First Week Of Infection Research Articles

Differential induction of helper T cell subsets during blood-stage Plasmodium chabaudi AS infection in resistant and susceptible mice.

The induction of T helper cell subsets during the course of non-lethal or lethal blood-stage Plasmodium chabaudi AS infection was investigated using inbred strains of mice which differ in the level of resistance to this intraerythrocytic parasite. Resistant C57Bl/6 mice experience a non-lethal course of infection characterized by moderate levels of both parasitaemia and anaemia and resolution of primary acute infection by 4 weeks, while susceptible A/J mice experience lethal infection with fulminant parasitaemia and severe anaemia. T helper subset function was assessed during infection by determining the kinetics of spleen cell production in vitro of the Th1-derived cytokine, interferon-gamma (IFN-gamma), and of the Th2-derived cytokine, IL-5, using sandwich ELISAs. Spleen cells from resistant C57Bl/6 mice were found to produce high levels of IFN-gamma within 1 week of infection in response to both the mitogen concanavalin A (Con A) and malaria antigen. Furthermore, CD4+ T cells were found to be the source of IFN-gamma while both CD4+ and CD8+ T cells were found to produce IL-5. Decreased IFN-gamma production after day 10 was concomitant with significant production of IL-5 between 2 and 3 weeks post infection. In contrast, spleen cells from susceptible A/J mice produced high levels of IL-5 within the first week of infection. In addition, these animals were found to have high serum levels of IL-5. These results, thus, confirm previous observations that resolution of primary blood-stage P. chabaudi infection occurs by sequential activation of Th1 CD4+ T cells followed by activation of the Th2 subset, and in addition, suggest that induction of a strong Th2 response early in infection may lead to a severe and lethal course of malaria.

Mycobacteria-induced autoantibody production is associated with susceptibility to infection but not with host propensity to develop autoimmune disease.

Mycobacteria cause increase in autoantibody production in the host during the first weeks of infection. The level of the autoantibody enhancement varies widely in different hosts, suggesting that it depends on features of the host make-up. We have investigated the participation of two characteristics of the host in the modulation of mycobacteria-induced autoantibody production: (i) the host being genetically determined to later develop spontaneous autoimmune disease; (ii) the host being susceptible/resistant to mycobacterial infection. Mycobacterium avium infection was studied in 3-month-old mice that are prone (NZB and C57B1/6-lpr/lpr strains) or not (NZW and C.D2 strains) to develop, when older, autoimmune disease; these murine strains are either naturally susceptible (C57B1/6-lpr/lpr and NZW) or resistant (NZB and C.D2) to mycobacteria. Mycobacterium avium infection was produced by i.p. injection of 3 x 10(7) viable bacilli. At days 15 and 30 of the infection, we determined the following parameters: (i) number of cells producing natural autoantibodies (splenic cells showing surface antibodies against bromelain-treated mouse (BrM) erythrocytes); (ii) suppression of the primary response to T cell-dependent antigen (i.e. to sheep erythrocytes); (iii) immunoglobulin classes and IgG isotypes; (iv) titres of anti-dsDNA antibodies; and (v) serum concentrations of interferon-gamma (IFN-gamma). We found that the highest elevations in natural autoantibodies were associated with hosts being naturally susceptible to mycobacteria, but not with the host being genetically determined to later develop autoimmune disease. The rise in autoantibodies was predominantly of the IgM type, being associated with suppression of the T cell response and accompanied by increase in serum IFN-gamma. Mycobacteria failed to induce any significant enhancement in pathogenic anti-dsDNA antibodies. Our data suggest that the finding of a high level of autoantibodies during the early phase of mycobacterial infection reflects host susceptibility of the infectious agent, and that it is not related with its propensity to later develop autoimmune disorders.

O Antigen Protects Bordetella parapertussis from Complement

Bordetella pertussis, a causative agent of whooping cough, expresses BrkA, which confers serum resistance, but the closely related human pathogen that also causes whooping cough, Bordetella parapertussis, does not. Interestingly, B. parapertussis, but not B. pertussis, produces an O antigen, a factor shown in other models to confer serum resistance. Using a murine model of infection, we determined that O antigen contributes to the ability of B. parapertussis to colonize the respiratory tract during the first week of infection, but not thereafter. Interestingly, an O antigen-deficient strain of B. parapertussis was not defective in colonizing mice lacking the complement cascade. O antigen prevented both complement component C3 deposition on the surface and complement-mediated killing of B. parapertussis. In addition, O antigen was required for B. parapertussis to systemically spread in complement-sufficient mice, but not complement-deficient mice. These data indicate that O antigen enables B. parapertussis to efficiently colonize the lower respiratory tract by protecting against complement-mediated control and clearance.

