- Research Article
- Open Access
Reduced Immune Complex Binding Capacity and Increased Complement Susceptibility of Red Cells from Children with Severe Malaria-Associated Anemia
© Feinstein Institute for Medical Research 2008
- Received: 3 September 2007
- Accepted: 21 November 2007
- Published: 1 March 2008
Plasmodium falciparum malaria causes 1–2 million deaths per year. Most deaths occur as a result of complications such as severe anemia and cerebral malaria (CM) (coma). Red cells of children with severe malaria-associated anemia (SMA) have acquired deficiencies in the complement regulatory proteins complement receptor 1 (CR1, CD35) and decay accelerating factor (DAF, CD55). We investigated whether these deficiencies affect the ability of erythrocytes to bind immune complexes (ICs) and regulate complement activation. We recruited 75 children with SMA (Hb ≤ 6 g/dL) from the holoendemic malaria region of the Lake Victoria basin, western Kenya, and 74 age- and gender-matched uncomplicated malaria controls. In addition, we recruited 32 children with CM and 52 age- and gender-matched controls. Deficiencies in red cell CR1 and CD55 in children with SMA were accompanied by a marked decline in IC binding capacity and increased C3b deposition in vivo and ex vivo. Importantly, these changes were specific because they were not seen in red cells of children with CM or their controls. These data suggest that the declines in red cell CR1 and CD55 seen in children with SMA are of physiologic significance and may predispose erythrocytes to complement-mediated damage and phagocytosis in vivo.
Plasmodium falciparum is an intracellular parasite of humans that is transmitted by the bite of Anopheles mosquitoes. It is responsible for 1–2 million deaths per year, the majority of which occur in sub-Saharan Africa (1). The invasion and growth of the parasite in erythrocytes is a prominent part of the life cycle and is associated with most of the morbidity and mortality. Severe anemia is one of the major complications of infection with P. falciparum malaria (2). The pathogenesis of this anemia is not understood well. Although destruction of erythrocytes takes place by the direct effect of the parasite, the degree of anemia in severe cases cannot be explained solely on this basis(3–5). Therefore, uninfected erythrocytes must be affected and destroyed as well. Several studies have documented that the life span of uninfected erythrocytes is decreased in persons infected with P. falciparum and in animal models (3,4). Earlier studies by Facer et al. (6,7) reported the presence of C3d on the surface of erythrocytes from children with malaria. These observations motivated us to determine whether there is a defect in the complement regulatory protein machinery of red cells in children with severe malaria associated anemia (SMA).
Red cell complement regulatory proteins protect the cells from autologous complement attack. Complement receptor 1 (CR1, CD35), decay accelerating factor (DAF, CD55), and the membrane inhibitor of reactive lysis (MIRL, CD59) are erythrocyte surface proteins that promote the inactivation and binding of C3b in immune complexes (ICs) (CR1), promote inactivation of C3b convertases (CR1 and CD55), and interfere with the assembly of the membrane attack complex C5b-9 (CD59)(8,9). Red cells are able to bind C3b-bearing ICs via CR1 and carry them to the liver and spleen where they are removed from circulation (10,11). Consequently, complement regulatory proteins may play an important role in protecting red cells from complement-mediated destruction as a result of IC formation and complement activation that occur during malaria infection (12–15).
We have shown that red cells of children with SMA have decreased levels of CR1 and CD55 (14,16,17). We hypothesized that these changes could translate into a decreased functional capacity to bind ICs and prevent complement deposition, which could result in their increased rate of destruction. To test our hypothesis we carried out a case-control study in children with SMA and age and gender-matched symptomatic uncomplicated malaria controls and determined their levels of erythrocyte CR1 and CD55, their erythrocyte IC binding capacity, and the susceptibility of their red cells to complement deposition in vivo and ex vivo. As an additional comparison group, we recruited children with cerebral malaria (CM) and age- and gender-matched symptomatic uncomplicated malaria controls.
