Non-parasitized Red Blood Cells Research Articles

Mechanisms Underlying the Effects of Chloroquine on Red Blood Cells Metabolism.

Chloroquine (CQ) is a 4-aminoquinoline derivative largely employed in the management of malaria. CQ treatment exploits the drug's ability to cross the erythrocyte membrane, inhibiting heme polymerase in malarial trophozoites. Accumulation of CQ prevents the conversion of heme to hemozoin, causing its toxic buildup, thus blocking the survival of Plasmodium parasites. Recently, it has been reported that CQ is able to exert antiviral properties, mainly against HIV and SARS-CoV-2. This renewed interest in CQ treatment has led to the development of new studies which aim to explore its side effects and long-term outcome. Our study focuses on the effects of CQ in non-parasitized red blood cells (RBCs), investigating hemoglobin (Hb) functionality, the anion exchanger 1 (AE1) or band 3 protein, caspase 3 and protein tyrosine phosphatase 1B (PTP-1B) activity, intra and extracellular ATP levels, and the oxidative state of RBCs. Interestingly, CQ influences the functionality of both Hb and AE1, the main RBC proteins, affecting the properties of Hb oxygen affinity by shifting the conformational structure of the molecule towards the R state. The influence of CQ on AE1 flux leads to a rate variation of anion exchange, which begins at a concentration of 2.5 μM and reaches its maximum effect at 20 µM. Moreover, a significant decrease in intra and extracellular ATP levels was observed in RBCs pre-treated with 10 µM CQ vs. erythrocytes under normal conditions. This effect is related to the PTP-1B activity which is reduced in RBCs incubated with CQ. Despite these metabolic alterations to RBCs caused by exposure to CQ, no signs of variations in oxidative state or caspase 3 activation were recorded. Our results highlight the antithetical effects of CQ on the functionality and metabolism of RBCs, and encourage the development of new research to better understand the multiple potentiality of the drug.

Potential Role of Chloroquine in Macrophageal Iron Mobilization

Malaria anaemia is still a major killer of children in malaria endemic countries. We have shown from the published literature that malaria anaemia, especially mild to moderate anaemia is largely due to inflammation-induced hypoferreamia and immune-mediated destruction of parasitized and non-parasitized red blood cells. In this review, we speculate that the immunomodulatory and anti-inflammatory properties of chloroquine, a cheap, readily available antimalarial, may make it a very good candidate for investigation as a possible adjunct treatment for malariaassociated anaemia.

Plasmodium falciparum, but not P. vivax, can induce erythrocytic apoptosis.

BackgroundApoptosis can occur in red blood cells (RBC) and seems to be involved in hematologic disorders related to many diseases. In malaria it is known that parasitized RBC (pRBC) is involved in the development of anemia and thrombosis; however, non-parasitized RBC (nRBC) apoptosis could amplify these malaria-associated hematologic events. In fact, in experimental malaria, increased levels of apoptosis were observed in nRBC during lethal Plasmodium yoelii 17XL infection, but in human malaria erythrocytic apoptosis has never been studied. The present study was performed to investigate if nRBC apoptosis also occurs in P. vivax and P. falciparum infections.FindingsApoptosis of nRBC was evaluated in blood samples of P. vivax malaria patients and clinically healthly individuals living in Manaus, Brazil, both ex vivo and after incubation of RBC for 24 h. Additionally, the capacity of plasma from P. vivax or P. falciparum patients was tested for induction of in vitro apoptosis of normal RBC from a clinically healthy individual living in a non-endemic malaria region. Apoptosis was detected by flow cytometry using annexin V staining. In contrast to experimental malaria that significantly increased the levels of apoptotic nRBC both ex-vivo and after 24 h of incubation, no significant alteration on apoptotic nRBC rates was detected in P. vivax infected patients when compared with non-infected control individuals. Similar results were observed when plasma of these P. vivax patients was incubated with normal RBC. Conversely, plasma from P. falciparum-infected subjects induced significant apoptosis of these cells.ConclusionsApoptosis of normal RBC can be induced by plasma from individuals with P. falciparum (but not with P. vivax) malaria. This finding could reflect the existence of erythrocytic apoptosis during infection that could contribute to the pathogenesis of hematological and vascular complications associated with falciparum malaria.

