Immunosuppressive therapy for kidney transplant prevents vaso-occlusive crisis in a haemoglobin SC disease patient

Although the molecular basis of sickle cell disease (SCD) is well established, the wide variability in clinical manifestations still puzzles haematologists and clinicians. Recently, SCD started to be considered by different groups as a chronic inflammatory condition, where the inflammatory tendency of each individual could drive more or less severe clinical features. Here we describe a haemoglobin SC disease patient (heterozygous to both HbS and HbC variants) that experienced several vaso-occlusive crises before underwent a successful kidney transplantation. Since then (16 years ago), she is on uninterruped immunosuppressive therapy, and do not experienced any severe vaso-occlusive crisis. Considering SCD associated morbidity as a result of exacerbated immune responses, we suggest that the immunosuppressive therapy directed to the kidney graft maintenance is actually also helping in the control of the chronic inflammatory responses associated to SCD.     

Immunological studies in sickle cell disease: comparison of homozygote mild and severe variants

Cellular and humoral immune functions in patients suffering from severe and mild forms of homozygous sickle cell disease (SCD) were compared with those of healthy control subjects. Random neutrophil migration, chemotactic activity, and lymphocyte transformation index were all defective in individuals with severe variants of SCD when compared with individuals with mild disease or healthy controls. In contrast, serum opsonization activity was significantly reduced in both severe and mild variants of SCD. There were no statistical differences between serum immunoglobulin (IgA, IgG, and IgM) or complement C3 levels in any of the three groups. These results demonstrate that even though individuals with the mild variant of SCD possess two S genes, their immune functions are generally normal and in parallel with their clinical and hematological status. The one area of impaired immune function is their defective serum opsonization activity and this may explain their sensitivity to certain infections.     

Severity in phenotypic expression of homozygous sickle cell disease (Hb.SS) – Does hypermelanotic or hypomelanotic skin status of affected patients play a role?

Abnormal hemoglobin distribution on global map, of which hemoglobin S (Hb.S) accounted for about 80% of the disorders resulting from them are more prevalent in the tropics and sub-tropics. Homozygous sickle cell disease (Hb.SS) is the most common and most severe form of sickle cell disease (SCD) in phenotypic expression. The prevalence and severity in phenotypic expression of SCD had been noted to decrease farther away from the equatorial region, with prevalence rate of sickle cell trait of about 2% and less than 1% in North African coast and South Africa, respectively, compared to about 10-40% in the equatorial region. Controlling for human migration, the distribution of prevalence and severity of SCD tend to correspond with the degree of pigmentation of skin color on global map with areas of hyperpigmentation having the likelihood of higher prevalence and severity, while areas of hypopigmentation are characterized by the reverse. This distribution had been observed to correspond with skin color variation on global map based on Von Luschan's chromatic scale. Empirical observation had also shown that individual homozygous SCD patients who are lighter in skin color tend to manifest a less severe phenotypic expression of the disease condition when compared to those with darker skin color using the yard stick of frequency in sickle cell crises. The hypothesis is; would hypermelanotic or hypomelanotic skin status of individual homozygous SCD patient, if measured objectively by assessing the types and quantity of melanin in individual patient, influence the severity in phenotypic expression of SCD in affected patients. Oculocutaneous albinism (OCA) which is characterized by hypomelanosis is an inherited autosomal recessive disorder like SCD. OCA is also common in the tropics and sub-tropics like SCD. It had been reported that OCA does occur co-morbidly with homozygous SCD. Comparing a group of patients with co-morbid OCA and homozygous SCD with another group with SCD, who do not have OCA on severity of phenotypic expression of SCD could provide a feasible means of testing the hypothesis. If future carefully controlled studies confirm the hypothesis of influence of hypermelanotic or hypomelanotic skin status of the individual patients on severity in phenotypic expression of homozygous SCD, genetic and pharmacological interventions aimed at regulation of melanin production may play a role in alleviating the severity in phenotypic expression of SCD in affected patients.     

Heterogeneity of sickle cell anaemia in Arabs: review of cases with various amounts of fetal haemoglobin.

A study is presented on eleven patients with homozygous sickle cell anaemia. They are non-Sheeah Arabs from the United Arab Emirates on the south-eastern coast of the Arabian Peninsula. The proportions of fetal haemoglobin in these patients are variable, and there is a marked variation in the severity of their disease condition; these facts are not related. African sickle cell gene admixture is a likely affecting factor.     

