Antibody response and avidity of respiratory syncytial virus-specific total IgG, IgG1, and IgG3 in young children

Respiratory syncytial virus (RSV) is a major cause of acute respiratory disease in infants and young children. Considering that several aspects of the humoral immune response to RSV infection remain unclear, this study aimed to investigate the occurrence, levels, and avidity of total IgG, IgG1, and IgG3 antibodies against RSV in serum samples from children ≤5 years old. In addition, a possible association between antibody avidity and severity of illness was examined. The occurrence and levels of RSV-specific IgG depended on age, with infants <3 months old displaying high levels of antibodies, which were probably acquired from the mother. Children ≥24 months old also showed frequent occurrence and high levels of IgG, which was produced actively during infection. In addition, the avidity assay showed that the avidity of RSV-specific total IgG and IgG1 was lower in infants <3 months old who had acute respiratory disease than in age-matched controls. The avidity of RSV-specific IgG detected in children ≥24 months old with lower respiratory infection was lower than that in children with upper respiratory infection. These results indicate that the presence of high avidity RSV-specific IgG antibodies may lead to better protection against RSV infection in children <3 months old, who may have a lower probability of developing disease of increased severity. In addition, children ≥24 months old with RSV-specific IgG antibodies of low avidity tended to develop more severe RSV illness. These findings may be helpful in establishing vaccination schedules when a vaccine becomes available.

Azithromycin and spiramycin induce anti-inflammatory response in human trophoblastic (BeWo) cells infected by Toxoplasma gondii but are able to control infection

Toxoplasma gondii is an important pathogen which may cause fetal infection if primary infection. Our previous studies have used human choriocarcinoma trophoblastic cells (BeWo cell line) as experimental model of T. gondii infection involving placental microenvironment. This study aimed to examine the effects of azithromycin and spiramycin against T. gondii infection in BeWo cells. Cells were treated with different concentrations of the macrolide antibiotics and analyzed first for cell viability using thiazolyl blue tetrazole (MTT) assay. As cell viability was significantly decreased with drug concentrations higher than 400 μg/mL, the concentration range used in further experiments was from 50 to 400 μg/mL. The number of infected cells and intracellular replication of T. gondii decreased after treatment with each drug. The infection induced up-regulation of the macrophage migration inhibitory factor (MIF), which was also enhanced in infected cells after treatment with azithromycin, but not with spiramycin. Analysis of the cytokine profile showed increase TNF-α, IL-10 and IL-4 production, but decreased IFN-γ levels, were detected in infected cells and treated with each drug. In conclusion, treatment of human trophoblastic BeWo cells with with azithromycin or spiramycin is able to control the infection and replication of T. gondii. In addition, treatment with these macrolides, especially with azityromycin induces an anti-inflammatory response and high MIF production, which can be important for the establishment and maintenance of a viable pregnancy during T. gondii infection.

Evaluation of vertical transmission of Toxoplasma gondii in Calomys callosus model after reinfection with heterologous and virulent strain

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes a variety of clinical syndromes, but the infection is severe in immunocompromised individuals and during pregnancy due to the possibility of transplacental transmission of the parasite causing congenital toxoplasmosis. Vertical transmission of the parasite usually occurs when females are primarily infected during pregnancy. Calomys callosus is resistant to T. gondii ME49 strain, which presents a moderate virulence and congenital disease occurs only during the acute phase of infection. The aim of this study was to determine whether vertical transmission occurs when females of C. callosus chronically infected with ME49 strain of T. gondii are reinfected with a highly virulent strain (RH, type I). Females were infected with cysts of the ME49 strain. On the 1st day of pregnancy, animals were reinfected with tachyzoites of the RH strain. In the 19th day of pregnancy, placentas and embryos were processed for morphological analysis, immunohistochemistry and for detection of the parasite by PCR and mouse bioassay. Morphological and immunohistochemical analyses revealed the presence of parasites only in placental tissues. Mouse bioassay results showed seroconversion only in mice that were inoculated with placental tissues. Also, T. gondii DNA was detected only in placental samples. Congenital toxoplasmosis does not occur in C. callosus females chronically infected with the moderately virulent ME49 strain of T. gondii and reinfected with the highly virulent RH strain, thus indicating that primary T. gondii infection before pregnancy leads to an effective long-term immunity preventing transplacental transmission to the fetus.

