diseases and the killing of susceptible microorganisms.

Animals↗

PubMedDate not supplied

Longitudinal study of the presence of hidden 19S IgM rheumatoid factor in juvenile rheumatoid arthritis.

Complement-fixing hidden 19S IgM rheumatoid factor (RF), i.e., 19S IgM RF that can be detected in the IgM-containing fraction by the hemolytic assay after separation of the serum by acid gel filtration, was evaluated serially (3 or more evaluations) over a 4-year period in 26 children with juvenile rheumatoid arthritis (JRA) correlating its presence with disease activity. Six children with continually active disease had consistently elevated hidden RF titers (26 evaluations), and the titers of 4 children with inactive disease remained insignificant (12 evaluations). Sixteen children had disease with variable activity over this period. Of these, 11 (43 evaluations) demonstrated positive correlation between disease activity and hidden RF titers. Five patients (8/20 evaluations) did not show correlation of disease activity with hidden RF titers. Thus, the presence of hidden RF correlated with disease activity in 93 of 101 evaluations. When hidden RF titers and the erythrocyte sedimentation rate were determined simultaneously on 40 occasions, the presence of hidden 19S IgM RF correlated significantly better (p less than 0.001) with disease activity.

Arthritis, Juvenile↗

PubMed1988

Human complement protein C9 is a calcium binding protein. Structural and functional implications.

Human complement protein C9 is shown to be a metalloprotein that binds 1 mol of Ca2+/mol of C9 with a dissociation constant of 3 micron as measured by equilibrium dialysis. Incubation with EDTA removes the bound calcium, resulting in a apoprotein with decreased thermal stability. This loss in stability leads to aggregation and, therefore, to loss of hemolytic activity upon heating to a few degrees above the physiological temperature. Heat-induced aggregation of apoC9 can be prevented by salts that stabilize proteins according to the Hofmeister series of lyotropic ions, suggesting that the ion in native C9 may ligand with more than one structural element or domain of the protein. Ligand blotting indicates that the calcium binding site is located in the amino-terminal half of the protein. Removal of calcium by inclusion of EDTA in assay mixtures has no effect on the hemolytic activity of C9, and its capacity to bind to C8 in solution, or to small unilamellar lipid vesicles at temperatures at or below the physiological range. Although we do not know yet the precise structural and functional role of the bound calcium, it is clear that it provides thermal stability to C9 and it may have a function in regulation of membrane insertion.

Calcium↗

PubMed1987

Biosynthesis of the third component of complement by the human monocyte-like cell line, U-937.

The human monocyte-like cell line, U-937, was shown to synthesize and secrete C3 by hemolytic assays, radioimmunoassays and metabolic labeling experiments. The daily synthesis of antigenic C3 by unstimulated U-937 cells was low (about 3 ng/10(6) cells/24 hr) over a 3 day period. Induction of the cells to differentiate into macrophage-like cells with phorbol myristate acetate (PMA), resulted in 5-fold augmentation of C3 synthesis and secretion into the culture medium. Using a plaque assay for enumerating C3 production by single cells, approx. 5% of unstimulated U-937 cells were found to secrete hemolytically active C3. The proportion of C3-plaque forming cells was increased about 6-fold in PMA stimulated cells. The synthesis of C3 by U-937 cells was reversibly inhibited by cycloheximide. Data from SDS-PAGE analyses showed that U-937 cells synthesized C3 as a precursor polypeptide chain and was capable of processing this pro-molecule into the secreted two chain form. C3 antigen immunoprecipitated from stimulated U-937 cell lysates showed an increased amount of low mol. wt material as compared to C3 antigen immunoprecipitated from the lysates of unstimulated cells. This may be attributable to increased intracellular proteolytic activity in the PMA stimulated cells. The studies show that the U-937 cell line provides a useful model for studies on the synthesis and processing of complement proteins and the physiological regulation of complement production.

Cell Line↗

PubMed1982

Release of soluble immune complexes from immune adherence receptors on human erythrocytes is mediated by C3b inactivator independently of Beta 1H and is accompanied by generation of C3c.