Rare‐Cell Enrichment by a Rapid, Label‐Free, Ultrasonic Isopycnic Technique for Medical Diagnostics

One significant challenge in medical diagnostics lies in the development of label-free methods to separate different cells within complex biological samples. Here we demonstrate a generic, low-power ultrasonic separation technique, able to enrich different cell types based upon their physical properties. For malaria, we differentiate between infected and non-infected red blood cells in a fingerprick-sized drop of blood. We are able to achieve an enrichment of circulating cells infected by the ring stage of the parasite over nonparasitized red blood cells by between two and three orders of magnitude in less than 3 seconds (enabling detection at parasitemia levels as low as 0.0005 %). In a second example, we also show that our methods can be used to enrich different cell types, concentrating Trypanosoma in blood at very low levels of infection, on disposable, low-cost chips.

Rare‐Cell Enrichment by a Rapid, Label‐Free, Ultrasonic Isopycnic Technique for Medical Diagnostics

AbstractOne significant challenge in medical diagnostics lies in the development of label‐free methods to separate different cells within complex biological samples. Here we demonstrate a generic, low‐power ultrasonic separation technique, able to enrich different cell types based upon their physical properties. For malaria, we differentiate between infected and non‐infected red blood cells in a fingerprick‐sized drop of blood. We are able to achieve an enrichment of circulating cells infected by the ring stage of the parasite over nonparasitized red blood cells by between two and three orders of magnitude in less than 3 seconds (enabling detection at parasitemia levels as low as 0.0005 %). In a second example, we also show that our methods can be used to enrich different cell types, concentrating Trypanosoma in blood at very low levels of infection, on disposable, low‐cost chips.

Plasmodium falciparum , but not P. vivax , can induce erythrocytic apoptosis

Apoptosis can occur in red blood cells (RBC) and seems to be involved in hematologic disorders related to many diseases. In malaria it is known that parasitized RBC (pRBC) is involved in the development of anemia and thrombosis; however, non-parasitized RBC (nRBC) apoptosis could amplify these malaria-associated hematologic events. In fact, in experimental malaria, increased levels of apoptosis were observed in nRBC during lethal Plasmodium yoelii 17XL infection, but in human malaria erythrocytic apoptosis has never been studied. The present study was performed to investigate if nRBC apoptosis also occurs in P. vivax and P. falciparum infections. Apoptosis of nRBC was evaluated in blood samples of P. vivax malaria patients and clinically healthly individuals living in Manaus, Brazil, both ex vivo and after incubation of RBC for 24 h. Additionally, the capacity of plasma from P. vivax or P. falciparum patients was tested for induction of in vitro apoptosis of normal RBC from a clinically healthy individual living in a non-endemic malaria region. Apoptosis was detected by flow cytometry using annexin V staining. In contrast to experimental malaria that significantly increased the levels of apoptotic nRBC both ex-vivo and after 24 h of incubation, no significant alteration on apoptotic nRBC rates was detected in P. vivax infected patients when compared with non-infected control individuals. Similar results were observed when plasma of these P. vivax patients was incubated with normal RBC. Conversely, plasma from P. falciparum-infected subjects induced significant apoptosis of these cells. Apoptosis of normal RBC can be induced by plasma from individuals with P. falciparum (but not with P. vivax) malaria. This finding could reflect the existence of erythrocytic apoptosis during infection that could contribute to the pathogenesis of hematological and vascular complications associated with falciparum malaria.

Hepatic dysfunction in falciparum malaria in West Bengal”.

Aims and objectives: Malaria, a devastating tropical disease, is very common in India and native countries. In West Bengal, the influence of falciparum and vivax malaria is so high, that each year, many people are affected by these parasites. Our aim is to evaluate the amount of hepatic dysfunction in case of plasmodium affected patients. Materials and methods: In clinically diagnosed 108 patients, admitted in our hospital in the years 2010- 2013, confirmation were done thick and thin blood film and/or serology. After diagnosis, other hematological, serological and biochemical tests were carried out other diseases responsible for hepatitis. Then we compared bilirubin, SGOT, SGPT, alkaline phosphatase and hemoglobin as well as correlation between bilirubin and hemoglobin and liver enzymes amongst males (n=62) and females (n=46). Results: Mean values of bilirubin, SGPT and SGOT were significantly raised in males than females. Bilirubin showed significant positive correlation with SGPT and alkaline phosphatase and negative correlation with hemoglobin in both sexes, but positive correlation with males. Conclusion: Plasmodium falciparum was mainly responsible for hepatic dysfunction in the form of raised liver enzymes rather than only hyperbilirubinemia due to ruptured parasitized or nonparasitized red blood cells (RBC). In future, large scale studies are required justify the above correlations.