Study Design and Populations
Participants were recruited under a human use protocol approved by the Human Use Research Committee, the Walter Reed Army Institute of Research, and the National Ethics Review Committee of the Kenya Medical Research Institute. Informed consent was obtained from all parents or guardians. The study had a matched case-control design. SMA cases, defined as children with asexual P. falciparum parasitemia by Giemsa-stained thick and thin blood smear and Hb ≤ 6 g/dL, were recruited from the pediatric ward of the Nyanza Provincial General Hospital (NPGH), Kisumu, Kenya, where malaria is holoendemic. Because CM is uncommon in this area, CM cases were recruited from the pediatric ward of the Kisii District Hospital (KDH), as well as from the NPGH. KDH is located in the highlands of western Kenya where transmission is seasonal and, consequently, it receives many more CM cases than the NPGH(18). CM was defined as asexual P. falciparum parasitemia by Giemsa-stained blood smear and a Blantyre coma score of < 2(19), lasting at least 30 min if there was a history of convulsions. Symptomatic uncomplicated malaria controls matched by gender and age ± two months were assigned to each case at a case:control ratio of 1:1 for SMA and 1:2 for CM, and were identified from the outpatient clinic of the same hospital where the corresponding case was recruited. Controls were defined as children with a normal mental status, a Hb > 6 g/dL, a Giemsa-stained blood smear positive for asexual P. falciparum, and an axillary temperature ≥ 37.5°C. In the absence of fever, we required two of the following signs or symptoms: nausea/vomiting, irritability, poor feeding, myalgias, or headache. General exclusion criteria also included evidence of concomitant serious infections (i.e. meningitis excluded by lumbar puncture when indicated, pneumonia, sepsis), chronic illness, or a history of blood transfusion in the three months preceding enrollment to avoid the influence of donor erythrocytes in our measurements.
All children were evaluated in a standardized fashion at enrollment and at follow-up two months later. If a child failed to return for follow-up, a field worker traveled to his/her last known domicile to determine his/her status. During follow-up, a blood sample was obtained once it was confirmed that the child was asymptomatic and free of parasitemia. If malaria persisted at the first follow-up visit, the child was re-treated and re-evaluated two weeks later. Inpatient treatment for malaria consisted of IV quinine (2) and outpatient therapy was with artemether/lumefantrine (20).
To compare the results to a normal population we also present data on a set of 79 normal individuals 12 to 45 years of age who were recruited in a recent cross-sectional study (manuscript in preparation).
Blood Samples and Smears
Giemsa-stained thick and thin blood smears, and thin reticulocyte smears stained with new methylene blue (Sigma-Aldrich, St. Louis, MO, USA), were prepared from capillary blood obtained by finger prick. A 2.5 mL sample of venous blood was obtained at enrollment and 5 mL at follow-up. Hemoglobin levels were measured from EDTA-anticoagulated blood using a hematology analyzer (Coulter, Hialeah, FL, USA). The EDTA-anticoagulated blood was centrifuged and the plasma was stored at −70°C for use as part of other ongoing studies. The erythrocyte pellet was washed once with 50 volumes of Alsevers buffer and a portion resuspended in the same volume of buffer for storage at 4°C until used. The remaining pellet was washed with ten volumes of phosphate buffered saline pH 7.4 (PBS) and resuspended in glycerolyte (50% glycerol, 16 g/L sodium lactate, 300 mg/L KCl, 25 mM sodium phosphate pH 6.8) for cryopreservation in liquid nitrogen (21).