Antigen.antibody complexes (Ag.Ab) prepared from (125)I-labeled bovine serum albumin and guinea pig anti-albumin were incubated at 37 degrees C for 30 min with normal human serum diluted optimally for binding (1:16) and then with autologous erythrocytes (RBC). After washing, RBC-bearing antigen.antibody.complement complexes (Ag.Ab.C) were resuspended in serum reagents or solutions of purified complement components, and the kinetics of dissociation were analyzed. Ag.Ab.C dissociated in serum heated at 56 degrees C for 30 min (SDelta30) but not in serum heated for 120 min (SDelta120). Dissociation in SDelta30 markedly decreased after adsorption with anti-C3b inactivator but not anti-beta1H or anti-C4 binding protein (C4bp), and dissociation in SDelta120 markedly increased after addition of C3b inactivator. Hemolytic assays revealed that SDelta30 retained inactivator activity whereas SDelta120 lacked significant activity. Ag.Ab.C dissociated in the presence of purified inactivator or C3b but not beta1H or C3. Dissociation was more rapid with inactivator than with C3b and occurred at 0 degrees C as well as at 37 degrees C. Treatment with inactivator inhibitor abolished dissociation in SDelta30; dissociation in inactivator deficient serum was markedly reduced. Addition of beta1H did not enhance inactivator-mediated dissociation at limiting dilutions of inactivator, and adsorption of Ag.Ab.C with anti-beta1H or preparation of Ag.Ab.C with serum adsorbed with anti-beta1H did not diminish dissociation. After dissociation with inactivator, Ag.Ab.C were unchanged in size but were no longer able to bind to fresh RBC and gave enhanced binding to Raji and Daudi lymphoblastoid cells. NaDodSO(4)/polyacrylamide gel electrophoresis of Ag.Ab.C prepared with (125)I-labeled C3 revealed that, after binding to RBC, dissociation with inactivator was accompanied by generation of a C3 fragment the size of C3c. Preincubation of Ag.Ab.C with excess inactivator did not prevent subsequent binding of Ag.Ab.C to RBC but, immediately after binding, Ag.Ab.C dissociated rapidly. These findings indicate that C3b inactivator can release immune complexes from immune adherence receptors on human RBC, that release occurs independently of beta1H, alters cell binding properties of immune complexes, and involves multiple cleavages of the C3b alpha' chain, and that receptors in human RBC membrane are required for this C3b inactivator-mediated breakdown.

Antigen-Antibody Complex↗

PubMed1992

Soluble complement receptor type 1 ameliorates the local and remote organ injury after intestinal ischemia-reperfusion in the rat.

We examined the role of C activation in ischemia reperfusion injury by inhibiting C activation in a rat model of mesenteric arterial occlusion. In anesthetized rats, 60 min of mesenteric arterial occlusion was followed by 3 h of reperfusion. PBS alone or containing soluble C receptor 1 (3 or 6 mg) was administered i.v. Controls underwent laparotomy without ischemia. Relative serum C activities were assessed by hemolytic assay, neutrophil (polymorphonuclear leukocyte) sequestration by tissue content of myeloperoxidase (MPO) activity, intestinal mucosal injury by histologic grading, lung vascular permeability by the ratio of bronchoalveolar lavage to blood concentration of radiolabeled BSA, and endothelial cell injury was quantified by measurement of plasma factor VIII-related Ag. After reperfusion, PBS-treated animals had increased intestinal MPO (0.048 +/- 0.007 U/g) compared to sham (0.022 +/- 0.005 U/g (p less than 0.05)) and intestinal mucosal injury score (2.490 +/- 0.221) compared to sham (0.331 +/- 0.045 (p less than 0.05)). Treatment with 6 mg soluble C receptor 1 15 min before reperfusion reduced intestinal MPO (0.017 +/- 0.003 U/g (p less than 0.05)) and mucosal injury (1.733 +/- 0.168 (p less than 0.05)) compared to PBS control. PBS-treated animals also demonstrated increased lung MPO (0.314 +/- 0.025 U/g vs 0.085 +/- 0.018 in sham (p less than 0.05)) and increased lung permeability (bronchoalveolar lavage/blood cpm 11.32 +/- 1.35 x 10(-3) vs sham 2.22 +/- 0.19 x 10(-3) (p less than 0.05)). Treatment with 6 mg soluble C receptor 1 15 min before reperfusion or at reperfusion reduced the lung permeability (bronchoalveolar lavage/blood cpm 3.90 +/- 0.79 x 10(-3) and 5.08 +/- 0.75, respectively (both p less than 0.05)) compared to PBS control, but did not reduce lung MPO (0.342 +/- 0.031 U/g and 0.246 +/- 0.025), respectively. Treatment with sCR1 also reduced the release of factor VIII-related Ag, 5-day mortality, and C hemolytic activity. In this model, C is a major mediator of intestinal injury and extraintestinal injury.

Animals↗

PubMed1994

Residue at position 331 in the IgG1 and IgG4 CH2 domains contributes to their differential ability to bind and activate complement.