Sequential development of human herpes virus 8-positive diffuse large B-cell lymphoma and chronic myelomonocytic leukemia in a 59 year old female patient with hemoglobin SC disease

Hematolymphoid neoplasms, including lymphoma and myeloid neoplasms, can occur in patients with sickle cell disease (SCD) or equivalent hemoglobinopathy, but an underlying connection between the two conditions has yet to be fully determined. Herein, we report a unique case of sequential development of two separate hematolymphoid neoplasms, human herpes virus 8 (HHV8)-positive diffuse large B-cell lymphoma (DLBCL) and chronic myelomonocytic leukemia, in a 59 year-old African American female with hemoglobin SC disease. While etiology of immunodeficiency is unknown, the potential causes include hydroxyurea therapy, disease related immunomodulation, chronic inflammation, and relatively old age. The leukemia cells demonstrated profound trilineage dysplasia and harbored complex cytogenetic abnormalities with loss of chromosome 5q and 7q, which are often observed in therapy-related myeloid neoplasms. Besides the potential causes listed above, we propose that myeloid leukemia in this setting may result from genomic changes due to excessive hematopoietic replication triggered by a hemolysis-induced cytokine storm. While myeloid neoplasms in the setting of SCD seems to herald a dismal clinical outcome per the literature, the HHV8-positive DLBCL in our case was apparently indolent, opposing the current perception of its clinical outcome.     

Transfusion in Sickle cell disease: best practice and understanding of its utility

Transfusion therapy remains an important treatment modality for patients with sickle cell disease (SCD). Transfusions are given not only to treat symptomatic anaemia, but also to decrease SCD‐related complications by lowering the percentage of circulating sickle red cells, thus decreasing blood viscosity and vaso‐occlusion. The strongest evidence of the effectiveness of transfusion is in primary and secondary stroke prophylaxis, where transfusion reduces the risk of overt stroke by about 90–70%, and in pre‐operative transfusion, where transfusion reduces the risk of acute chest syndrome by at least 30%. Most other indications for transfusion in SCD are based on expert opinion or less well‐controlled studies. In this brief overview, we discuss methods of transfusion, the evidence and expert opinion regarding various indications in sickle cell disease and our current pathophysiologic understanding of how transfusions may work in SCD.     

Ethical Challenges in Hematopoietic Cell Transplantation for Sickle Cell Disease

Hematopoietic cell transplantation (HCT) using an HLA-identical sibling donor offers a very high likelihood of cure with good outcomes for patients with sickle cell disease (SCD), and alternative donor HCT for SCD is an area of active clinical research. Thus, HCT is a potential option for a growing number of patients with SCD. This expanded use of HCT has raised several ethical questions. Who is eligible for HCT, in terms of both disease severity and psychosocial factors? Should affected children with matched sibling donors undergo HCT only when they have declared themselves as having significant symptomatology? Regarding donors, special ethical challenges include the use of preimplantation genetic diagnosis to conceive an HLA-identical sibling. In this review, we critically analyze various ethical challenges related to HCT for SCD, and offer recommendations to guide clinical care.     

Type 2 cytokine serum levels in healthy sickle cell disease patients.

Sickle cell disease (SCD) is characterized by significant morbidity and early mortality. Children with this hemoglobinopathy exhibit many of the manifestations associated with immunodeficiency disorders. Serum was obtained from 56 healthy SCD subjects and 45 normal healthy controls. Type 2 cytokines interleukin (IL)-4, IL-6, and IL-10 serum levels were measured. Concentrations were determined by reference to a standard curve, and results were expressed in pg/mL. Results revealed significant levels of IL-4 in 6 (13%) of 45 SCD patients compared with 1 (2%) of 45 controls. Increased levels of IL-6 were present in 35 (78%) of 45 SCD patients and 12 (41%) of 29 controls. Elevated levels of IL-10 were detectable in 13 (41%) of 42 SCD patients and 1 (4%) of 25 controls. High circulating levels of type 2 cytokines may suppress both humoral and cell-mediated immune functions in SCD, with resultant increased morbidity.     