Simultaneous determination of phagocytosis of Plasmodium falciparum-parasitized and non-parasitized red blood cells by flow cytometry

BackgroundSevere falciparum malaria anaemia (SMA) is a frequent cause of mortality in children and pregnant women. The most important determinant of SMA appears to be the loss of non-parasitized red blood cells (np-RBCs) in excess of loss of parasitized (p-) RBCs at schizogony. Based on data from acute SMA where excretion of haemoglobin in urine and increased plasma haemoglobin represented respectively less than 1% and 0.5% of total Hb loss, phagocytosis appears to be the predominant mechanism of removal of np- and p-RBC.Estimates indicate that np-RBCs are cleared in approximately 10-fold excess compared to p-RBCs. An even larger removal of np-RBCs has been described in vivax malaria anaemia. Estimates were based on two single studies both performed on neurosyphilitic patients who underwent malaria therapy. As the share of np-RBC removal is likely to vary between wide limits, it is important to assess the contribution of both np- and p-RBC populations to overall RBC loss, and disclose the mechanism of such variability. As available methods do not discriminate between the removal of np- vs p-RBCs, the purpose of this study was to set up a system allowing the simultaneous determination of phagocytosis of p- and np-RBC in the same sample.Methods and ResultsPhagocytosis of p- and np-RBCs was quantified in the same sample using double-labelled target cells and the human phagocytic cell-line THP-1, pre-activated by TNF and IFNγ to enhance their phagocytic activity. Target RBCs were double-labelled with fluorescent carboxyfluorescein-succinimidyl ester (CF-SE) and the DNA label ethidium bromide (EB). EB, a DNA label, allowed to discriminate p-RBCs that contain parasitic DNA from the np-RBCs devoid of DNA. FACS analysis of THP-1 cells fed with double-labelled RBCs showed that p- and np-RBCs were phagocytosed in different proportions in relation to parasitaemia.ConclusionsThe assay allowed the analysis of phagocytosis rapidly and with low subjective error, and the differentiation between phagocytosed p- and np-RBCs in the same sample. The presented method may help to analyse the factors or conditions that modulate the share of np-RBC removal in vitro and in vivo and lead to a better understanding of the pathogenesis of SMA.

Transfer of 4‐hydroxynonenal from parasitized to non‐parasitized erythrocytes in rosettes. Proposed role in severe malaria anemia

Severe anaemia is a life-threatening complication of falciparum malaria associated with loss of predominantly non-parasitized red blood cells (npRBCs). This poorly elucidated process might be influenced by (i) rosettes, i.e. npRBCs cytoadherent to haemozoin-containing parasitized RBCs (pRBCs) and (ii) generation in pRBCs of 4-hydroxynonenal (4-HNE) through haemozoin-catalysed lipid peroxidation. We explored whether close proximity in rosettes may facilitate 4-HNE transfer to npRBCs, which is likely to enhance their phagocytosis and contribute to malaria anaemia. Fluorescence microscopy and flow cytometry data indicated 4-HNE transfer to npRBCs in rosettes. Rosettes were formed by 64·8 ± 1·8% varO-expressing pRBCs, and 8·7 ± 1·1% npRBCs were positive for 4-HNE-protein-conjugates, while low-rosetting parasites generated only 2·4 ± 1·1% 4-HNE-conjugate-positive npRBCs. 4-HNE transfer decreased after blocking rosetting by monoclonal antibodies. A positive linear relationship between rosette frequency and 4-HNE-conjugates in npRBCs was found in 40 malaria patients, a first indication for a role of rosetting in npRBCs modifications in vivo. Children with severe malaria anaemia had significantly higher percentages of 4-HNE-conjugate-positive npRBCs compared to children with uncomplicated malaria. In conclusion, 4-HNE transfer from pRBCs to npRBCs in rosettes is suggested to play a role in the phagocytic removal of large numbers of npRBCs, the hallmark of severe malaria anaemia.

