Experimental acute Babesia caballi infections: I. Red blood cell dynamics

Hematological determinations were made on blood samples from six ponies acutely infected with two dosage levels of Babesia caballi (Group 1: divided into two subgroups of three ponies each). Similar determinations were made on blood samples from three premunized ponies given challenge inoculations (Group 2), and three equidae given uninfected red blood cells (Group 3).A trend towards decreases in RBC counts, hemoglobin concentrations, and hematocrits within one to four days after inoculation (AI) was observed in all groups. However, it was marked only in Group 1. In addition, only in Group 1 was there observed a concerted anemia occurring between Days 7 and 16.Those surviving ponies in Group 1 which developed a higher parasitemia between Days 5 and 6 AI (first parasitemia peak) developed a more severe anemia between Days 7 and 16. Ponies which developed parasitemias higher than 40 × 10³ parasitized cells/mm³ at the first parasitemia peak subsequently died.Free bilirubin in Group 1 animals increased immediately after inoculation, and repeatedly exceeded normal ranges until after Day 20 AI when the RBC counts were rising. Similar changes in free bilirubin did not occur in either Groups 2 or 3. Conjugated bilirubin levels did not exceed normal ranges in any of the experimental animals.Active erythrophagocytosis was evident in histological preparations of lymph node, spleen, liver, and lung from ponies which died. Cytosiderin pigment was present in liver parenchyma, and hematin was scattered throughout lymph nodes and spleen.     

Homeostasis of extracellular ATP in uninfected RBCs from a Plasmodium falciparum culture and derived microparticles

Plasmodium falciparum, a dangerous parasitic agent causing malaria, invades human red blood cells (RBCs), causing hemolysis and microvascular obstruction. These and other pathological processes of malaria patients are due to metabolic and structural changes occurring in uninfected RBCs. In addition, infection activates the production of microparticles (MPs).ATP and byproducts are important extracellular ligands modulating purinergic signaling within the intravascular space.Here, we analyzed the contribution of uninfected RBCs and MPs to the regulation of extracellular ATP (eATP) of RBCs, which depends on the balance between ATP release by specific transporters and eATP hydrolysis by ectonucleotidases.RBCs were cultured with P. falciparum for 24–48 h prior to experiments, from which uninfected RBCs and MPs were purified. On-line luminometry was used to quantify the kinetics of ATP release. Luminometry, colorimetry and radioactive methods were used to assess the rate of eATP hydrolysis by ectonucleotidases. Rates of ATP release and eATP hydrolysis were also evaluated in MPs.Uninfected RBCs challenged by different stimuli displayed a strong and transient activation of ATP release, together with an elevated rate of eATP hydrolysis. MPs contained ATP in their lumen, which was released upon vesicle rupture, and were able to hydrolyze eATP.Results suggest that uninfected RBCs and MPs can act as important determinants of eATP regulation of RBCs during malaria.The comparison of eATP homeostasis in infected RBCs, ui-RBCs, and MPs allowed us to speculate on the impact of P. falciparum infection on intravascular purinergic signaling and the control of the vascular caliber by RBCs.     

Vaccination of lambs against Haemonchus contortus infection with a somatic protein (Hc23) from adult helminths

A somatic protein from adult Haemonchus contortus (Hc23), the most abundant component in a low molecular weight fraction with known immunizing effect against experimental haemonchosis, has been purified by immunochromatography. The immunoprophylactic value of Hc23 was tested in groups of 5–6 months old Assaf lambs using Al(OH)₃ or Escherichia coli lipopolysaccharide + inactivated Propionibacterium acnes as adjuvant and the results compared with uninfected control, uninfected and challenged or infected and challenged lambs. Immunization with Hc23 in either adjuvant elicited significant reductions in fecal egg counts after challenge with 15,000 L3s (70.67%–85.64%, respectively) and reduced (67.1% and 86%) abomasal worm counts (45 days post-challenge). Immunized lambs displayed higher peripheral eosinophil counts, were less anaemic and had weight gains than challenged controls. The results suggest that the Hc23 antigen can induce a partially protective response against haemonchosis in lambs.     