Evaluation of Toxoplasma gondii and Neospora caninum infections in sheep from Uberlândia, Minas Gerais State, Brazil, by different serological methods

Toxoplasmosis and neosporosis have been recognized as economically important diseases with considerable impact on the livestock industry. Considering the scarce information on the occurrence of Toxoplasma gondii and Neospora caninum infections in sheep from Uberlândia, Minas Gerais State, Brazil, this study aimed to investigate the frequency of antibodies against these parasites in sheep sera from this region by using different serological methods. A total of 155 sheep serum samples were analyzed by the indirect fluorescence antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) for the detection of IgG against T. gondii and N. caninum. Seroreactivity by IFAT showed 80% of samples with titers between 512 and 2048 for T. gondii (cutoff ≥ 64) and 78% presenting titers between 50 and 200 for N. caninum (cutoff ≥ 50). Seroreactivity by ELISA showed 75% of samples with ELISA index (EI) between 2.0 and 3.0 for T. gondii (cutoff ≥ 1.3) and 54% presenting EI between 1.3 and 2.0 for N. caninum (cut off ≥ 1.3). Discordant results by both tests were analyzed by immunoblot, resulting in a total seropositivity of 61% for T. gondii and 23% for N. caninum, with 41% to T. gondii only, 3% to N. caninum only, and 20% to both parasites. There was a significant positive association between seropositivity to T. gondii and age over one year (P<0.001), but such association was not found for N. caninum infection. In conclusion, as T. gondii and N. caninum infections are simultaneously present in sheep flocks of this region, it should be emphasized the importance to carry out a regular monitoring of Toxoplasma infection due to its high prevalence, its zoonotic potential and induction of reproductive disorders leading to economic losses. For neosporosis, sheep farmers should be instructed about the presence of the parasite in the flock, its risk factors and potential abortifacient role in sheep. Differential flock management could be valuable tool to establish the association of serological positivity and reproductive disease induced by N. caninum in sheep.

Differential susceptibility of human trophoblastic (BeWo) and uterine cervical (HeLa) cells to Neospora caninum infection

Neospora caninum is an apicomplexan parasite, closely related to Toxoplasma gondii, and causes abortion and congenital neosporosis in cattle worldwide. Trophoblast cells act in mechanisms of innate immune defense at the fetal-maternal interface and no data are available about the interaction of Neospora with human trophoblasts. Thus, this study aimed to verify the susceptibility of human trophoblastic (BeWo) compared with uterine cervical (HeLa) cell lines to N. caninum. BeWo and HeLa cells were infected with different parasite:cell ratios of N. caninum tachyzoites and analyzed at different times after infection for cell viability using thiazolyl blue tetrazole and lactate dehydrogenase assays. Both cell lines were also evaluated for cytokine production and parasite infection/replication assays when pre-treated or not with Neospora lysate antigen (NLA) or human recombinant IFN-γ. Cell viability was increased up to 48 h of infection in both types of cells, suggesting that infection could inhibit early cell death and/or induce cell proliferation. Neospora infection induced up-regulation of the macrophage migration inhibitory factor (MIF), mainly in HeLa cells, which was enhanced by cell pre-treatment by NLA or IFN-γ. Conversely, parasite infection induced down-regulation of the transforming growth factor (TGF-β), mostly in BeWo cells, which was decreased with NLA or IFN-γ pre-treatment. HeLa cells were more susceptible to Neospora infection than BeWo cells and IFN-γ pre-treatment resulted in reduced infection indices in both cell lines. Control of parasite growth was mediated by IFN-γ through an indoleamine-2,3-dioxygenase-dependent mechanism in HeLa cells alone. Based on these results, we concluded that BeWo and HeLa cells are readily infected by N. caninum, although presenting differences in susceptibility to infection, cytokine production and cell viability. Thus, these host cells can be considered in comparative approaches to understand strategies used by N. caninum to survive at the maternal-fetal interface.

Galectin-3 plays a modulatory role in the life span and activation of murine neutrophils during early Toxoplasma gondii infection

Galectins are beta-galactoside-binding lectins involved in several biological processes and galectin-3 (Gal-3) is related to modulation of immune and inflammatory responses. This study aimed to evaluate the role of Gal-3 in the life span and biological functions of murine neutrophils during in vitro infection by virulent Toxoplasma gondii RH strain. Inflammatory peritoneal neutrophils (Nphi) from C57BL/6 wild-type (WT) and Gal-3 knockout (KO) mice were cultured in the presence or absence of parasites and analyzed for phosphatidylserine (PS) exposure and cell death using Annexin-V and propidium iodide staining, and cell viability by MTT assay. Cell toxicities determined by lactate dehydrogenase (LDH), degranulation by lysozyme release, and cytokine production were measured in Nphi culture supernatants. Phorbol myristate acetate (PMA)- or zymosan-dependent reactive oxygen species (ROS) were measured in Nphi cultures. Our results demonstrated that Gal-3 is involved in the increase of the viable Nphi number and the decrease of PS exposure and cell death following T. gondii infection. We also observed that Gal-3 downmodulates T. gondii-induced Nphi toxicity as well as Nphi degranulation regardless of infection. Furthermore, Gal-3 expression by Nphi was associated with increased levels of IL-10 in the beginning and decreased levels of TNF-alpha later on, regardless of parasite infection, as well as with decreased levels of IL-6 and increased IL-12 levels, following early parasite infection. Our results also showed that Gal-3 suppresses PMA- but not zymosan-induced ROS generation in Nphi following T. gondii infection. In conclusion, Gal-3 plays an important modulatory role by interfering in Nphi life span and activation during early T. gondii infection.