Refractoriness of Eryptotic Red Blood Cells to Plasmodium falciparum Infection: A Putative Host Defense Mechanism Limiting Parasitaemia

Recently, we have described that apoptosis-like process of red blood cells (RBC) – eryptosis – in malaria is not restricted to parasitized cells, occurring also in non-parasitized RBC (nRBC). Besides to pathogenic proprieties, apoptosis also participates in the innate defense trough restriction of intracellular pathogens propagation. In the present study, we investigated the capacity of P. falciparum parasites to infect eryptotic RBC. Schizont parasitized RBC concentrated by magnetic separation were cultured with eryptotic RBC obtained by ionomycin treatment and, then, parasite growth was evaluated in Giemsa-stained thin blood smears. While parasites infected and developed normally in control non-eryptotic RBC, cultures performed with eryptotic RBC had a marked decrease in parasitaemia. It was noteworthy a great number of free merozoites in eryptotic RBC cultures, indicating that these cells were not susceptible to invasion. We suggest that although eryptosis could be involved in malaria pathogenesis, it could also acting protectively by controlling parasite propagation.

A Role for Fetal Hemoglobin and Maternal Immune IgG in Infant Resistance to Plasmodium falciparum Malaria

BackgroundIn Africa, infant susceptibility to Plasmodium falciparum malaria increases substantially as fetal hemoglobin (HbF) and maternal immune IgG disappear from circulation. During the first few months of life, however, resistance to malaria is evidenced by extremely low parasitemias, the absence of fever, and the almost complete lack of severe disease. This resistance has previously been attributed in part to poor parasite growth in HbF-containing red blood cells (RBCs). A specific role for maternal immune IgG in infant resistance to malaria has been hypothesized but not yet identified.Methods and FindingsWe found that P. falciparum parasites invade and develop normally in fetal (cord blood, CB) RBCs, which contain up to 95% HbF. However, these parasitized CB RBCs are impaired in their binding to human microvascular endothelial cells (MVECs), monocytes, and nonparasitized RBCs – cytoadherence interactions that have been implicated in the development of high parasite densities and the symptoms of malaria. Abnormal display of the parasite's cytoadherence antigen P. falciparum erythrocyte membrane protein-1 (PfEMP-1) on CB RBCs accounts for these findings and is reminiscent of that on HbC and HbS RBCs. IgG purified from the plasma of immune Malian adults almost completely abolishes the adherence of parasitized CB RBCs to MVECs.ConclusionsOur data suggest a model of malaria protection in which HbF and maternal IgG act cooperatively to impair the cytoadherence of parasitized RBCs in the first few months of life. In highly malarious areas of Africa, an infant's contemporaneous expression of HbC or HbS and development of an immune IgG repertoire may effectively reconstitute the waning protective effects of HbF and maternal immune IgG, thereby extending the malaria resistance of infancy into early childhood.

Severe Malarial Anemia: Innate Immunity and Pathogenesis

Greater than 80% of malaria-related mortality occurs in sub-Saharan Africa due to infections with Plasmodium falciparum. The majority of P. falciparum-related mortality occurs in immune-naïve infants and young children, accounting for 18% of all deaths before five years of age. Clinical manifestations of severe falciparum malaria vary according to transmission intensity and typically present as one or more life-threatening complications, including: hyperparasitemia; hypoglycemia; cerebral malaria; severe malarial anemia (SMA); and respiratory distress. In holoendemic transmission areas, SMA is the primary clinical manifestation of severe childhood malaria, with cerebral malaria occurring only in rare cases. Mortality rates from SMA can exceed 30% in pediatric populations residing in holoendemic transmission areas. Since the vast majority of the morbidity and mortality occurs in immune-naïve African children less than five years of age, with SMA as the primary manifestation of severe disease, this review will focus primarily on the innate immune mechanisms that govern malaria pathogenesis in this group of individuals. The pathophysiological processes that contribute to SMA involve direct and indirect destruction of parasitized and non-parasitized red blood cells (RBCs), inefficient and/or suppression of erythropoiesis, and dyserythropoiesis. While all of these causal etiologies may contribute to reduced hemoglobin (Hb) concentrations in malaria-infected individuals, data from our laboratory and others suggest that SMA in immune-naïve children is characterized by a reduced erythropoietic response. One important cause of impaired erythroid responses in children with SMA is dysregulation in the innate immune response. Phagocytosis of malarial pigment hemozoin (Hz) by monocytes, macrophages, and neutrophils is a central factor for promoting dysregulation in innate inflammatory mediators. As such, the role of P. falciparum-derived Hz (PfHz) in mediating suppression of erythropoiesis through its ability to cause dysregulation in pro- and anti-inflammatory cytokines, growth factors, chemokines, and effector molecules is discussed in detail. An improved understanding of the etiological basis of suppression of erythropoietic responses in children with SMA may offer the much needed therapeutic alternatives for control of this global disease burden.