Trypanosoma musculi: Passive hemagglutination technique to measure antibody in mice

A passive hemagglutination assay was developed to measure Trypanosoma musculi-specific antibody in mice. Indicator-erythrocyte donor mice received 550 rad ⁶⁰Co 24 hr before intraperitoneal injection of 3 × 10⁴T. musculi. T. musculi antigen-coated erythrocytes were obtained from these mice on Day 9 postinfection. T. musculi antigen-coated erythrocytes obtained in this manner were used as indicator erythrocytes in a passive hemagglutination procedure. Serum from hyperimmunized mice (three consecutive infections at 21-day intervals) gave titers as high as 1:1024. Titers of 1:256 and 1:512 were obtained from singly infected mice on Days 18 and 28 postinfection, respectively. In marked contrast, nude mice infected with T. musculi did not produce a detectable agglutinating antibody response. Erythrocytes obtained from either irradiated (550 rad ⁶⁰Co) uninfected mice, nonirradiated infected mice, or normal mice did not agglutinate when combined with any of the sera tested. These data suggest the usefulness of this passive hemagglutination assay for the measurement of antibody to T. musculi in the serum of infected mice.     

A primary Corynebacterium pseudotuberculosis low dose infection in alpacas (Lama pacos) protects against a lethal challenge exposure

Corynebacterium pseudotuberculosis is the agent of alpaca's lymphadenitis. The present study was to demonstrate the effect of a primary infection with low (1.1 × 10³), moderate (1 × 10⁴), and high (1.2 × 10⁵) doses of C. pseudotuberculosis against a significant higher challenge dose of 9 × 10⁸ CFU of C. pseudotuberculosis. Three groups of 4 healthy male alpacas were inoculated subcutaneously (SC) in the left flank behind the costal arch with the above doses of bacteria. A fourth group of 4 alpacas was sham inoculated with phosphate buffered saline as control. After 5 weeks all animals were challenged with a dose of 9 × 10⁸ CFU of C. pseudotuberculosis inoculated SC in the right flank. The alpacas were clinically inspected for local and regional abscesses, body temperature and behavior changes. The primary infected alpacas had a febrile response, and abscesses at the inoculation point and regional lymph nodes. However, after challenge, the primary infected animals showed no superficial lesions or febrile response. In contrast, the immune naïve alpacas from group D developed a severe disease characterized by fever, abscesses in regional lymphnodes, and in one alpaca a subcutaneous edema and sudden death 2 weeks after exposure. In addition, primary infected alpacas had a robust antibody response against C. pseudotuberculosis cell wall antigen with significant differences with respect the naïve challenged alpacas. At necropsy, the primary infected alpacas had abscesses only in the regional or internal renal-lymph nodes from the left or primary inoculation side of the body, with no lesions in the right challenged side. In contrast, the primary sham inoculated alpacas had abscesses in the regional and internal lymph nodes from the right challenged side. This work showed that a primary infection with at least 1.1 × 10³ viable C. pseudotuberculosis induces protection against a second high dose exposure to this bacterium. These results will be useful for further study of prevention methods to control lymphadenitis in alpacas.     

Counterregulation of Th2 immunity by interleukin 12 reduces host defenses against Strongyloides venezuelensis infection

The aim of this study was to investigate the role of interleukin 12 (IL-12) during Strongyloides venezuelensis infection. IL-12^−/− and wild-type C57BL/6 mice were subcutaneously infected with 1500 larvae of S. venezuelensis. On days 7, 14, and 21 post-infection, we determined eosinophil and mononuclear cell numbers in the blood and broncoalveolar lavage fluid (BALF), Th2 cytokine secretion in the lung parenchyma, and serum antibody levels. The numbers of eggs in the feces and worm parasites in the duodena were also quantified. The eosinophil and mononuclear cell counts and the concentrations of IL-3, IL-5, IL-10, IL-13, and IgG1 and IgE antibodies increased significantly in infected IL-12^−/− and wild-type mice as compared with uninfected controls. However, the number of eosinophils and mononuclear cells in the blood and BALF and the Th2 cytokine levels in the lungs of infected IL-12^−/− mice were greater than in infected wild-type C57BL/6 mice. In addition, serum IgE and IgG1 levels were also significantly enhanced in the infected mice lacking IL-12. Meanwhile, parasite burden and fecal egg counts were significantly decreased in infected IL-12^−/− mice. Together, our results showed that the absence of IL-12 upregulates the Th2 immune response, which is important for control of S. venezuelensis infection.     