Apoptosis and S phase of the cell cycle in BeWo trophoblastic and HeLa cells are differentially modulated by Toxoplasma gondii strain types

Transplacental transmission of Toxoplasma gondii causes congenital toxoplasmosis, one of the most severe forms of infection. The ability of the parasite to survive intracellularly largely depends on the blocking of different proapoptotic signaling cascades of the host cells. During pregnancy, however, alterations in the incidence of apoptosis are associated with abnormal placental morphology and function. The aim of this study was to evaluate the incidence of apoptosis and cell proliferation in trophoblastic (BeWo cell line) and uterine cervical (HeLa cell line) cells infected with a highly virulent RH strain or a moderately virulent ME49 strain of T. gondii. BeWo and HeLa cells were infected with RH or ME49 tachyzoites (2:1 and 5:1; parasite:cell) or medium alone (control). After 2 h, 6 h and 12 h of incubation, cells were fixed in 10% formalin and analyzed by immunohistochemistry to determine the apoptosis (expression of cytokeratin 18 neo-epitope--clone M30) and cell in S phase (expression of proliferating cell nuclear antigen--PCNA) indices. RH strain-infected BeWo and HeLa cells showed a lower apoptosis index than non-infected controls, whereas a higher apoptosis index was found in ME49 strain-infected cells compared to controls. In addition, RH-infected cells displayed lower apoptosis index than ME49-infected cells, even though active caspase-3 was detected in both cell types infected with either RH or ME49 strains as well in non-infected cells in all analyzed times of infection. Also, the cell S phase indices were higher in ME49 strain-infected BeWo and HeLa cells as compared to non-infected controls and RH strain-infected cells. These results indicate that RH and ME49 strains of T. gondii possess opposing mechanism of interference in apoptosis and cell cycle S phase of both BeWo and HeLa cells and these differences can be associated to evasion strategies of the parasite to survive inside the host cells.

CpG-ODN combined with Neospora caninum lysate, but not with excreted-secreted antigen, enhances protection against infection in mice

CpG oligodeoxynucleotides (ODN) have shown to be potent immunoadjuvants for several pathogens, but there is limited information concerning their use in immunization protocols against neosporosis. This study aimed to evaluate the potential of CpG-ODN combined with Neospora lysate antigen (NLA) or excreted-secreted antigen (NcESA) to induce protective immune response against Neospora caninum infection in mice. C57BL/6 mice were vaccinated subcutaneously three times at 2-week intervals with NLA, NLA+CpG, NcESA, NcESA+CpG, CpG (adjuvant control) or PBS (infection control). Serological assays showed an increased specific IgG2a response in animals immunized with either antigen plus adjuvant and elevated levels of the IgG1 isotype in those vaccinated with antigens alone. Splenocyte proliferative responses upon antigen stimulation were higher in groups immunized with NLA or NcESA combined with CpG, showing increased IL-12 levels. Also, mice vaccinated with NcESA or NcESA+CpG demonstrated higher IFN-gamma levels and IFN-gamma/IL-10 ratio. After lethal challenge, mice immunized with NLA+CpG or NLA had lower morbidity score and body weight changes in comparison to other groups, and animals did not succumb during acute infection. In contrast, NcESA+CpG or NcESA groups exhibited the highest morbidity scores, body weight impairment and mortality rates, associated with greatest brain parasite burden and inflammation. In conclusion, CpG-ODN was able to induce a Th1-type humoral immune response with predominant IgG2a levels for either NLA or NcESA, but resulting in an effective Th1-driven cellular immune response and total protection only when combined with NLA. Vaccination with NcESA alone or combined with CpG resulted in a strong cellular immune response associated with high levels of IFN-gamma and inflammation, rendering mice more susceptible to parasite challenge.