Flow Cytometric Measurement of CR1 and CD55
Preparation of ICs, IC Opsonization, and IC Binding Capacity
Fifty µL of 49 mg/mL rabbit anti-BSA (Accurate Chemical and Scientific Corp., Westbury, NY, USA) and 3 µL of 5 mg/mL BSA-FITC (Sigma-Aldrich) were added to 950 µL of RPMI 1640 (Sigma-Aldrich). This combination was noted to be the point of equivalence in preliminary experiments. The mixture was incubated at 37°C for 1 h and overnight at 4°C. The next day, the precipitate was centrifuged at 10,000g for 10 min. The pellet was washed twice with RPMI and resuspended in 500 µL of RPMI. The IC preparation was made fresh weekly, aliquoted, and stored at −20°C.
For IC opsonization, 5 µL of stock IC was incubated in a total volume of 100 µL containing 30% AB + serum ± 20 mM EDTA (negative control) at 37µC for 30 min with constant rocking motion. In the meantime, 100 µL of Alsevers buffer containing thawed or freshly collected erythrocytes from study participants or from an aparasitemic standard control was added to individual wells of a separate 96-well plate. After centrifugation at 500g for 5 min, the cells were resuspended in 100 µL of plain RPMI1640. This was followed by the addition to separate wells of IC opsonized with or without EDTA, or of plain RPMI 1640 (unstained control). To determine to what extent the opsonized ICs were binding to red cell CR1, some red cell samples were pre-incubated with RPMI 1640 containing a 1:20 dilution of chicken anti-CR1 Fab (Accurate) or an irrelevant chicken Fab prepared from whole IgY (Accurate) using a Fab preparation kit (Pierce Biotechnology Inc., Rockport, IL, USA) followed by the addition of IC and incubation as above. Following the incubation with IC, the erythrocytes were washed twice in 200 µL of ice cold RPMI1640, resuspended in PBS containing 1% paraformaldehyde, and stored at 4°C until acquisition. After gating, the erythrocyte FITC fluorescence was measured using logarithmic amplification and the cut off for the positive red cells was set using the unstained cells. The percent of positive red cells (IC binding capacity) was calculated based on this cut off. To control for day-to-day variation, the IC binding capacity was normalized to the mean IC binding capacity of the red cell standard used throughout using a formula similar to the one used for correction of the CR1 and CD55 MFI (above).
Measurement of Complement Susceptibility
All centrifugation steps were at 500g for 5 min. Rabbit polyclonal anti-C3a (negative control antibody) and anti-C3b (Accurate) were pre-adsorbed ×3 by adding a 1:50 dilution of antibody in PBS to an equal volume of packed pre-washed erythrocytes from the normal standard control. The cells were incubated for 1 h at 37°C with constant rocking followed by centrifugation. The pre-adsorbed antibody was frozen at −20°C in single-use aliquots. 100 µL pre-washed fresh or thawed erythrocytes in Alsevers buffer was added to wells of a 96-well plate and resuspended in PBS (baseline C3b determination) or PBS containing 30% AB + serum ± 20 mM EDTA plus IC to induce complement activation. The IC was used at a dilution that induced a predetermined amount of C3b deposition on standard cells, which in most cases was 1:20. After incubation for 10 min at 37°C, the cells were washed twice in PBS and resuspended in 50 µL of pre-adsorbed rabbit anti-C3b, anti-C3a, or in PBS (unstained control), and incubated for 10 min at 37°C. After two washes, the cells were resuspended in 1:50 anti-rabbit PE (Sigma-Aldrich) for 30 min at room temperature, washed twice, resuspended in PBS. Acquisition was carried out as above. Red cells with IC deposition (FITC-positive) were excluded from the analysis gate. The baseline C3b MFI was adjusted by subtracting the C3a MFI. To subtract the baseline C3b contribution after complement activation with IC, C3b MFI obtained in samples incubated with EDTA was subtracted from the C3b MFI in samples without EDTA.