Variations of glycoprotein IIb–IIIa (αIIb/β3-integrin) content in healthy donors. The influence on platelet aggregation activity and efficacy of aspirin action

The effects of content of a fibrinogen receptor, glycoprotein (GP) IIb–IIIa (αIIb/β3-integrin), GP IIIa genetic polymorphism (substitution Leu33Pro), and fibrinogen concentration in blood plasma on platelet aggregation activity have been investigated in a group of healthy volunteers. In 35 examined donors the GP IIb–IIIa content on platelet surface varied from 40 to 71 × 10³ per platelet. Repeated measurements revealed that the GP IIb–IIIa content coefficient of variation was 9.5%, and deviations from mean levels did not exceed 20%. The level and the rate of platelet aggregation induced by ADP (1.25–20 μM) correlated with GP IIb–IIIa number (r from 0.315 to 0.591) and were higher in the group of donors with high in comparison with low GP IIb–IIIa content (>60 and (40–50) × 10^?3 per platelet, respectively). Aspirin, the inhibitor of thromboxane A₂ synthesis, partially suppressed ADP-induced platelet aggregation. The level of residual aggregation in the presence of aspirin also correlated with GP IIb–IIIa content and increased in subjects with high receptor content. Parameters of ADP-induced aggregation did not differ in donors with genotypes GP IIIa Pro33(?) (Leu33Leu33, n = 20) and Pro33(+) (Leu33Pro33, n = 13, and Pro33Pro33, n = 2) genotype. GP IIb–IIIa content was also not affected by GP IIIa polymorphism. No significant correlations were found between the level and rate of platelet aggregation and fibrinogen concentration in blood plasma. The data obtained indicate that the effects of variations of GP IIb–IIIa content on platelet aggregation are higher than GP IIIa Leu33Pro polymorphism and variations of fibrinogen concentration. High GP IIb–IIIa content is associated with increased platelet aggregation activity and decreased efficacy of aggregation inhibition by aspirin.     

The interaction of Babesia caballi kinetes with tick cells

Babesia caballi caused pathological changes in the vector tick, Anocentor nitents. These included the loss of hemocytes, reddish-brown discoloration of the hemolymph, retardation in clotting, and reduction in egg production. Primary cultures were initiated from A. nitens embryos transovarially infected with B. caballi. Cell lines that were isolated were morphologically similar and composed of stellate, fusiform, and hemocyte-like cells, but none was visibly infected with B. caballi. Primary cultures from heavily infected ticks were not viable and did not develop into lines. Kinetes from hemolymph and organs of A. nitens were cocultivated with cell lines isolated from embryos of A. nitens, Rhipicephalus appendiculatus, and Rhipicephalus sanguineus. They attached to and actively penetrated the cells. Cells that were penetrated by or infected with B. caballi showed rounding off, degeneration, and lysis. In Giemsa-stained spreads prepared after 1 or 2 days in vitro, more kinetes were associated with R. appendiculatus cells when the medium contained A. nitens egg extract (TEE). Ninety percent of the B. caballi kinetes were always found within or in close contact with cells from A. nitens, cultured with or without TEE. The parasites were club shaped, amoeboid, or round. Intracellular Babesia were frequently lying adjacent to the host cell nucleus. In the cultures the parasites were detected by light microscopy for 3 to 5 days; they did not transform into other tick-associated stages and were not seen after 1 week. This is the first report of the cultivation of tick stages of B. caballi in tick cell cultures.     

Nippostrongylus brasiliensis: Peripheral leukocyte responses and correlation of basophils with blood histamine concentration during infection in rats