Neutrophils as drivers of vascular injury in sickle cell disease

While neutrophils are the main effectors of protective innate immune responses, they are also key players in inflammatory pathologies. Sickle cell disease (SCD) is a genetic blood disorder in which red blood cells (RBCs) are constantly destroyed in the circulation which generates a highly inflammatory environment that culminates in vascular occlusions. Vaso-occlusion is the hallmark of SCD and a predictor of disease severity. Neutrophils initiate and propagate SCD-related vaso-occlusion through adhesive interactions with the activated and dysfunctional endothelium, sickle RBCs, and platelets, leading to acute and chronic complications that progress to irreversible organ damage and ultimately death. The use of SCD humanized mouse models, in combination with in vivo imaging techniques, has emerged as a fundamental tool to understand the dynamics of neutrophils under complex inflammatory contexts and their contribution to vascular injury in SCD. In this review, we discuss the various mechanisms by which circulating neutrophils sense and respond to the wide range of stimuli present in the blood of SCD patients and mice. We argue that the central role of neutrophils in SCD can be rationalized to develop targets for the management of clinical complications in SCD patients.     

Severe vaso-occlusive episodes associated with use of systemic corticosteroids in patients with sickle cell disease

Patients with sickle cell disease (SCD) are occasionally prescribed systemic corticosteroids to treat steroid-responsive conditions. Additionally, use of systemic corticosteroids for sickle cell pain episodes and acute chest syndrome is under investigation. We report 4 patients with SCD who developed severe vaso-occlusive events following the administration of systemic steroids. We also review similar cases from the literature and suggest measures for reducing the potential risk associated with use of systemic corticosteroids in this group of patients. We conclude that corticosteroids should be used with caution in patients with SCD.     

Low cobalamin levels in African Americans with and without sickle cell disease

About 7% of the adult population has subclinical cobalamin (B12) deficiency. Subjects with sickle cell disease (SCD) may be at higher risk of cobalamin deficiency because of increased demand, inadequate supply, coexisting folate deficiency or malabsorption. We compared the clinical and laboratory characteristics of low serum cobalamin levels in patients with SCD with those patients without this hemoglobinopathy (non-SCD). Between 1993 and 2003, 105 SCD patients and 112 non-SCD patients who had serum cobalamin measurements were identified at our institution. The mean cobalamin level in SCD patients was significantly lower (496 +/- 352 pg/ml) than that in patients without SCD (869 +/- 660 pg/ml, p<0.0001). The frequency of low cobalamin levels, defined by a serum cobalamin level of <200 pg/ml, was 18.1% (19/105) and 9.8% (11/112) in SCD and non-SCD patients, respectively (chi2=3.11, nonsignificant). The mean age of the low-cobalamin SCD and non-SCD patients was 28.1 and 62.9, respectively, and their male:female ratios were 11:8 in SCD patients and 2:9 in non-SCD patients. None of the SCD patients had neurological manifestations, but nine of the 11 non-SCD low-cobalamin level patients did. The proportion of SCD patients with unexplained low cobalamin levels (13/19) was higher than that in non-SCD patients (4/11, chi2=2.92, nonsignificant) Our data suggest that cobalamin levels are lower in SCD patients than in subjects without SCD, and low-cobalamin SCD patients are younger and more likely to be males.     

Polymorphisms of chemokine receptors and eNOS in Brazilian patients with sickle cell disease

Sickle cell disease (SCD) is an inherited disorder that presents extremely variable clinical manifestations. For the past few decades, it has been approached as an inflammatory disorder, and several researchers have tried to determine the factors involved in such characteristic. In order to contribute to the identification of the genetic differences underlying this phenotypic diversity in SCD, we proposed to study the distribution of polymorphic variants of the genes encoding the chemokine receptors CCR2 and CCR5, as well as three polymorphisms in the NOS3 gene, in Brazilian SCD patients. These genes are involved in the development of inflammatory immune reactions, a feature believed to be of extreme importance in SCD pathology. Our results indicate that the polymorphisms studied here are not directly associated with severe clinical manifestations in SCD patients. Nevertheless, we observed a tendency for the development of a severe clinical course in carriers of the variant alleles CCR2-64I and CCR5delta32 and in homozygotes for the -786C variant of the NOS3 gene. Further studies should be carried out in order to assess the role of such variants in the clinical picture of SCD.     