Statistical analysis was carried out using SPSS v11.5 (Spss Inc., Chicago, IL, USA). To compare the clinical parameters at enrollment or follow-up between cases and controls or between SMA and CM cases, we used the paired or independent samples t-test respectively. For the complement regulatory protein levels, IC binding capacity, and C3b MFI, the primary comparisons were between cases at enrollment and follow-up, and between cases and controls at enrollment. For this, we used the general linear model (GLM) to carry out matched one-way analysis of variance (ANOVA) across the three levels (cases at enrollment and follow-up, and controls at enrollment) including a term when appropriate for sample type (fresh or frozen). Dunnett’s test was used to adjust for multiple comparisons using the cases at enrollment as the comparator. To compare controls at enrollment and follow-up, we used the paired t-test. Categorical variables were compared using the Pearson chi-square. All tests were two-sided with α ≤ 0.05.
Demographics and Clinical Characteristics of the Participants
Clinical and demographic characteristics of the study groups
Nyanza Provincial General Hospital (NPGH)
Kisii District Hospital (KDH)
Cases (N = 75)
Controls (N = 74)
Cases (N = 8)
Controls (N = 15)
Cases (N = 24)
Controls (N = 37)
Mean age (SD) in months
No. Females (%)
Mean Haemoglobin (SD) g/dL
%Corrected Reticulocyte (SD)d
Mean # Parasites/µL × 10−3 (SD)
Home District (%)
Ethnic group (%)
Levels of Red Cell Complement Regulatory Proteins CR1 and CD55
IC Binding Capacity
We measured complement deposition on red cells at baseline and after in vitro complement activation via the classical pathway using ICs. We present these results as the C3b MFI of the total red cell populations in the gate after exclusion of FITC-positive (IC-bearing) cells. Both fresh and frozen samples were used in these assays and therefore, we controlled for this variable in the final models.
Upon activation of the complement cascade via the classical pathway, C3b deposition was measured as MFI correcting for the baseline C3b deposition. The enrollment red cell C3b MFI was higher for children with SMA than for their controls (Figure 5B). The red cell C3b MFI for children with SMA dropped at follow-up but remained unchanged for their controls. On the other hand, the C3b MFI of red cells from children with CM did not differ from that of their uncomplicated malaria controls and did not change significantly between enrollment and follow-up (Figure 5D). The red cell C3b-MFI after complement activation was higher for children with SMA than for children with CM at enrollment (P = 0.02, 95% CI for the mean difference = 1.0 to 12.1).
Severe malaria-associated anemia is a complex phenomenon. Multiple pathophysiologic mechanisms have been proposed (23,24). In most cases, as in our series, the erythropoiesis is depressed as evidenced by an inappropriately low reticulocyte count. However, because of the 120-day lifespan of red cells, bone marrow depression alone cannot account for this manifestation. Central to the pathophysiology of this severe anemia is the destruction of uninfected erythrocytes (5). The mechanism of destruction remains unclear. Complement activation is a major suspect because complement deposition has been observed in red cells of children with malaria (6,7) and it is implicated in the removal of senescent and damaged erythrocytes from circulation (25). Therefore, we have concentrated on studying the complement regulatory protein machinery of red cells.
We reported previously that red cells of children with SMA have low levels of CR1 and CD55 and, in addition, have increased surface IgG and increased susceptibility to phagocytosis (16). Because CR1 and CD55 protect red cells from complement (C3b) attack, their reduced levels on red cells could result in increased C3b deposition at sites other than CR1 and CD55. We also have shown that these children have increased levels of circulating ICs (14,15). Thus, children with SMA have a source of complement activation and a defect that may sensitize erythrocytes to complement-mediated damage. In the present study, we set out to determine whether the deficiencies in erythrocyte complement regulatory proteins are physiologically relevant. We expanded the definition of severe anemia to include children with Hb ≤ 6 g/dL in an effort to detect children earlier in the path to severe anemia and to enhance our ability to detect early changes on erythrocytes prior to their removal from circulation. In addition, unlike previous studies of complement deposition on red cells of children with SMA (26), we included children with CM and their controls to determine the specificity of our findings.