Increased levels of cysteinyl leukotrienes and prostaglandin E2 in gastrointestinal tract mucus are associated with decreased faecal dry matter in Merino rams during nematode infection

Immune-mediated scouring in sheep is a mucosal hypersensitivity response incited by infective larvae of gastrointestinal nematodes in the southern half of Australia and in New Zealand, regions characterised by a Mediterranean, winter-rainfall climate. To gain insights into the underlying mechanism(s), this study investigated the relationship between nematode infection of sheep in pens, faecal dry matter and release of inflammatory mediators in the intestinal tract. Six worm-free, immune rams received a dose of 3000 Trichostrongylus third stage larvae (L3) and 3000 Ostertagia L3 per week for 6 weeks, after which they were euthanased. Three rams acted as uninfected controls. Faecal dry matter was significantly lower in the infected group from the first week of infection until the end of the trial. Concentrations of cysteinyl leukotrienes and prostaglandin E2 were higher in mucus from both the abomasum and the small intestine of infected rams compared with controls. Within the infected group, concentrations of both mediators were higher in mucus from the small intestine than from the abomasum. There were greater numbers of eosinophilic granulocytes and mucosal mast cells in abomasal and small-intestinal tissue sections from infected rams compared with the controls. The results are consistent with the hypothesis that nematode infection causes an inflammatory response in the gastrointestinal mucosa, characterised by increased fluid secretion.

PIR-B-Deficient Mice Are Susceptible to Salmonella Infection.

Paired Immunoglobulin-like receptors of activating (PIR-A) and inhibitory (PIR-B) isoforms are expressed by many blood cell types including B cells, dendritic cells, monocyte/macrophages, granulocytes, mast cells and megakaryocyte/platelets. To determine the role of PIR-B in bacterial infection, PIR-B deficient (PIR-B−/−) and control C57BL/6 mice of the same age and sex were infected intravenously with the attenuated strain of Salmonella typhimurium (WB335). When injected with high doses of bacteria (5 × 104 ∼ 5 × 106 CFU), both types of mice died within 3 to 14 days post infection. When given small doses (103 ∼ 104 CFU), however, PIR-B−/− mice exhibited progressively increasing morbidity beginning at 4-day post-infection over a 4-week period, whereas many control mice could survive (see Figure). PIR-B−/− mice were found to have higher bacterial loads in liver, spleen and lungs than the control mice and bacteremia at days 3 and 7 post-infection. In liver histology typhoid nodules were observed as early as day 1 and their incidence increased during the next six days in both groups of mice. However, quite distinct changes were observed at day 7: in control mice inflammatory cellular lesions were localized and exhibited nodular distribution, whereas in PIR-B−/− mice mononuclear cells infiltrated along the liver sinusoids and exhibited a spreading distribution. There were no significant differences in plasma levels of liver enzymes (ATL, AST and ALK), cytokines (TNFα, IL-10 and IFNγ) and antibodies (IgM, IgG and IgA) against Salmonella between PIR-B−/− and control mice. While splenic lymphoid and myeloid subsets were indistinguishable during the first week of infection, the increases of CD19+ B and CD8+ T cells in infected PIR-B−/− mice were not as marked as those in infected control mice at day 14 post-infection (see Table). For phagocytic cell functions ex vivo, there were no differences in phagocytosis and intracellular killing of bacteria and superoxide anion release between PIR-B−/− and control mice. However, PIR-B−/− macrophages were found to release more nitrite and TNFα upon bacteria stimulation than the control macrophages. These results suggest that PIR-B plays an important regulatory role in bacterial infection.(Supported by NIH/NIAID grants AI42127 and AI52243).Mac-1+ MΦCD4 + TCD8+ TCD19+ BUninfected Control1.3 ± 0.6 *1.4 ± 0.40.7 ± 0.35.1 ± 1.8Uninfected PIR-B−/−1.2 ± 0.31.5 ± 0.21.2 ± 0.24.9 ± 0.3Infected Control19.4 ± 7.05.5 ± 1.52.6 ± 0.710.0 ± 2.6Infected PIR-B−/−16.5 ± 2.34.2 ± 2.11.3 ± 0.64.5 ± 1.3cell numbers (× 107), mean ± 1 S.D. [Display omitted]

Persistent Depots of Influenza Antigen Fail To Induce a Cytotoxic CD8 T Cell Response

Encounter with Ag during chronic infections results in the generation of phenotypically and functionally heterogeneous subsets of Ag-specific CD8 T cells. Influenza, an acute infection, results in the generation of similar CD8 T cell heterogeneity, which may be attributed to long-lived depots of flu Ags that stimulate T cell proliferation well after virus clearance. We hypothesized that the heterogeneity of flu-specific CD8 T cells and maintenance of T cell memory required the recruitment of new CD8 T cells to persistent depots of flu Ag, as was the case for flu-specific CD4 T cell responses. However, robust expansion and generation of highly differentiated cytolytic effectors and memory T cells only occurred when naive CD8 T cells were primed during the first week of flu infection. Priming of new naive CD8 T cells after the first week of infection resulted in low numbers of poorly functional effectors, with little to no cytolytic activity, and a negligible contribution to the memory pool. Therefore, although the presentation of flu Ag during the late stages of infection may provide a mechanism for maintaining an activated population of CD8 T cells in the lung, few latecomer CD8 T cells are recruited into the functional memory T cell pool.