BeWo trophoblast cell susceptibility to Toxoplasma gondii is increased by interferon-gamma, interleukin-10 and transforming growth factor-beta1

The present study aimed to investigate BeWo trophoblast cell susceptibility to Toxoplasma gondii infection under stimulation with anti-inflammatory cytokines in comparison with HeLa cells. Both cell types were submitted to different treatments with recombinant cytokines [interleukin (IL)-10 and transforming growth factor (TGF)-beta1] or the respective antibodies (anti-IL-10 and anti-TGF-beta) before and after T. gondii infection. The effect of interferon (IFN)-gamma was also assessed alone or in combination with anti-inflammatory cytokines or the respective antibodies after the parasite infection. Cells were fixed, stained and parasites quantified under light microscopy to evaluate intracellular replication (mean number of parasites per cell in 100 infected cells) and infection index (percentage of infected cells per 100 examined cells). In contrast with HeLa cells, treatments with IL-10 or TGF-beta1 induced a considerable augmentation in both T. gondii intracellular replication and invasion into BeWo cells. In addition, treatment with IFN-gamma alone or associated with IL-10 or TGF-beta1 increased the same parameters in BeWo cells, whereas the opposite effect was observed in HeLa cells. When endogenous IL-10 or TGF-beta was blocked, both BeWo and HeLa cells were able to control the parasite infection only in the presence of IFN-gamma. Together, these results indicate that the higher susceptibility of BeWo cells to T. gondii may be due to immunomodulation mechanisms, suggesting that the role of trophoblast cells in maintaining a placental microenvironment favourable to pregnancy may facilitate the infection into the placental tissues.

Evaluation of serological tests for the diagnosis of Neospora caninum infection in dogs: Optimization of cut off titers and inhibition studies of cross-reactivity with Toxoplasma gondii

Diagnosis of Neospora caninum infection in dogs is based on serological assays such as the indirect fluorescent antibody test (IFAT) and enzyme-linked immunosorbent assays (ELISA). This study evaluated two serological tests (IFAT and ELISA) for the detection of IgG antibodies to N. caninum in 300 serum samples of dogs through the optimization of cut off titers by using the two-graph receiver-operating characteristic (TG-ROC) curve. In addition, the identification of major cross-reactive antigens with Toxoplasma gondii was investigated by inhibition ELISA and immunoblotting (IB) assays. IFAT and ELISA results showed 74% agreement, with a good negative concordance (P(neg)=0.83), but a poor positive concordance (P(pos)=0.42). The great majority (86%) of sera with positive concordant results (IFAT+/ELISA+) recognized at least two out of three N. caninum immunodominant antigens, particularly the 29-32 and 35-37 kDa bands. Optimization of cut off titers in IFAT and ELISA was performed considering the reactivity to at least two out of three N. caninum immunodominant antigens as infection markers, obtaining a titer of 50 for IFAT and 200 for ELISA. Seropositivity to N. caninum was significantly associated with T. gondii-seropositive samples, particularly in ELISA (55.4%). Inhibition ELISA curves for N. caninum showed a partial heterologous inhibition, indicating some degree of cross-reactivity between N. caninum and T. gondii antigens. Inhibition IB assays showed a moderate heterologous inhibition for N. caninum antigens above 45-50 kDa. These results indicate that ELISA should be used critically when crude tachyzoite antigen preparations are employed, due to possible cross-reactivity with other related parasites as T. gondii. Also, the cut off dilution of 1:50 in IFAT showed to be the most appropriated for N. caninum serology in dogs. Therefore, we suggest that N. caninum immunodominant antigens, specially the 17 and 29-32 kDa proteins, should be selected markers in serological assays for canine neosporosis.

Histological and serological evidence of experimental paracoccidioidomycosis in Calomys callosus (Rodentia: Cricetidae)

The responses of animal experimental models related to the infectivity, virulence and pathogenicity of Paracoccidioides brasiliensis is constantly used to develop new perspectives of investigation. The rodent Calomys callosus, Rengger 1830 (Rodentia: Cricetidae) is an indigenous inhabitant of the savannah environment found in the central regions of Brazil. The aim of the present work was to evaluate the histopathological and serological features of C. callosus after inoculation with the Pb18 strain of P. brasiliensis. Furthermore, A/Sn and B10.A mice strains were also tested to compare the results obtained in C. callosus to these well-established experimental models of resistance and susceptibility respectively. In every instance, survival analysis was performed, and histopathological study of the lungs, liver and spleen was employed to investigate tissue involvement, degree of inflammation and fungal presence. Levels of antibodies to P. brasiliensis were measured by using an enzyme-linked immunosorbent assay after 4 weeks and at the advanced stage of infection. The mortality rate was proportional to inoculation dose in all groups, but overall it was much superior in C. callosus than in the B10.A-susceptible mice. Macroscopical and microscopical pathological alterations were also more extensive and remarkable for C. callosus, once again proportional to inoculation dose, but more noticeable differences among the studied groups were found with 0.6x10(5) inoculum. In addition, the serological profile of C. callosus was similar to that found for B10.A-susceptible mice. Infection of C. callosus with 0.6x10(8) Pb18 inoculum resulted in more serious illness, and it decreased in severity in proportion to the inoculum dose. This difference was more pronounced in C. callosus, and the clinical, serological and pathological findings in this animal were more intense and precocious compared with the B10.A-susceptible mice. The present results suggest that C. callosus is a potentially alternative experimental animal model for paracoccidioidomycosis infection.