A conserved proline residue is found at position 331 in the CH2 domains of human IgG subclasses which fix complement. This residue is replaced by a serine in IgG4 which is inactive. To determine the role of residue 331 in the differential ability of human IgGs to activate the complement cascade, a pair of genetically engineered anti-dinitrophenol IgG1 and IgG4 antibodies with reciprocal mutations at position 331 were tested for their hemolytic activity as well as for their ability to bind C1q, activate C1 and cleave C4. The IgG1 Ser331 mutant was virtually unable to mediate the lysis of trinitrobenzene-sulfonic acid-derivatized sheep red blood cells as a result of a marked defect in C1q binding activity. In contrast, the substitution of Pro for Ser331 in IgG4 bestowed partial hemolytic activity (40%) to the IgG4 Pro331 variant. Under low ionic strength conditions, this mutant was found to be approximately 50 and 75% as active as wild-type IgG1 in the C1q binding and C4b deposition assays, respectively. These results indicate that residue Pro331, which folds into close proximity to a previously identified C1q binding motif (Duncan, A. R., and Winter, G. (1988) Nature 332, 738-740), contributes to the architecture of the IgG1 C1q binding site and that its replacement by a serine residue in IgG4 is largely responsible for the functional inactivity of this isotype.

Amino Acid Sequence↗

PubMed1991

Simple quantitative haemolytic microassay for determination of complement alternative pathway activation (AP50).

We describe here a simple, reliable and quantitative method to measure the alternative pathway (AP) dependent mode of complement activation for the lysis of rabbit erythrocytes. In the test the reciprocal of the plasma volume needed to destroy 50% of available rabbit erythrocytes is defined as the functional measure of this activity (AP50). The test was found to be highly reproducible both within and between assays with a coefficient of variation which was less than 5%. Sensitivity was also shown to be satisfactory and all of the plasma samples from the healthy blood donors which were tested could be assayed with precision. The specificity of the AP50 assay for AP complement activation was verified by the fact that a C4 affinity-depleted plasma gave an AP50 value within the normal range (52.8 U/ml) while a similar aliquot of the same plasma, affinity-depleted of factor B, gave an undetectable AP50 value (less than 10 U/ml). Furthermore, a sample was unable to lyse the target cells when heated to 50 degrees C or 56 degrees C, treatments which are known to destroy factor B and total haemolytic complement, respectively. To ensure inhibition of the classical pathway of activation. EGTA and MgCl2 were added during the assay. An advantage of this assay is that it is possible, using microplates, multipipettes and a spectrophotometer coupled to a computer, to semi-automate the procedure.

Animals↗

PubMed1983

Interaction of the eighth component of guinea pig complement (C8) with the membrane-bound C5b-7 complex. The binding site of C8 to C5b-7 is formed on association of the alpha-gamma subunit with the beta-chain.

The eighth component (c8) of guinea pig complement consists of three polypeptide chains, the alpha-, beta-, and gamma-chains with M.W. of 60,000, 60,000, and 24,000, respectively. The alpha- and gamma-chains are bound by a disulfide bond(s) forming an alpha-gamma subunit, which is linked noncovalently to the beta-chain. The alpha-gamma subunit and the beta-chain were separated and purified from C8 by treatment with sodium dodecyl sulfate (SDS) and gel chromatography on Sephacryl S-300 in the presence of SDS. After removal of SDS, neither alpha-gamma nor beta showed the hemolytic activity of C8 when assayed independently, but showed significant activity in combination, indicating reconstitution of active C8. The recovery of hemolytic activity was 3.48%. When alpha-gamma and beta were incubated successively with EAC-7 with intervening reconstitution of active C8 on the cells was insignificant, irrespective of the order of the reactions. alpha-gamma and beta did not bind to EAC-7 when added separately, but after recombination 7% of alpha-gamma and 9% of beta bound to EAC-7 when EAC-7 was in excess. These results indicate that the binding site of guinea pig C8 to the membrane-bound C5b-7 complex does not exist on either alpha-gamma or beta only but stretches over both or is formed on one subunit after recombination of the subunits.

Animals↗

PubMed1977

Detection of functional complement components in gingival crevicular fluid from humans with periodontal diseases.