Pattern of Serum Cytokine Expression and T-Cell Subsets in Sickle Cell Disease Patients in Vaso-Occlusive Crisis

The pathogenesis of sickle vaso-occlusive crisis (VOC) in sickle cell disease (SCD) patients involves the accumulation of rigid sickle cells and the stimulation of an ongoing inflammatory response, as well as the stress of infections. The immune response, via cytokine imbalances and deregulated T-cell subsets, also has been proposed to contribute to the development of VOC. In this study, a panel of high-sensitivity cytokine kits was used to investigate cytokines in the sera of SCD patients in VOC. The results were compared primarily with those for stable SCD patients and secondarily with those for normal healthy people who served as controls. The cytokines studied included interleukin-2 (IL-2), IL-4, and IL-10. Lymphocyte subsets of patients with VOC were also studied and were compared with those of both control groups (20 stable patients without crisis [SCD group] and 20 normal healthy controls [NHC]). The VOC group was notable for remarkably elevated levels of IL-4, among the three cytokines tested, compared with those for the SCD and NHC groups. Patients with VOC also differed from stable SCD patients and NHC by having notably lower IL-10 levels, as well as the lowest ratio of CD4⁺ to CD8⁺ T cells (0.7). The patterns of the proinflammatory cytokine IL-2 did not differ between VOC and stable SCD patients, but NHC had significantly lower IL-2 levels than both the VOC and SCD groups. Our results demonstrate coexisting levels, both high and low, of TH1- and TH2-type cytokines, as well as diminished levels of T-cell subsets in VOC. These results are discussed in an effort to better understand the importance of the immune system profile in the pathogenesis of sickle cell VOC. Since the possibility that a cytokine imbalance is implicated in the pathogenesis of sickle cell crisis has been raised, our results should prompt further investigation of the host immune response in terms of TH1 and TH2 balance in sickle cell crisis.Sickle cell disease (SCD) is a chronic, incurable condition presenting primarily as anemia (sickle cell anemia [SCA]) in people homozygous for hemoglobin S (HbS). This abnormal hemoglobin, resulting from the replacement of glutamic acid at position 6 of the β-globin chain by valine, is responsible for erythrocyte distortion and fragility in these patients, as well as for thrombosis, fever, splenomegaly, joint pain, lethargy, and weakness. Sickle cell crises refer to the sudden attacks of pain, at various levels of severity, that occur during the lifetime of the patient with sickle cell disease (1, 3). Of these, the painful vaso-occlusive crisis (VOC) is the most common and is characterized by fever, leukocytosis, joint effusions, and tenderness, which occur in about 50% of patients at initial presentation (2), as well as by susceptibility to infection. It is a medical emergency and an acute crisis state. Patients in a state of well-being between these episodes are referred to as “steady-state” SCD patients.The sequence of pathophysiological events that lead to the sickle cell VOC is not well understood. Several authors (8, 13, 27, 28) have outlined a sequence of steps occurring in the microcirculation that culminate in this painful sickle cell crisis. Polymerization of HbS, decreased blood red cell flexibility, microvascular occlusion, hypoxia of tissue involved with the occluded microvascular network, and tissue damage triggering painful stimuli have been mentioned (26), although the precise dynamics of these events and their interrelationships are poorly understood. Tissue ischemia due to vascular occlusion causing infarctive tissue damage, which in turn initiates secondary inflammatory responses, has also been mentioned (3, 4). Ischemic events produced by the occlusion of both large and small blood vessels are stressful and involve intricate interactions between red blood cells, the endothelium, and leukocytes (7). These interactions are known to be regulated by cytokines secreted by T cells as well as by adhesion molecules, and consequently, the immune response is implicated in the initiation and development of the sickle cell crisis. Indeed, studies now show that immune subsets are operative in sickle cell disease (9, 14, 16, 25), and the susceptibility of sickle cell disease patients in crisis to infections that specifically require the help of T cells to be cleared, such as Salmonella enterica serovar Typhimurium osteomyelitis (14), is suggestive.CD4⁺ T cells, subdivided based on their associated cytokines, play a crucial role in inflammatory responses and the elimination of infection. TH1 cells provide immunity against intracellular pathogens by secreting the cytokines interleukin-2 (IL-2), IL-12, and gamma interferon (IFN-γ), whereas commitment to the TH2 lineage programs the clearance of extracellular pathogens and the secretion of cytokines such as IL-10, IL-4, and IL-13. This balance of TH1/TH2 cytokine responses is believed to play an important role in coordinating an effective immune response, even under inflammatory conditions, although very limited data exist on their roles in sickle cell VOC.This study thus hypothesizes that the balance between TH1- and TH2-type cytokines might explain the differences in clinical outcomes in sickle cell disease. It was undertaken with patients with SCD in VOC in Zaria, Nigeria, a town in the zone of sickle cell endemicity of West Africa (17). The study analyzed numerical values for CD3⁺, CD4⁺, and CD8⁺ T cells and levels of selected serum cytokines in patients in VOC, and it compared these values with those obtained for steady-state SCD patients and unaffected hemoglobin AA homozygotes who served as normal healthy controls (NHC). This was done in an effort to understand if any imbalance in the immune response is important in the pathogenesis of sickle cell disease.     