Rats infected on Day 0 with 3000 infective L₃ larvae of Nippostrongylus brasiliensis, and uninfected controls, were monitored daily through Day 23 postinfection for changes in peripheral leukocytes and blood histamine concentrations. A generalized leukocytosis was observed between Days 7 and 18, the period leading up to and immediately following the time of expulsion of adult worms from the small intestine. The total number of lymphocytes was elevated between Days 11 and 17 post-infection; however, there was no change in the percentage of lymphocytes relative to other white blood cell types. The total number and percentage of monocytes were no different from controls, with the exception of Day 5 postinfection. On that day, there was a significant elevation in the number (614/mm³ blood in infected rats, as compared to 160/mm³ blood in controls) and relative proportion (2.7% of total leukocytes in infected animals, compared to 0.8% in controls) of monocytes, coinciding with the termination of the pulmonary migration of larvae. A period of moderate neutrophilia occurred between Days 7 and 12, but this was not accompanied by any changes in the proportion of neutrophils. A biphasic eosinophil response was observed. An early elevation of eosinophils occurred between Days 3 and 5, corresponding to the period of larval migration through the lungs. A second period of eosinophilia began on Day 11, when worm expulsion was beginning, and continued through Day 19, i.e., beyond the period of worm expulsion. Basophilia was observed as early as Day 6 after infection, rising to a peak on Day 13 (6.8% of total leukocytes in the infected animals, as compared to 0.5% in controls), and declining thereafter, but remaining above control levels until termination of the experiment on Day 23. The histamine content of blood samples, as determined by an enzymic-isotopic assay, closely paralleled the development and decline of basophilia; histamine levels also peaked on Day 13 postinfection (422.5 pg histamine/mm³ blood in infected rats, compared to 66.0 pg histamine/mm³ blood in controls). As basophilia progressed during the course of infection, there was a decline in the amount of histamine per basophil. In uninfected rats and during the first week after infection, basophils contained about 1.5–2.0 pg histamine per cell. In the third week of infection, there was about 0.6 pg histamine per basophil. The time course of the basophilia suggests that these cells may be involved in the expression of immunity to N. brasiliensis.     

Trypanosoma cruzi: effects of anti-thymocyte serum in mice and neonatal thymectomy in rats

CF₁ mice were given eight injections of normal rabbit serum (NRS), Hanks' balanced salt solution (HBSS), or rabbit anti-mouse thymocyte serum (ATS) beginning 3 days prior to and at 3-day intervals subsequent to intraperitoneal (ip) inoculation with 5 × 10⁴ trypomastigotes of a Brazil strain of Trypanosoma cruzi. Markedly enhanced parasitemia, increased numbers of tissue stages (amastigotes), and higher mortality occurred in ATS-treated mice as compared to NRS- or HBSS-treated controls. Administration of three injections of ATS at 3-day intervals during the latter stages of acute Chagas' disease, i.e., when numbers of parasites were declining, resulted in a transitory relapse (increase in numbers) of blood and tissue parasites. No relapse occurred in mice when ATS was administered at 3-day intervals over a period of 15 days during the subacute stage of the disease, i.e., after parasites had disappeared from the blood.Parasitemia and mortality were enhanced in neonatally thymectomized rats when compared to that observed in sham-operated and unoperated control rats following ip injection of 2 × 10⁵ trypomastigotes of T. cruzi. Serum obtained from thymectomized and control rats 5 weeks after inoculation with T. cruzi at a time when the blood of all animals had become microscopically negative for parasites were equally protective in passive transfer experiments, while serum from uninfected controls gave no protection.Gamma globulin levels significantly increased in thymectomized as well as intact rats by the third to fourth week of infection with T. cruzi, reached maximum concentrations in 5–6 wk, and remained elevated significantly at the twelfth week post infection as compared with uninfected controls. No significant changes occurred in total serum proteins or α and β fractions of any group, infected or uninfected.Total circulating leukocytes, especially lymphocytes, were diminished in mice and rats subjected to treatment with ATS or neonatal thymectomy.These data clearly indicate that neonatal thymectomy of rats and ATS treatment of mice suppress the acquired immune response to T. cruzi. Further, passive transfer experiments in rats confirm the protective role of circulating antibody in acquired immunity to Chagas' disease.     

The effect of high altitude on platelet counts, thrombopoietin and erythropoietin levels in young Bolivian airmen visiting the Andes