Susceptibility to vertical transmission of Toxoplasma gondii is temporally dependent on the preconceptional infection in Calomys callosus

Toxoplasma gondii is an obligate intracellular parasite that causes a variety of clinical syndromes, but the infection is more severe in immunocompromised individuals and in cases of congenital toxoplasmosis. This study aimed to verify if the susceptibility to vertical transmission of Toxoplasma gondii is temporally dependent on the preconceptional infection in Calomys callosus. Twelve C. callosus females were infected with 20 cysts of T. gondii ME49 strain and divided into three groups of four animals that were mated after approximately 10 days (group 1), 30 days (group 2), and 50 days (group 3) of infection. The animals were sacrificed from the 17th to 20th day of pregnancy, when placentas and embryos were collected for morphological and immunohistochemical studies, mouse bioassay for evaluating seroconversion and PCR for detecting parasite DNA. Serum samples from C. callosus females and mice used in bioassay were analysed for the detection of IgG antibodies to T. gondii by ELISA. Detection of T. gondii was observed by mouse bioassay and PCR in placentas and embryos from C. callosus females infected around 10 days pre-conception. However, only placentas, but not embryos, from females infected around 30 and 50 days pre-conception showed positivity for parasite DNA and seroconversion by mouse bioassay. In conclusion, this study model shows that vertical transmission of T. gondii may take place when maternal infection occurs within one month before conception, thus demonstrating the time of preconceptional seroconversion that rule out a risk of congenital toxoplasmosis.

The binding of CCL2 to the surface of Trypanosoma cruzi induces chemo-attraction and morphogenesis

Adhesion of Trypanosoma cruzi to host cells employs mechanisms which are complex and not completely understood. Upon infection, host cells release pro-inflammatory cytokines and chemokines in the environment. These had been found to be involved with increasing parasite uptake as well as killing by macrophages and cardiomyocytes. In the present study, we focused on the interaction of murine beta-chemokine CCL2 with trypomastigote forms of T. cruzi. We found that this chemokine directly triggers the chemotaxis and morphogenesis of trypomastigote forms of parasites. Binding assays showed that the interaction of CCL2 with molecules present in trypomastigote forms is abolished by the addition of condroitin 6-sulphate, a glycosaminoglycan. Moreover, we also observed that the parasite glycoproteins are the major players in this interaction. In summary, our study demonstrates a host ligand/parasite receptor interaction that may have relevant implications in the tissue tropism of this important parasitic disease.

BeWo Trophoblasts are Unable to Control Replication of Toxoplasma gondii, Even in the Presence of Exogenous IFN-γ

The ability of RH strain of Toxoplasma gondii to invade and grow into BeWo cells was investigated in the present study using IFN-gamma, l-tryptophan, or alpha-methyl-tryptophan treatments. HeLa cells were used in the same conditions for comparison purposes. It was demonstrated that BeWo cells are more permissive to T. gondii infection, making them more susceptible to this pathogen when compared to HeLa cells. Infection rates of BeWo cells do not show any significant alteration in different protocols using IFN-gamma. In addition, BeWo treated with l-tryptophan was unable to significantly increase parasite growth. In contrast, HeLa cells treated with IFN-gamma or IFN-gamma plus l-tryptophan are able to impair or increase, respectively, parasite replication, providing evidence that this indoleamine-2,3-dioxygenase-dependent phenomenon is operant in these cells, whereas it is inactive in BeWo. Therefore, our data support the hypothesis that the immunological mechanisms controlling infection at the maternal-fetal interface are different from those occurring in the periphery. At the same time that operating regulatory mechanisms work inside and outside the cells located at that microenvironment to prevent maternal rejection of the concept, these events might facilitate the progression of infection caused by intracellular pathogens, as T. gondii.