Helicobacter pylori infection in sickle cell disease

Abdominal pain is a common presenting symptom in adults with sickle cell disease (SCD). One case of Helicobacter pylori gastritis has been reported in a child with sickle cell anemia. H. pylori-induced peptic ulcer disease (PUD) has not previously been reported in adults with SCD. We report eight cases of H. pylori infection in adult sickle cell patients presenting with acute or recurrent abdominal pain and/or gastrointestinal bleeding. In all cases, H. pylori serology (IgG) was positive, and three patients had gastric or duodenal ulcer by endoscopic examination. All patients responded to H. pylori treatment with complete resolution of symptoms by 4 weeks. The prevalence of H. pylori infection in SCD is unknown, but patients may be at increased risk for H. pylori-induced PUD and complications due to pre-existing anemia, increased nonsteroidal anti-inflammatory drug use, and alloimmunization which may delay necessary transfusion. It is important that the differential diagnosis of abdominal pain in adults with SCD include nonsickle cell-related disorders such as PUD. When confirmed, a definitive etiology of PUD must be determined so that appropriate treatment strategies can be initiated promptly and excess morbidity avoided.     

Bone Marrow Transplantation after Nonmyeloablative Treosulfan Conditioning Is Curative in a Murine Model of Sickle Cell Disease

Allogeneic hematopoietic stem cell transplantation (HSCT) can be curative for patients with sickle cell disease (SCD). However, morbidity associated with myeloablative conditioning and graft-versus-host disease has limited its utility. To this end, autologous HSCT for SCD using lentiviral gene-modified bone marrow (BM) or peripheral blood stem cells has been undertaken, although toxicities of fully ablative conditioning with busulfan and incomplete engraftment have been encountered. Treosulfan, a busulfan analog with a low extramedullary toxicity profile, has been used successfully as part of a myeloablative conditioning regimen in the allogeneic setting in SCD. To further minimize toxicity of conditioning, noncytotoxic monoclonal antibodies that clear stem cells from the marrow niche, such as anti-c-Kit (ACK2), have been considered. Using a murine model of SCD, we sought to determine whether nonmyeloablative conditioning followed by transplantation with syngeneic BM cells could ameliorate the disease phenotype. Treosulfan and ACK2, in a dose-dependent manner, decreased BM cellularity and induced cytopenia in SCD mice. Conditioning with treosulfan alone at nonmyeloablative dosing (3.6?g/kg), followed by transplantation with syngeneic BM donor cells, permitted long-term mixed-donor chimerism. Level of chimerism correlated with improvement in hematologic parameters, normalization of urine osmolality, and improvement in liver and spleen pathology. Addition of ACK2 to treosulfan conditioning did not enhance engraftment. Our data suggests that pretransplant conditioning with treosulfan alone may allow sufficient erythroid engraftment to reverse manifestations of SCD, with clinical application as a preparative regimen in SCD patients undergoing gene-modified autologous HSCT.     

HLA-B35 is associated with red cell alloimmunization in sickle cell disease

HLA-A, -B, -C, and DR antigens were determined in 33 patients with sickle cell disease (SCD), who had received red blood cell (RBC) transfusions. Twenty-one patients formed red cell alloantibodies after transfusions (responders) while 12 multitransfused SCD patients did not form any RBC antibodies (non-responders). We found that 67% of the SCD responder participants had HLA-B35 versus 25% of the non-responders (chi 2 = 5.3079, P = 0.0212). The frequency of B35 in non-responder SCD patients was similar to that of a normal healthy Black population consisting of 139 individuals. Calculation of the relative risk showed that sickle cell patients with B35 are six times more likely to form RBC alloantibodies after transfusion than those lacking that HLA antigen. We found no significant increase or association between any HLA-DR antigens and sickle cell disease.     