The declines in the levels of erythrocyte CR1 and CD55 in children with SMA reported here are similar to the ones we have reported in previous studies(16,17). This decline is very specific to SMA because it is not seen in children with CM. Although the CR1 levels of CM controls at enrollment are significantly lower than at follow-up, there was no difference between CM cases and controls at enrollment (Figure 2). The high level of statistical significance for the comparison between CM controls at enrollment and follow-up is likely a reflection of the large number of controls. We have proposed that the loss of complement regulatory proteins is related to the repeated episodes of malaria attacks that are characteristic of areas of high intensity malaria transmission where severe anemia is most common, such as the Lake Victoria region of western Kenya (27). With each bout of malaria, ICs are formed and bound to CR1 on red cells. In the liver and spleen, the ICs are removed by macrophages together with membrane CR1 and possibly CD55(11,28–30).
Corresponding to the level of CR1, erythrocytes of children with SMA at enrollment have the lowest IC binding capacity of any group at any time. Although the absolute decline in IC binding capacity is small (95% CI for difference between SMA cases and controls at enrollment = 4.9%–9.5%), these changes represent declines of 25% to 38% of the median binding capacity. Thus, red cells of children with SMA have a significant decline in their ability to bind ICs. When not bound to red cells, the ICs can deposit in tissues and on the endothelium where they continue to activate complement and stimulate pro-inflammatory cytokines (30,31).
To assess the susceptibility of red cells to C3b deposition, we measured surface C3b both at baseline and after in vitro complement activation with IC. Because our detection antibody was raised against C3b, we cannot exclude the possibility that it recognizes terminal C3 components such as C3bi, and C3d,g also. However, C3b, C3bi, and C3d all can induce phagocytosis, especially in the presence of IgG (32–34), which we have shown to be present on red cells of children with SMA (16). Red cells of children with SMA had higher C3b deposition than their controls and CM cases, both at baseline and after complement activation as measured by C3b MFI. On the other hand, we saw no difference in the C3b deposition on red cells of children with CM and their controls.
Our data suggest that the deficiencies in complement regulatory proteins seen in the red cells of children with SMA translate in declines in the IC binding capacity and increases in complement susceptibility both in vivo and ex vivo. These changes, together with increased IgG deposition on red cells (16) and up-regulation of Fc and complement receptors on macrophages activated by TNF-α (23,35), are likely responsible for increased destruction of red cells in children with SMA. Further, the striking difference in findings between red cells of children with SMA and CM, despite similar parasite density, lend more strength to the hypothesis that the losses in CR1 and CD55 are significant contributors to, if not directly responsible for, the increased destruction of erythrocytes of children with SMA.
The views of the authors do not purport to reflect the position of the Department of the Army or the Department of Defense. The U.S. Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.
We would like to thank the children who participated in our studies, as well as their parents, for their willingness to contribute to this research endeavor. We are indebted to our dedicated staff of clinicians, nurses, drivers, and field workers who made these studies possible. We also thank Craig Morrissette for helpful comments on the statistical analysis. This work is published with the permission of the Office of the Director, the Kenya Medical Research Institute.
This work was supported in part by the US Army Medical Research and Materiel Command and by a grant from the National Heart Lung and Blood Institute (R01 HL 7502). Walter Otieno was supported by a training grant from the Fogarty International Center (1 D43 TW06239).