Crevicular fluid was collected from patients with periodontitis by a capillary tube procedure. Complement component activities were determined by functional assay systems, with human complement, and partially purified human first complement component (C1) as controls. The complement-fixing properties of the dental plaque of each patient were also examined C1 activity in the crevicular fluid of all patients was approximately 1/8 of whole serum C1 and diminished rapidly with time after collection. There was no significant relationship between C1 concentration and crevicular fluid flow rate. Hemolytic activity of whole complement was also invariable detected when sufficient amounts (8 micronl) of crevicular fluid could be obtained. Dental plaque was found to fix C1. A role for crevicular complement in inflammatory periodontal disease is suggested.

Complement C1↗

PubMed1985

Effect of estrual stage on complement activity in bovine follicular fluid.

Ovaries were excised from 112 cows during specific stages of the estrous cycle and from cows with follicular cysts. Follicular fluid was collected from the largest follicle at estrus (d 1), metestrus (d 2 to 4), early diestrus (d 5 to 8), mid diestrus (d 9 to 14), late diestrus (d 15 to 18), proestrus (d 19 to 21), and from follicular cysts. Complement was measured with a standard hemolytic assay. Complement in follicular fluid varied with stage of cycle and was two to five times higher at estrus than at diestrus. Complement in follicular fluid was 5 to 22-fold higher than in blood serum. Blood complement was not influenced by stage of cycle. Cystic follicular fluid had complement amounts similar to that of metestrus follicles. The relationships of complement to ovulation, sperm maturation, fertilization, and sperm removal from the tract are discussed.

Animals↗

PubMed1990

Nonreciprocal complementation of the hlyC and lktC genes of the Escherichia coli hemolysin and Pasteurella haemolytica leukotoxin determinants.

The genetic organization of the Pasteurella haemolytica leukotoxin operon (lktCABD) is similar to that of the Escherichia coli hemolysin (hlyCABD). Their gene products share a sequence similarity of 66, 62, 90.5, and 75.6%, respectively. We investigated the role of the C proteins (LktC and HlyC) by performing reciprocal transcomplementation analyses in an E. coli recombinant background. In the absence of the C genes, neither LktA nor HlyA had their respective cytotoxic activities. When hlyC was provided in trans to lktA, the toxin that was produced had the same activity and target cell specificity as the wild-type leukotoxin; it was leukotoxic for bovine lymphoid cells but not human lymphoblast cells when it was evaluated by a 51Cr-release assay. We also detected a weak hemolytic activity for the active form of LktA against sheep erythrocytes. In contrast, an E. coli strain containing lktC with hlyA produced a form of HlyA which was neither hemolytic nor cytotoxic. A monoclonal antibody (D12) against HlyA which recognized an epitope specific to the active form of HlyA did not cross-react in immunoblots with LktA that was activated by either LktC or HlyC. We conclude that the mechanism for activation of leukotoxin and hemolysin by their respective C proteins (LktC and HlyC) is mechanistically similar but that the exact structural requirements involved in the process are different.

Bacterial Proteins↗

PubMed1979

Complement activation following intravenous contrast material administration.

Untoward reactions to iodinated contrast material (ICM) continue to be a significant medical problem. Complement components were assayed in patients having reactions to evaluate the possibility of complement activation in these reactions. Reactor group samples were drawn from patients during the contrast reactions and then 2 weeks later to provide the equivalent of preinjection baseline samples, Control patient values were determined from blood samples drawn from patients before and 20 minutes after ICM injections without reaction. There were consistent falls in total hemolytic complement (CH50) as well as C3, C4, and C5 in both the control group and the reactor group. These falls in the complement reached statistical significance only for CH50 in the reactor group. The results indicate that complement activation occurs after ICM injection. This activation can occur independent of clinical reactions; however, falls in total hemolytic complement and low hemolytic complement titers prior to ICM infusion may be related to the presence of anaphylactoid symptoms.

Adolescent↗

PubMed1984

Mediation of the killing of rough, mucoid isolates of Pseudomonas aeruginosa from patients with cystic fibrosis by the alternative pathway of complement.

The mechanism of killing of 12 serum-sensitive strains of mucoid Pseudomonas aeruginosa isolated from patients with cystic fibrosis was investigated. A quantitative assay indicated that more than 90% of cells were killed in 50% normal human serum (NHS). All strains failed to grow in NHS concentrations of greater than 10%. Killing was unaffected by adsorption of NHS with the mucoid bacteria or chelation with MgCl2-ethyleneglycol bis(beta-aminoethyl ether)N,N1-tetraacetate (MgCl2-EGTA) but was abolished in serum heated to 50 C for 20 min. Incubation of NHS with mucoid P. aeruginosa reduced the hemolytic capability of MgCl2-EGTA-chelated NHS against rabbit red blood cells by 56%-99%. Killing of the serum-sensitive mucoid strains was also seen in hypogammaglobulinemic serum. These data suggest that killing of such strains by NHS can occur via antibody-independent activation of the alternative pathway of complement. The importance of this finding lies in the implication that complement levels in the lungs of patients with cystic fibrosis who are colonized by these organisms are inadequate to deal with this chronic, progressive infection.