Apoptosis of non-parasitized red blood cells in malaria: a putative mechanism involved in the pathogenesis of anaemia

BackgroundSevere anaemia is a common complication of Plasmodium falciparum malaria in hyperendemic regions. Premature elimination of non-parasitized red blood cells (nRBC) has been considered as one mechanism involved in the genesis of severe malaria anaemia. It has been reported that apoptosis can occur in RBC and, consequently, this cell death process could contribute to anaemia. This study was performed to evaluate the susceptibility of nRBC to apoptosis in a malaria anaemia murine model.MethodsBalb/c mice were intraperitonially inoculated with 1 × 106 P. yoelii 17XL parasitized RBC (pRBC) and, then, parasitaemia and anaemia were monitored. Apoptosis in both pRBC and nRBC was assessed during early and late phases of infection by flow cytometry using Syto 16 and annexin V-PE double staining and forward scatter measurement.ResultsAs expected, experimental infection of Balb/c mice with Plasmodium yoelii 17XL parasites was characterized by progressive increase of parasitaemia and acute anaemia, leading to death. Flow cytometry analysis showed that a number of pRBC was in the apoptotic process. It was noteworthy that the increase of nRBC apoptosis levels occurred in the late phase of infection, when anaemia degree was notably accentuated, while no significant alteration was observed in the early phase.ConclusionThe increased levels of nRBC apoptosis herein firstly reported, in malaria infection could represent a putative mechanism worsening the severity of malarial anaemia.

Plasmodium falciparum glycosylphosphatidylinositol toxin interacts with the membrane of non-parasitized red blood cells: a putative mechanism contributing to malaria anemia

Following exposure to synthetic Plasmodium falciparum glycosylphosphatidylinositol (P.f.-GPI), red blood cells (RBCs) reacted with antibodies in the serum of a patient with severe acute P. falciparum malaria. Carbohydrate microarray analysis of the patient's serum confirmed the presence of both, IgM and IgG antibodies against P.f.-GPI. The antibodies failed to bind to RBCs when P.f.-GPI lacking the lipid portion was applied. Addition of the detergent Triton X-100 during preincubation with P.f.-GPI resulted in increased recognition. Recognition of P.f.-GPI was dependent on the concentrations of synthetic P.f.-GPI, the serum and the numbers of RBCs. IgM antibodies dominated P.f.-GPI-sensitized RBCs recognition. Recognition by IgM antibodies proved highest during the 1stweek of acute malaria and decreased during the following 2weeks as assessed by flow cytometry and carbohydrate microarray analysis. These results strongly support the notion that released P.f.-GPI can insert into non-parasitized RBC membranes and results in recognition by circulating anti-GPI antibodies and possibly subsequent elimination. This process may contribute to malaria-associated anemia.

Concentration and purification by magnetic separation of the erythrocytic stages of all human Plasmodium species

BackgroundParasite concentration methods facilitate molecular, biochemical and immunological research on the erythrocytic stages of Plasmodium. In this paper, an adaptation of magnetic MACS® columns for the purification of human Plasmodium species is presented. This method was useful for the concentration/purification of either schizonts or gametocytes.Results and conclusionsThe magnetic removal of non-parasitized red blood cells (in vivo and in vitro) using magnetic columns (MACS) was evaluated. This easy-to-use technique enriched schizonts and gametocytes from Plasmodium falciparum in vitro cultures with a very high degree of purity. In addition, all haemozoin-containing stages (schizonts and/or gametocytes) from the peripheral blood of infected patients could be concentrated using this method. This method is particularly useful for the concentration of non-falciparum species, which do not grow in culture and are otherwise difficult to obtain in large amounts.

Massive Destruction of Malaria-Parasitized Red Blood Cells despite Spleen Closure