Recognition of thrombosis as a complication of exposure to high altitude has stimulated interest in rheological changes resulting from hypobaric hypoxia. Previous studies of platelet counts at high altitude have yielded conflicting results and have not been studied in conjunction with potential mediating cytokines. We studied the effects of high-altitude exposure on platelet numbers, thrombopoietin (tpo) and erythropoietin (epo) levels in man. A group of 28 volunteers from the Bolivian Airforce stationed at Santa Cruz (600 m altitude) were studied 48 h and 1 week after their ascent to La Paz (3600 m). In addition 105 volunteers based at Santa Cruz for at least 1 year were compared with 175 age- and sex-matched residents at El Alto (4200 m). Platelet counts were measured immediately after sampling and serum samples assayed for tpo and epo. In the ascending group, mean platelet counts were 251×10⁹, 367×10⁹ and 398×10⁹/l at 600 m and following 48 h and 1 week at 3600 m respectively. Mean tpo levels were 132.5, 76 and 92 pg/ml with epo values of 2.98, 11.6 and 7.9 mIU/ml respectively. In the resident populations mean platelet counts were 271×10⁹/l in the low- and 471×10⁹/l in the high-altitude groups. Mean tpo and epo levels measured 69.3 pg/ml and 4.5 mIU/ml respectively at 600 m and 58.5 pg/ml and 5.1 mIU/ml at 4200 m. In conclusion we have demonstrated a significant and sustained elevation in platelet numbers within 48 h of ascent to high altitude. Our findings do not support a role for tpo as a mediator of the increased platelet count. However, these data do not discount epo as a potential candidate. Received: 28 December 1998 / Revised: 13 May 1999 / Accepted: 26 May 1999     

Babesia argentina: Disseminated intravascular coagulation in acute infections in splenectomized calves

The pathology of severe Babesia argentina infections in splenectomized calves was studied. The calves were infected by intravenous inoculation of 10⁹–10¹⁰B. argentina and given 0.1 mg/kg betamethasone to enhance the parasitemia. Hematological changes observed during detailed studies of the course of infection in eight calves, three of which subsequently died, included thrombocytopenia, leucopenia, and reduced fibrinogen levels. The prothrombin time and partial thromboplastin time were prolonged in all three calves tested, and pathological levels of fibrinogen degradation products were detected in both of two calves tested. Massive pulmonary edema was a constant finding at autopsy of 24 fatal cases. Histopathological examination revealed widespread fibrin thrombi in capillaries and larger vessels of lung, in capillaries of renal glomeruli, and in hepatic sinusoids. The findings established the occurrence of disseminated intravascular coagulation in the acute infections studied.     

Effects of Malaria Parasite Density on Blood Cell Parameters

Changes in blood cell parameters are already a well-known feature of malarial infections. To add to this information, the objective of this study was to investigate the varying effects that different levels of parasite density have on blood cell parameters. Patients diagnosed with malaria at Phobphra Hospital, Tak Province, Thailand between January 1^st 2009 and January 1^st 2012 were recruited as subjects for data collection. Blood cell parameters of 2,024 malaria-infected patients were evaluated and statistically analyzed. Neutrophil and platelet counts were significantly higher, however, RBC count was significantly lower in patients with P. falciparum infection compared to those with P. vivax infection (p<0.0001). Leukocyte counts were also significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia. In terms of differential leukocyte count, neutrophil count was significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia (p<0.0001). On the other hand, both lymphocyte and monocyte counts were significantly lower in patients with high parasitemia (p<0.0001). RBC count and Hb concentration, as well as platelet count were also significantly reduced (p<0.05) and (p<0.0001), respectively. To summarize, patients infected with different malaria parasites exhibited important distinctive hematological parameters, with neutrophil and eosinophil counts being the two hematological parameters most affected. In addition, patients infected with different malarial densities also exhibited important changes in leukocyte count, platelet count and hemoglobin concentration during the infection. These findings offer the opportunity to recognize and diagnose malaria related anemia, help support the treatment thereof, as well as relieve symptoms of severe malaria in endemic regions.     

Diphenyl diselenide modulates nucleotidases,reducing inflammatory responses in the liver of <Emphasis Type="Italic">Toxoplasma gondii</Emphasis>-infected mice

The aim of this study was to verify the effect of diphenyl diselenide (PhSe)₂ on hepatic nucleotidases and on the concentration of purines in mice infected by Toxoplasma gondii. The animals were divided into four groups: Group A (uninfected), Group B (uninfected and treated with (PhSe)₂), Group C (infected), and Group D (infected and treated with (PhSe)₂). The inoculation (groups C and D) was performed with 50 cysts of T. gondii (ME-49 strain). Mice from groups B and D were treated with 5 μmol kg^?1 of (PhSe)₂. Liver tissue from infected mice showed less severe inflammation, elevated ATP/ADO ratio, elevated NTPDase, 5′nucleotidase, and ADA activities compared to the uninfected group (Group A; P < 0.05). However, infected and treated mice showed decreased ATP levels and elevated ADO levels, as well as higher NTPDase and 5′nucleotidase activities and decreased ADA activity in the hepatic tissue compared to the infected group (P < 0.05). Moreover, the (PhSe)₂ treatment of infected mice reduced the hepatic inflammation and showed an immunomodulatory effect on ectonucleotidases of hepatic lymphocytes, which it returned to basal levels. Therefore, chronic infection by T. gondii induces hepatic inflammation in mice, and it is possible that purine levels and nucleotidase activities in hepatic tissue are related to the pathogenesis of the infection in this tissue. The treatment with (PhSe)₂ was able to reverse the hepatic inflammation in mice chronically infected, possibly due to the modulation of purinergic enzymes that produce an anti-inflammatory profile through the purinergic system in the liver tissue.     