- World Health Organization. The World Health Report: Changing History. 2004. Geneva, WHO.Google Scholar
- World Health Organization CDC. (2000) Severe falciparum malaria. Trans. R. Soc. Trop. Med. Hyg. 94 Suppl 1:S1–90.View ArticleGoogle Scholar
- Coleman RM, Rencricca NJ, Rittershaus CW, Brissette WH. (1976) Malaria: decreased survival of transfused normal erythrocytes in infected rats. J. Parasitol. 62:138–40.View ArticleGoogle Scholar
- Salmon MG, de Souza JB, Butcher GA, Playfair JH. (1997) Premature removal of uninfected erythrocytes during malarial infection of normal and immunodeficient mice. Clin. Exp. Immunol. 108:471–6.View ArticleGoogle Scholar
- Jakeman GN, Saul A, Hogarth WL, Collins WE. (1999) Anaemia of acute malaria infections in non-immune patients primarily results from destruction of uninfected erythrocytes. Parasitology. 119(Pt 2):127–33.View ArticleGoogle Scholar
- Facer CA, Bray RS, Brown J. (1979) Direct Coombs antiglobulin reactions in Gambian children with Plasmodium falciparum malaria. I. Incidence and class specificity. Clin. Exp. Immunol. 35:119–27.PubMedPubMed CentralGoogle Scholar
- Facer CA. (1980) Direct Coombs antiglobulin reactions in Gambian children with Plasmodium falciparum malaria. II. Specificity of erythrocyte-bound IgG. Clin. Exp. Immunol. 39:279–88.PubMedPubMed CentralGoogle Scholar
- Parker CJ. (1992) Regulation of complement by membrane proteins: an overview. Curr. Top. Microbiol. Immunol. 178:1–6.PubMedGoogle Scholar
- Miwa T, Song WC. (2001) Membrane complement regulatory proteins: insight from animal studies and relevance to human diseases. Int. Immunopharmacol. 1:445–59.View ArticleGoogle Scholar
- Madi N, Paccaud JP, Steiger G, Schifferli JA. (1991) Immune complex binding efficiency of erythrocyte complement receptor 1 (CR1). Clin. Exp. Immunol. 84:9–15.View ArticleGoogle Scholar
- Reinagel ML, Gezen M, Ferguson PJ, Kuhn S, Martin EN, Taylor RP. (1997) The primate erythrocyte complement receptor (CR1) as a privileged site: binding of immunoglobulin G to erythrocyte CR1 does not target erythrocytes for phagocytosis. Blood. 89:1068–77.PubMedGoogle Scholar
- Jhaveri KN et al. (1997) Autoantibodies, immunoglobulins, complement and circulating immune complexes in acute malaria. Natl. Med. J. India. 10:5–7.PubMedGoogle Scholar
- Tyagi P, Biswas S. (1999) Naturally occurring plasmodia-specific circulating immune complexes in individuals of malaria endemic areas in India. Indian J. Malariol. 36:12–8.PubMedGoogle Scholar
- Stoute JA, Odindo AO, Owuor BO, Mibei EK, Opollo MO, Waitumbi JN. (2003) Loss of red blood cell-complement regulatory proteins and increased levels of circulating immune complexes are associated with severe malarial anemia. J. Infect. Dis. 187:522–5.View ArticleGoogle Scholar
- Mibei EK, Orago AS, Stoute JA. (2005) Immune complex levels in children with severe Plasmodium falciparum malaria. Am. J. Trop. Med. Hyg. 72:593–9.View ArticleGoogle Scholar
- Waitumbi JN, Opollo MO, Muga RO, Misore AO, Stoute JA. (2000) Red cell surface changes and erythrophagocytosis in children with severe Plasmodium falciparum anemia. Blood. 95:1481–6.PubMedGoogle Scholar
- Waitumbi JN, Donvito B, Kisserli A, Cohen JH, Stoute JA. (2004) Age-related changes in red blood cell complement regulatory proteins and susceptibility to severe malaria. J. Infect. Dis. 190:1183–91.View ArticleGoogle Scholar
- Hay SI, Noor AM, Simba M, Busolo M, Guyatt HL, Ochola SA, Snow RW. (2002) Clinical epidemiology of malaria in the highlands of western Kenya. Emerg. Infect. Dis. 8:543–8.View ArticleGoogle Scholar