Detection of immunoglobulin G antibodies to Neospora caninum in humans: high seropositivity rates in patients who are infected by human immunodeficiency virus or have neurological disorders

Considering that little is known about the epidemiology of Neospora caninum infection in humans, particularly in populations with high Toxoplasma gondii infection rates, the present study aimed to investigate the presence of antibodies to N. caninum in T. gondii-seropositive and -seronegative individuals. A total of 256 serum samples divided into four groups (61 samples from human immunodeficiency virus [HIV]-positive patients, 50 samples from patients with neurological disorders, 91 samples from newborns, and 54 samples from healthy subjects) were assessed for N. caninum and T. gondii serologies by indirect fluorescent-antibody test, enzyme-linked immunosorbent assay, and immunoblotting (IB). Immunoglobulin G antibodies to N. caninum were predominantly detected in HIV-infected patients (38%) and patients with neurological disorders (18%), while newborns and healthy subjects showed lower seropositivity rates (5% and 6%, respectively). Seropositivity to N. caninum was significantly associated with seropositivity to T. gondii in both HIV-infected patients and patients with neurological disorders. Seroreactivity to N. caninum was confirmed by IB, with positive sera predominantly recognizing the 29-kDa antigen of N. caninum. The results of this study indicate the presence of N. caninum infection or exposure in humans, particularly in HIV-infected patients or patients with neurological disorders, who could have opportunistic and concurrent infections with T. gondii. These findings may bring a new concern for the unstable clinical health of HIV-infected patients and the actual role of N. caninum infection in immunocompromised patients.

Evaluation of homologous, heterologous, and affinity conjugates for the serodiagnosis of Toxoplasma gondii and Neospora caninum in maned wolves (Chrysocyon brachyurus)

Use of serological tests in the diagnosis of infectious diseases in wild animals has several limitations, primarily the difficulty of obtaining species-specific reagents. Wild canids, such as maned wolves (Chrysocyon brachyurus), are highly predisposed to infection by Toxoplasma gondii and, to a lesser extent, to Neospora caninum. The aim of the present study was to evaluate homologous, heterologous, and affinity conjugates in enzyme-linked immunosorbent assays (ELISAs) and indirect fluorescent antibody tests (IFATs) for detecting immunoglobulin (Ig) G antibodies against T. gondii and N. caninum in maned wolves. Serum samples were obtained from 59 captive animals in Brazil and tested by ELISA for T. gondii serology and IFAT for N. caninum serology using 3 different enzymatic and fluorescent conjugates: homologous (guinea pig anti-maned wolf IgG-peroxidase and -fluorescein isothiocyanate [FITC]), heterologous (rabbit anti-dog IgG-peroxidase and -FITC), and affinity (protein A-peroxidase and -FITC). Seropositivity to T. gondii was comparable among the homologous (69.5%), heterologous (74.6%), and affinity (71.2%) enzymatic conjugates. A significant positive correlation was found between the antibody levels determined by the 3 enzymatic conjugates. The highest mean antibody levels (ELISA index = 4.5) were observed with the protein A-peroxidase conjugate. The same seropositivity to N. caninum (8.5%) was found with the homologous and heterologous fluorescent conjugates, but protein A-FITC was not able to detect or confirm any positive samples with homologous or heterologous conjugates. Our results demonstrate that homologous, heterologous, and affinity conjugates might be used in ELISA for serological assays of T. gondii in wild canids, whereas for N. caninum infection, only the homologous or heterologous fluorescent conjugates have been shown to be useful.

Immunization with MIC1 and MIC4 induces protective immunity against Toxoplasma gondii

Host cell invasion by Toxoplasma gondii is tightly coupled to the apical release of micronemal proteins (MIC). In this work, we evaluated the protective effect encountered in C57BL/6 mice immunized with MIC1 and MIC4 purified from soluble tachyzoite antigens by affinity to immobilized lactose. The immunized mice presented high serum levels of IgG1 and IgG2b specific antibodies. MIC1/4-stimulated spleen cells from immunized mice produced IL-2, IL-12, IFN-gamma, IL-10, but not IL-4, suggesting the induction of a polarized Th1 type immune response. When orally challenged with 40 cysts of the ME49 strain, the immunized mice had 68% fewer brain cysts than the control mice. Immunization was associated with 80% survival of the mice challenged with 80 cysts, contrasting with 100% mortality of the non-immunized mice in the acute phase. In this phase, there was much lower parasitism in the lungs and small intestine of the immunized mice, and they did not exhibit the early-stage signs of intestinal necrosis, which was clearly detected in the control mice. Our data demonstrate that MIC1 and MIC4 triggered a protective response against toxoplasmosis, and that these antigens are targets for the further development of a vaccine.