Common variable immunodeficiency and autoimmunity – an inconvenient truth

Coexisting morbidities in CVID include bronchiectasis, autoimmunity and malignancies. The incidence of autoimmune disease in CVID patients may approach 20% of cases. The most common autoimmune disease found in CVID patients is autoimmune cytopenia, but rheumatoid arthritis, lupus, and now primary biliary cirrhosis have also been reported. The coexistence of immunodeficiency and autoimmunity appears paradoxical, since one represents a hypoimmune state and the other a hyperimmune state. However, this paradox may not actually be all that implausible due to the complex nature of immune cells, signaling pathways and their interactions. The cellular alterations in combined variable immunodeficiency include a range of T and B cell abnormalities. Selective immune derangements found in CVID include a downregulation of regulatory T cells (Treg cells), accelerated T cell apoptosis, abnormal cytokine production secondary to cytokine gene polymorphisms and increased autoreactive B cell production. The impact of these abnormalities on T and B cell interaction may not only explain the immunodeficiency but also the development of autoimmunity in select groups of patients with CVID. The variability in the clinical manifestations of CVID as a result of this immune interaction suggests that CVID is not one disease but many. This is important because it follows that the treatment of CVID may not always be the same, but may need to be directed specifically towards each individual patient.     

Duffy phenotype does not influence the clinical severity of sickle cell disease

The red blood cell Duffy antigen receptor for chemokines serves as a sink for the clearance of chemokines such as interleukin-8 (IL-8) from the circulation. We analyzed the impact of the Duffy phenotype on sickle cell disease (SCD) severity and serum IL-8 levels in 15 Duffy-positive and 36 Duffy-negative sickle cell patients. There was no difference in clinical severity between Duffy-positive and Duffy-negative sickle cell patients. In asymptomatic sickle cell patients the upward deviation of mean serum IL-8 levels was significantly greater in Duffy-negatives (n = 20) than in Duffy-positives (n = 8) (P = 0.011). However, during a vasoocclusive episode, serum IL-8 levels were similar between Duffy-negatives (n = 11) and Duffy-positives (n = 3). Although the Duffy phenotype seems to influence steady-state serum IL-8 levels, it does not seem to have an effect on SCD severity.     

The 844ins68 cystathionine beta-synthase and C677T MTHFR gene polymorphism and the vaso-occlusive event risk in sickle cell disease

Introduction

Sickle cell disease (SCD) is an inflammatory condition with an increase in the adhesion of sickled erythrocytes, and it is a potential cause of vaso-occlusive episodes, an event related to clinical manifestations, morbidity and mortality. The cystathionine beta-synthase enzyme gene (CBS) and the methylenetetrahydrofolate reductase enzyme gene (MTHFR) are risk factors for thromboembolic disorders. This study evaluated the frequency of the 844ins68 CBS and C677T MTHFR gene polymorphisms and their possibility to be risk factors for vaso-occlusive crises.

Material and methods

In total 91 blood samples from SCD patients were studied by PCR-RFLP and PCR-allele-specific, for the SCD genotype confirmation and polymorphism identification.

Results

The presence of clinical manifestations related to vaso-occlusive crises were more frequent among patients with the Hb SS genotype (p = 0.007). The CBS enzyme gene was three times more frequent (p = 0.011) among patients with vaso-occlusive complications. The MTHFR gene mutation frequency showed no increased risk for vaso-occlusive crises in SCD patients (p = 0.193). The interaction between the two polymorphisms was evaluated in 12.08% of the SCD patients and doubled the vaso-occlusive disease risk (relative risk: 2.16).

Conclusions

We conclude that the presence of 844ins68 CBS and C677T MTHFR gene polymorphism was a risk factor for vaso-occlusive episodes in the SCD patients evaluated.     

Alternative complement pathway activity in sera from patients with sickle cell disease.

The low molecular weight cobra venom factor (CoVF) was used to activate the terminal sequence of the alternative complement pathway in thirty-one sera from patients with sickle cell disease (SCD). The SCD sera were compared with normal sera as a source of the alternative complement pathway factors C3 proactivator (C3PA) and C3PA convertase. These factors are required for formation of the enzymatically active CoVF-C3PA complex which is capable of cleaving C3 and thus initiating generation of the cytolytic C5b-9 complex. CoVF cofactor activity was significantly less than normal in SCD sera as measured in an indirect lysis assay, indicating reduced C3PA or C3PA convertase activity in these sera. Qualitative (immunoelectrophoresis) and quantitative (radial immunodiffusion) measurement of C3PA showed, however, that this protein is normal or elevated in SCD sera. Taken together, the reduced CoVF cofactor activity and normal or elevated C3PA in SCD sera suggests that sera from patients with sickle cell disease have reduced C3PA convertase activity.