- Molyneux ME, Taylor TE, Wirima JJ, Borgstein A. (1989) Clinical features and prognostic indicators in paediatric cerebral malaria: a study of 131 comatose Malawian children. Q. J. Med. 71:441–59.PubMedGoogle Scholar
- Kokwaro G, Mwai L, Nzila A. (2007) Artemether/lumefantrine in the treatment of uncomplicated falciparum malaria. Expert. Opin. Pharmacother. 8:75–94.View ArticleGoogle Scholar
- Cockburn IA, Donvito B, Cohen JH, Rowe JA. (2002) A simple method for accurate quantification of complement receptor 1 on erythrocytes preserved by fixing or freezing. J. Immunol. Methods. 271:59–64.View ArticleGoogle Scholar
- Snow RW et al. (1994) Severe childhood malaria in two areas of markedly different falciparum transmission in east Africa. Acta Trop. 57:289–300.View ArticleGoogle Scholar
- Akanmori BD et al. (2000) Distinct patterns of cytokine regulation in discrete clinical forms of Plasmodium falciparum malaria. Eur. Cytokine Netw. 11:113–8.PubMedGoogle Scholar
- Kurtzhals JA, Rodrigues O, Addae M, Commey JO, Nkrumah FK, Hviid L. (1997) Reversible suppression of bone marrow response to erythropoietin in Plasmodium falciparum malaria. Br. J. Haematol. 97:169–74.View ArticleGoogle Scholar
- Shapiro S, Kohn D, Miller B, Gershon H. (1994) Erythrocytes from young but not elderly donors can bind and degrade immune complex- and antibody-bound C3 in vitro. Clin. Exp. Immunol. 95:181–90.View ArticleGoogle Scholar
- Goka BQ et al. (2001) Complement binding to erythrocytes is associated with macrophage activation and reduced hemoglobin in Plasmodium falciparum malaria. Trans. R. Soc. Trop. Med. Hyg. 95:545–9.View ArticleGoogle Scholar
- Stoute JA. (2005) Complement-regulatory proteins in severe malaria: too little or too much of a good thing? Trends Parasitol 21:218–23.View ArticleGoogle Scholar
- Cornacoff JB, Hebert LA, Smead WL, VanAman ME, Birmingham DJ, Waxman FJ. (1983) Primate erythrocyte-immune complex-clearing mechanism. J. Clin. Invest. 71:236–47.View ArticleGoogle Scholar
- Cosio FG, Shen XP, Birmingham DJ, Van Aman M, Hebert LA. (1990) Evaluation of the mechanisms responsible for the reduction in erythrocyte complement receptors when immune complexes form in vivo in primates. J. Immunol. 145:4198–206.PubMedGoogle Scholar
- Waxman FJ et al. (1984) Complement depletion accelerates the clearance of immune complexes from the circulation of primates. J. Clin. Invest. 74:1329–40.View ArticleGoogle Scholar
- Wu X, Wittwer AJ, Carr LS, Crippes BA, DeLarco JE, Lefkowith JB. (1994) Cytokine-induced neutrophil chemoattractant mediates neutrophil influx in immune complex glomerulonephritis in rat. J. Clin. Invest. 94:337–44.View ArticleGoogle Scholar
- Ehlenberger AG, Nussenzweig V. (1977) The role of membrane receptors for C3b and C3d in phagocytosis. J. Exp. Med. 145:357–71.View ArticleGoogle Scholar
- Gaither TA, Vargas I, Inada S, Frank MM. (1987) The complement fragment C3d facilitates phagocytosis by monocytes. Immunology. 62:405–11.PubMedPubMed CentralGoogle Scholar
- Fishelson Z. (1991) Complement C3: a molecular mosaic of binding sites. Mol. Immunol. 28:545–52.View ArticleGoogle Scholar
- Kitagawa S et al. (1996) Activation of human monocyte functions by tumor necrosis factor: rapid priming for enhanced release of superoxide and erythrophagocytosis, but no direct triggering of superoxide release. Exp. Hematol. 24:559–67.PubMedGoogle Scholar