Down-modulation of nitric oxide production in murine macrophages treated with crude plant extracts from the Brazilian Cerrado

Several plant species from the Cerrado biome in Brazil are popularly used as herbal medicines for its reputed analgesic, anti-acid, anti-microbial, anti-inflammatory and anti-tumoral properties, among others. It has been reported that some plant extracts interfere in the production of nitric oxide (NO), an important inflammatory mediator. In the present study, we investigated the effect of hexanic and ethanolic extracts from three plant species on NO production by LPS/IFN-gamma-activated J774 macrophages based on traditional use. The cytotoxic effect of the crude extracts was determined by the thiazolyl blue test (MTT) to measure cell viability. Serjania lethalis stem extracts and Cupania vernalis leaf extracts significantly inhibited NO production, while extracts from Casearia sylvestris var. lingua were inactive or showed low activity on NO production, or were very cytotoxic. The ethanolic stem bark and leaf extracts of Serjania lethalis and Cupania vernalis, respectively, almost completely inhibited the production of NO by J774 macrophages. It can be concluded that the selected extracts are potential sources of active compounds that might be used as anti-inflammatory agents.

Attachment and invasion of host cells by Toxoplasma gondii

Recent studies indicate that Toxoplasma gondii attachment is mediated via a parasite ligand-host cell receptor interaction. Lloyd Kosper and Jose Mineo here survey factors involved in the attachment to and penetration and invasion of host cells by T. gondii.

Seroprevalence of Toxoplasma gondii and Neospora caninum in captive maned wolves (Chrysocyon brachyurus) from southeastern and midwestern regions of Brazil

The main purpose of the present study was to investigate the occurrence of antibodies against T. gondii and N. caninum in captive maned wolves from Brazil, considering that little information is available at the literature about infections by these parasites in this wild animal. Serum samples were obtained from 59 maned wolves originated from six zoos and from one ecological reserve of the southeastern and midwestern regions of Brazil. To detect IgG antibodies against T. gondii, an ELISA protocol was used and the results were expressed as ELISA reactivity indexes (EI). Serology for N. caninum was carried out by indirect fluorescent antibody test (IFAT) and cut-off titers were established at 1:25 dilution. From the total of the analyzed samples, 44 (74.6%) were seropositive for T. gondii and only 5 (8.5%) for N. caninum. Seropositivity for T. gondii ranged from 0 to 100% in the seven different origin locals, with rates over 50% among the six zoos, whereas no positivity was found in the samples from ecological reserve. For N. caninum, seroprevalence varied from 0 to 50% in the different locals, with the highest rates also detected in zoos. Seroprevalence for T. gondii was strongly related with age, with rates significantly higher among adult wolves (91.7%) when compared to newborn or young animals. Seropositive samples for N. caninum were found predominantly in adult wolves. For both parasites, seroprevalence did not show a significant distinction in relation to gender. Although seroprevalence for T. gondii was significantly higher when compared to N. caninum in the Brazilian captive maned wolves tested, these findings reflect the great exposure of this species to T. gondii and, in lower extension, to N. caninum. Also, the present study demonstrated for the first time the presence of antibodies to N. caninum in wild life from South America.

A comparison between IgG antibodies against Eimeria acervulina, E. maxima, and E. tenella and oocyst shedding in broiler-breeders vaccinated with live anticoccidial vaccines

The aim of this study was to compare the IgG response against Eimeria acervulina, E. maxima, and E. tenella and oocyst shedding in broiler-breeders vaccinated with live (virulent or attenuated) anticoccidial vaccines. Serum and faeces samples were collected from chickens before (4 days of age) and after (25 days of age) vaccination with virulent (group A) or attenuated (group B) vaccines and unvaccinated control birds (group C). Criteria for evaluation included the number of oocysts shed on the litter (McMaster technique), the levels of specific serum IgG (ELISA) and the frequencies of antigenic fractions recognised by IgG antibodies (immunoblotting). The results demonstrated that the virulent vaccine (A) presented an ideal association (low oocyst number and high IgG positive rate) for E. acervulina and E. tenella while the immunised flock with the attenuated vaccine (B) demonstrated this ideal association only for E. maxima. Both vaccinated flocks demonstrated a better association for three Eimeria spp. studied when compared to the control group, which presented a divergent association (high oocyst number and low IgG positive rate), particularly for E. acervulina. Immunoblotting assays revealed different antigenic fractions that may be considered as immunodominant antigens. The present study suggests that E. acervulina is critically present in the region studied and the use of live anticoccidial vaccines (virulent or attenuated) showed to be effective to control the clinical coccidiosis in vaccinated flocks.