Adult↗

PubMed1981

Screening for deficiencies in the classical and alternative pathways of complement by hemolysis in gel.

Two assays based on hemolysis in gel were assessed for screening complement (C) component deficiencies. In one assay sensitized sheep erythrocyte (EA) were incorporated in agarose gel containing Ca2+ and Mg2+, in the other guinea pig erythrocytes (GpE) were used in the presence of Mg2+and EGTA. With few exceptions, fresh samples from healthy individuals produced homogeneous areas of complete hemolysis in both assays. Clearly aberrant patterns were observed in approximately 4% of healthy blood donors. Sera from patients having complete deficiencies of Clq, C2 or C4 produced clear lysis of GpE only, whereas in sera lacking C3 or C8 lysis was grossly impaired in both assays. Properdin deficient serum produced very slight lysis of GpE but normal lysis of EA. Reconstitution of these C-deficient sera gave normal lysis. Together, the two assays supplement immunochemical C3 and C4 determinations for screening out C disorders.

Animals↗

PubMed1976

Purification of the sixth and seventh component of human complement without loss of hemolytic activity.

Procedures for the isolation of the human complement proteins C6 and C7 have been described. These procedures allow isolation of the two proteins without any loss of hemolytic activity. Apparent activity gains of 160% and 140% were observed for C6 and C7, respectively, when the activity of the isolated proteins was compared with their activity in serum. The recovery of C6 was 3.5 to 11% and that of C7 was 7 to 13% of the amount present in serum. C6 has a m.w.of 128,000 and an electrophoretic mobility at pH 8.6 of -2.6 times 10(-5) cm2 s-1 v-1. C7 has a m.w. of 121,000 and an identical electrophoretic mobility. With 3 times 10(7) assay cells, 63% hemolysis was achieved with 1 ng of C6 and 3.8 ng C7. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and after reduction with mercaptoethanol, C6 and C7 behaved as single polypeptide chain proteins.

Complement C6↗

PubMed1990

Combined complete C5 and partial C4 deficiency in humans: clinical consequences and complement-mediated functions in vitro.

A family is described with two siblings who suffered at different times from a single episode of meningococcal meningitis by Neisseria meningitidis groups B and C, respectively. In the two subjects, hemolytically active fifth component of complement (C5) was not detectable and antigenic C5 was less than 0.05% and less than 0.7% of normal, respectively. Repletion of sera by purified human C5 (70 micrograms/ml) restored total complement hemolytic activities. The asymptomatic first degree family members had C5 levels compatible with a heterozygous state of C5 deficiency. C4 allotyping revealed an inherited partial deficiency (Q0) of C4A and C4B in the family with a combined C4AQ0 and C4BQ0 heterozygous condition in one and C4BQ0 heterozygosity in the other C5 deficient (C5D) subject. To our knowledge, this is the first human kindred with recognized combined C5 and C4 deficiency. No other defect of the humoral and cellular immune system was found in this family, including specific immune response to tetravalent meningococcal vaccine. The effect of partial C4 deficiency on classical pathway function was assessed by inhibition of immune precipitation (IIP) of forming bovine serum albumin (BSA)/anti-BSA immune complexes. Sera from all family members showed normal IIP values, with exception of the subject with combined partial deficiency in C4A, C4B, and complete deficiency in C5. Despite undetectable functional C5 in the C5D sera, the titration of the alternative pathway indicated intact but deficient hemolytic activities when rabbit erythrocytes (EC) were used as indicator cells in the presence of Mg2+ and EGTA in an end-point or kinetic assay. Preincubation of the two sera at 0 degrees C for 60 min with rabbit ECs reduced alternative pathway hemolytic activity by 24 and 100%, respectively. When rabbit ECs were replaced by guinea pig ECs no alternative pathway function could be measured. The results indicate that the apparent functional activity of the alternative pathway in C5D sera strongly depends on a factor(s) present in such serum and/or on the detection system used. We conclude that the two C5D individuals of the family reported here may not have sufficient C5 activity to provide efficient protection against Neisserial infections in conditions where complement functions beyond C3 opsonic activity are required in vivo.

Adolescent↗