It is currently accepted that malaria-parasitized red blood cells (pRBC) are eliminated, like senescent erythrocytes, phagocytically by macrophages in the red pulp of the spleen. Here, however, we show that self-healing Plasmodium chabaudi malaria activates spleen closure in C57BL/6 mice. Confocal laser scanning microscopy revealed that spleen closing was manifested by elimination of entry into the red pulp of 3-microm polystyrol particles, pRBC, and nonparasitized red blood cells but not of bovine serum albumin. This spleen closure did not reflect a reduction in the number of phagocytic cells, as shown by flow cytometry, whereas marginal zone macrophages (MZM) were lost and red pulp macrophages entered the white pulp. Splenic trapping of pBRC was strongly reduced in the absence of MZM and marginal metallophilic macrophages (MMM), as it is in noninfected mice with a disrupted lymphotoxin beta receptor (LTbetaR(-/-)), and it was still significantly reduced when the number of MZM and MMM was diminished, as in tumor necrosis factor alpha-deficient (TNF-alpha(-/-)) mice. Moreover, mice deficient in TNF-alpha, tumor necrosis factor receptor I (TNFRI(-/-)), and LTbetaR exhibited progressive impairment in malaria-induced spleen closing. Treatment of C57BL/6 mice with TNF-alpha induced loss of MZM and spleen closing by about 20%. Our data indicate that TNF/TNFRI signaling is involved in regulating malaria-induced spleen closure, which is maximal during crisis, when parasitemia declines more than 100-fold. Consequently, the vast majority of pRBC cannot be destroyed by the spleen during crisis, suggesting that the known sophisticated sequestration system of Plasmodium parasites did not evolve to avoid splenic clearance.

Carrier-mediated partitioning of artemisinin into Plasmodium falciparum-infected erythrocytes.

The purpose of the present study was to characterize the partitioning of artemisinin into both uninfected and Plasmodium falciparum-infected red blood cells (RBCs). The partitioning of [(14)C](+)-artemisinin into RBCs was studied at four different hematocrit levels and eight time periods. At the optimum time of 2 h, the partitioning process was investigated with eight different drug concentrations ranging from 0.88 to 3.52 microM at 37 and 4 degrees C. The effect of the presence of unlabeled artemisinin on the partitioning of the same concentration of [(14)C]artemisinin was studied. About 35 to 40% of the drug was seen to partition into uninfected RBCs at a hematocrit of 33%, irrespective of the incubation period or the drug concentration used. In contrast, infected RBCs showed an increase in partitioning of the drug with time until saturation was achieved at 1 h. While the partitioning of artemisinin into parasitized RBCs at 37 degrees C was found to be significantly higher than that in nonparasitized RBCs, at 4 degrees C both parasitized and nonparasitized RBCs showed identical partitioning of the drug. The partitioning of [(14)C]artemisinin into parasitized RBCs was completely inhibited in the presence of the same concentration of unlabeled artemisinin. However, no such effect was observed in nonparasitized cells, and no evidence suggesting that binding of the drug in parasitized RBCs is reversible was found. The partitioning of artemisinin into parasitized RBCs was found to be rapid, saturable, temperature dependent, irreversible, and subject to competitive inhibition with unlabeled artemisinin. The results obtained suggest the involvement of carrier mediation in the partitioning of artemisinin across the parasitized RBC membrane. In contrast, simple passive diffusion of artemisinin was seen in nonparasitized RBCs.

In vitro inhibition of Plasmodium falciparum merozoite invasion by human plasma fibronectin.

Human fibronectin isolated from citrated blood was tested for its ability to bind to Plasmodium falciparum by an indirect immunofluorescent assay using rabbit antiserum to human fibronectin. A positive reaction was observed on merozoites inside schizont-infected erythrocytes. The binding was not observed on non-parasitized red blood cells. The effect of human fibronectin on P. falciparum growth was further studied using an in vitro inhibition assay; 50% inhibition of parasite multiplication was obtained with approximately 100 micrograms/ml of human fibronectin. Slight inhibition was observed below 10 micrograms/ml. The significance of this finding is discussed.

Expression of cell-mediated antimicrobial immunity by mouse trophoblast monolayers.

Monolayers of mouse trophoblast cells were produced after short-term culture (two to four days) of ectoplacental cone cells derived from 7.5-day-old mouse conceptuses and were then tested for phagocytic activity. Following brief intervals of coincubation with the blood stage form of Plasmodium berghei, the parasite that causes rodent malaria, cultured trophoblast cells were found to phagocytose large amounts of parasitic material. In a manner similar to that of peritoneal macrophages, trophoblast cells ingested predominantly hemozoin pigment granules, while internalization of nonparasitized red blood cells occurred infrequently. Trophoblast-mediated phagocytosis was sensitive to the inhibitory effects of cytochalasin B. The expression of this form of immunelike function by midstage trophoblastic elements may play an important role during embryogenesis by protecting the fetoplacental unit from injury by invading microorganisms or by limiting congenitally acquired infections.