Effect of Toxoplasma gondii infection kinetics on trophoblast cell population in Calomys callosus, a model of congenital toxoplasmosis

This work evaluated the kinetics of events that occur in the placenta of Calomys callosus after Toxoplasma gondii infection. Animals on the first day of pregnancy (dop) and virgin nonpregnant females were perorally infected with 20 cysts of T. gondii strain ME49. After 100 days of infection, the virgin animals were mated and received an additional 20 cysts on the first dop. The placentas and the embryos from both acutely and chronically infected animals were analyzed up to day 20 of pregnancy by morphological and immunocytochemical assays. Noninfected and infected animals exhibited placenta with normal morphology. From the seventh dop and infection onwards, liver and spleen cells of the infected animals contained several parasitophorous vacuoles. On the 13th day, the maternal blood present at the placental blood spaces contained T. gondii-infected leukocytes. Infected placental cells were only seen on the 15th dop, being the trophoblast giant cells, the first cell type to contain signs of the parasite internalization, followed by labyrinth zone cells 24 h later and spongiotrophoblast cells only after the 19th dop. Fetal liver and brain were infected by T. gondii concomitantly to the labyrinth cell infection. No signals of infection were observed on placentas and embryos from chronically infected animals. Therefore, considering the sequence of events leading to the infection of the various organs, it could be hypothesized that the placenta is infected later on during pregnancy, which may be related to the defense roles played by this structure. However, trophoblast giant cells are unable to completely stop the progression of T. gondii infection towards the fetal tissues. C. callosus was demonstrated to be a suitable experimental model to study the dynamics of congenital toxoplasmosis.

Immune response to respiratory syncytial virus in young Brazilian children

We have evaluated the cellular and humoral immune response to primary respiratory syncytial virus (RSV) infection in young infants. Serum specimens from 65 patients <=12 months of age (39 males and 26 females, 28 cases <3 months and 37 cases > or = 3 months; median 3 3.9 months) were tested for anti-RSV IgG and IgG subclass antibodies by EIA. Flow cytometry was used to characterize cell surface markers expressed on peripheral blood mononuclear cells (PBMC) from 29 RSV-infected children. There was a low rate of seroconversion in children <3 months of age, whose acute-phase PBMC were mostly T lymphocytes (63.0 +/- 9.0%). In contrast, a higher rate of seroconversion was observed in children >3 months of age, with predominance of B lymphocytes (71.0 +/- 17.7%). Stimulation of PBMC with RSV (2 x 10(5) TCID50) for 48 h did not induce a detectable increase in intracellular cytokines and only a few showed a detectable increase in RSV-specific secreted cytokines. These data suggest that age is an important factor affecting the infants' ability to develop an immune response to RSV.

Heterologous antibodies to evaluate the kinetics of the humoral immune response in dogs experimentally infected with Toxoplasma gondii RH strain

An IgM capture ELISA using heterologous antibodies was developed to evaluate the kinetics of the humoral immune response in dogs experimentally infected with Toxoplasma gondii RH strain. Detection of parasite in tissues from inoculated dogs was evaluated by mouse bioassay and immunohistochemical techniques. Serum samples were obtained at regular intervals up to 62 days post-inoculation (p.i.), when the animals were necropsied and their tissues examined. Antibody levels were measured by IgM capture ELISA (McELISA), indirect hemagglutination (IHA), indirect fluorescent antibody test (IgG-IFAT) and indirect immunoenzymatic assay (IgG-ELISA). All dogs seroconverted but only one exhibited severe clinical signs of infection. IgM antibodies were detected by McELISA from the seventh day on, with decreasing IgM levels around the 27th day. Similar results were obtained from IHA, although McELISA showed earlier and longer detection of IgM antibodies. IgG antibodies were detected from the seventh day on, and throughout the period of observation. Immunohistochemical findings and mouse bioassay revealed the presence of free tachyzoites in tissues of the clinically affected dog only. These results suggest that T. gondii acute infection in dogs shows a remarkably transient IgM synthesis, and this feature may constitute an important marker of active infection. Furthermore, McELISA was shown to be a potential tool to diagnose canine toxoplasmosis.

Mast cells in the eyes of Calomys callosus(Rodentia: Cricetidae) infected by Toxoplasma gondii

The mast cell is a powerful effector cell for the innate immune system, acting through the secretion of several distinct mediators. Few studies have demonstrated the relationship between mast cells and toxoplasmosis. In this study, mast cells were investigated in two experimental Toxoplasma infections using Calomys callosus (Rodentia: Cricetidae) as the host. Animals were inoculated either intraperitoneally or via the conjunctiva with tachyzoites of Toxoplasma gondii (RH strain) and sacrificed after 5 days or 24 h, respectively. Enucleated eyes were processed for histological and ultrastructural analysis. Neither experimental infection altered the localization of mast cells compared to control eyes, but they did lead to an accumulation in some tissues as well as to their activation. There was a significant increase in the number of mast cells within 5 days and 24 h after infection. The ocular lesions were characterized by the presence of tachyzoites, inflammatory cells and vasodilatation in the iris and retina. In conclusion, mast cells were mobilized in these experimental infections, suggesting that they play an important role in the host inflammatory response after infection with T. gondii.