The metabolism of sunflower phytoalexins ayapin and scopoletin: plant-fungus interactions

The coumarin phytoalexins ayapin and scopoletin accumulate in longitudinal stem sections of sunflower (Helianthus annuus L., Compositae) following inoculation with fungi both pathogenic (Alternaria helianthi) and nonpathogenic (Helminthosporium carbonum) to this plant. Both compounds were induced more rapidly, and they attained higher levels in tissue inoculated with the heterologous pathogen H. carbonum as compared with the sunflower pathogen A. helianthi. Similarly, scopoletin and ayapin accumulated to comparatively low concentrations following inoculation with a second sunflower pathogen, Phoma macdonaldii. Scopoletin was biosynthesized de novo following inoculation, although levels of its glucoside scopolin exceeded those of the aglucone in both infected and control tissues. Both scopoletin and scopolin were routinely detected in trace amounts in uninoculated tissue. In contrast, ayapin was not detected as a component of uninfected plants. When [¹⁴C]scopoletin was supplied to induced sunflower stem sections about 36% of the recovered radioactivity was in the form of ayapin. In vitro studies demonstrated that A. helianthi possessed the ability to rapidly degrade both scopoletin and ayapin, whereas H. carbonum was much less efficient in these traits. The differential degradation of these compounds by phytopathogenic fungi which do not attack sunflower is also discussed.     

Application of benzothiadiazole and Trichoderma harzianum to control faba bean chocolate spot disease and their effect on some physiological and biochemical traits

Chocolate spot disease is the most prevalent and important disease in the major faba bean growing regions in the world. Different concentrations of the abiotic inducer (0.3 and 0.5 mM benzothiadiazole) and the biotic inducer (1 × 10⁷ and 2 × 10⁷ spore/ml Trichoderma harzianum) were used alone or in combination to study their efficiency against faba bean chocolate spot disease caused by Botrytis fabae and Botrytis cinerea and their effect on some chemical analyses (phenylalanine ammonia lyase activity, total flavonoids and peroxidase isozymes, pectin and lignin content and total chlorophyll content). Application of the tested inducers as foliar treatment significantly reduced the severity of chocolate spot disease as compared with untreated infected plants. The reduction in disease severity was associated with a gradual increase in phenylalanine ammonia lyase activity. Maximum increase was recorded at 72 h after inoculation with B. fabae and B. cinerea. In addition, the levels of flavonoids in induced infected leaves recorded a sharp increase at 24 h after inoculation with B. fabae or B. cinerea. Also, pectin and lignin contents in the cell wall of induced infected plants were significantly increased as compared with untreated infected plants. Beside the induction of resistance, the tested inducers markedly increased total chlorophyll content in treated infected plants as compared with untreated infected plants. Isozymes analysis revealed that new peroxidase bands were induced only in treated faba bean leaves in response to infection with B. fabae or B. cinerea.     

Breakdown in membrane asymmetry regulation leads to monocyte recognition of P. falciparum-infected red blood cells

The human malaria parasite Plasmodium falciparum relies on lipids to survive; this makes its lipid metabolism an attractive drug target. The lipid phosphatidylserine (PS) is usually confined to the inner leaflet of the red blood cell membrane (RBC) bilayer; however, some studies suggest that infection with the intracellular parasite results in the presence of this lipid in the RBC membrane outer leaflet, where it could act as a recognition signal to phagocytes. Here, we used fluorescent lipid analogues and probes to investigate the enzymatic reactions responsible for maintaining asymmetry between membrane leaflets, and found that in parasitised RBCs the maintenance of membrane asymmetry was partly disrupted, and PS was increased in the outer leaflet. We examined the underlying causes for the differences between uninfected and infected RBCs using fluorescent dyes and probes, and found that calcium levels increased in the infected RBC cytoplasm, whereas membrane cholesterol was depleted from the erythrocyte plasma membrane. We explored the resulting effect of PS exposure on enhanced phagocytosis by monocytes, and show that infected RBCs must expend energy to limit phagocyte recognition, and provide experimental evidence that PS exposure contributes to phagocytic recognition of P. falciparum-infected RBCs. Together, these findings underscore the pivotal role for PS exposure on the surface of Plasmodium falciparum-infected erythrocytes for in vivo interactions with the host immune system, and provide a rationale for targeted antimalarial drug design.     

Plasmodium berghei: correlation of in vitro erythrophagocytosis with the dynamics of early-onset anemia and reticulocytosis in mice.

Infection of BALB/c mice with Plasmodium berghei results in an anemia which is excessive to that which can be accounted for solely by direct destruction of infected erythrocytes by the mature schizonts at the time of merozoite release. Mice infected with 10⁴ infected erythrocytes exhibited a progressive anemia beginning on Day 7. Significant reticulocytosis was first observed on Day 9 and parasitemia tended to parallel reticulocytosis with a lag of about 1 day. In studies of erythrophagocytosis, washed erythrocytes from randomly selected mice infected with 10⁵ infected red blood cells were phagocytized by peritoneal macrophages in vitro to a significantly greater extent on Days 3–5 postinfection than were erythrocytes taken from normal controls. The degree of erythrophagocytosis reached a peak on Day 4 and returned to control levels on Days 6 and 7. Erythrocytes taken from infected animals on Day 7 and incubated in normal plasma were phagocytized to a significantly greater extent than were normal erythrocytes incubated in normal plasma or erythrocytes from infected mice incubated in plasma from infected animals. The enhanced in vitro erythrophagocytosis observed on Days 3–5, which preceded and coincided with the beginning of the early-onset anemia on Day 5, may correlate with in vivo phenomena which may contribute to the developing anemia. Furthermore, the restoration of enhanced erythrophagocytosis by normal plasma seems to indicate that some component(s) of normal plasma may be depleted during the early stages of P. berghei infection.     

Trichinella spiralis: skeletal muscle membrane potentials in infected and uninfected mice

Male albino mice were infected orally with 400 ± 10 excysted Trichinella spiralis larvae. Skeletal muscle resting membrane potentials were recorded from the tibialis anterior muscles of infected and uninfected mice on the following days postinfection (PI): 1–15, 18, 20, 24, 28, 30–60 (at 5-day intervals), 90, 120, 150, and 180. The membrane potentials were significantly (P < 0.05) lower in infected muscle (82 vs 85 mV) on Day 30 PI. On Days 60, 90, 120, 150, and 180 PI the mean membrane potential in infected muscle (62 mV) was about 23 mV lower than the mean for uninfected muscle (85 mV) and this difference was highly significant (P < 0.001). These findings are discussed in relationship to other physiological alterations known to occur in skeletal muscles infected with T. spiralis larvae.     

Biomechanical properties of red blood cells infected by Plasmodium berghei ANKA

Malaria is a pathogenic disease in mammal species and typically causes destruction of red blood cells (RBCs). The malaria-infected RBCs undergoes alterations in morphology and its rheological properties, and the altered rheological properties of RBCs have a significant impact on disease pathophysiology. In this study, we investigated detailed topological and biomechanical properties of RBCs infected with malaria Plasmodium berghei ANKA using atomic force microscopy. Mouse (BALB/c) RBCs were obtained on Days 4, 10, and 14 after infection. We found that malaria-infected RBCs changed significantly in shape. The RBCs maintained a biconcave disk shape until Day 4 after infection and then became lopsided on Day 7 after infection. The central region of RBCs began to swell beginning on Day 10 after infection. More schizont stages were present on Days 10 and 14 compared with on Day 4. The malaria-infected RBCs also showed changes in mechanical properties and the cytoskeleton. The stiffness of infected RBCs increased 4.4–4.6-fold and their cytoskeletal F-actin level increased 18.99–67.85% compared with the control cells. The increase in F-actin depending on infection time was in good agreement with the increased stiffness of infected RBCs. Because more schizont stages were found at a late period of infection at Days 10 and 14, the significant changes in biomechanical properties might contribute to the destruction of RBCs, possibly resulting in the release of merozoites into the blood circulation.