Plasmodium berghei XAT: Contribution of γδ T cells to host defense against infection with blood-stage nonlethal malaria parasite

We examined a potential role of γδ T cells in protective immunity to blood-stage Plasmodium berghei XAT infection. Plasmodium berghei XAT is an attenuated variant of the lethal strain P. berghei NK65 and its infection is self-resolving in immune competent mice. To determine whether γδ T cells are essential for the resolution of P. berghei XAT malaria, mice were depleted of γδ T cells with anti-TCRγδ antibody treatment. Although mice that had received control antibody resolved infections, mice received anti-TCRγδ antibody could not control their infections and eventually died. Spleen cells from infected mice produced IFN-γ and nitric oxide (NO) within the first week of infection, however, levels of IFN-γ and NO in γδ T cell-depleted mice were significantly lower than in control mice. To examine whether γδ T cells are involved in the antibody production, malarial-specific antibodies of the various isotypes were measured in the sera of γδ T cell-depleted mice and control mice. Serum levels of IgG2a, which was known to be a protective antibody in P. berghei XAT malaria, were significantly lower in γδ T cell-depleted mice than in control mice, whereas levels of IgG1 were comparable to those in control mice. Our results indicated that the presence of the γδ T cell subset was essential for resolution of blood-stage P. berghei XAT malaria and played a modulatory role in the development of Th1 response and host defense against this malarial parasites.

The Characterization of Dendritic Cells in the MAIDS Model (43.46)

Abstract Murine acquired immunodeficiency syndrome (MAIDS) is an animal model used to study human AIDS and is induced by murine leukemia virus. There are two different strains of mice used in this model system; BALB/c animals are naturally resistant and C57BL/6 are susceptible to MAIDS. Our laboratory’s previous studies examined differential immune responses during the first week of infection by comparing lymphoid organ gene expression patterns in BALB/c and C57BL/6 mice using DNA microarrays. Based on these data, it appears that the inability of C57/BL6 mice to develop an effective immune response may be due, in part, to changes in dendritic cell function or homing to lymph nodes. Based on microarray results, we hypothesize that this is due to lymphatic vessel remodeling differences. In the first part of this study, strain-specific differences in the mRNA expression patterns of specific DC function related genes identified by DNA microarray (e.g., CD83, DC-SIGN, and DCAR) were quantified using real-time RT-PCR. In the second part of this study, immunofluorescent staining was used to visualize and quantify differences in the lymphatic vessel networks in the lymph nodes of disease resistant versus susceptible mice after MuLV infection. Our data suggest that by 3 days post infection, lymphatic vessel branching is more extensive in BALB/c mice (MAIDS resistant) than C57BL/6 animals (MAIDS susceptible). Further studies are underway to support and further quantify these preliminary results.

Ameboma

61 Hispanic male with a history of hypercholestorolemia was referred to our clinic for a screening colonoscopy. He denied any complaints of weight loss, diarrhea, abdominal pain, hematochezia, melena fever, chills or fatigue. He was originally from South America, but had been in the U.S. for over five years. Our patient had no abnormal labaratory findings. On colonoscopy he was found to have a 2 cm ulcerated, friable flat mass with exudate in the ascending colon just outside the cecum. Histology revealed an ameboma which was described as severe active chronic inflammation with an exudate fragment showing trophozoites with erythrophagocytosis. The patient was treated with 10 days of metronidazole followed by 10 days of paromomycin. Intestinal amebiasis is caused by the protozoan Entamoeba Hystolytica. Worldwide 30–50 million symptomatic infections occur. It is the third most common parasitic cause of death. In the United states most of the cases are seen in immigrants from developing countries and travelers. Infection begins with ingestion of cysts from fecally contaminated water or food. Excystation occurs in the small bowel where trophozoites emerge. Ninety percent of patients colonized by E. Hystolytica spontaneously clear the infection by one year. Most patients are asymptomatic, however invasive intestinal amebiasis may mimic inflammatory bowel disease, malignancy and malsbsorptive illnesses. Extraintestinal manifestations are uncommon. They include liver abscesses, pleuropulmonary disease, cerebritis and pericarditis. Diagnosis is made by serologic and stool examinations.Microscopic examination of the stool has a low sensitivity 30–60%. A high false positive rate exists secondary to non pathogenic entamoebas which are morphologically identical to and more common then entamoeba hystolytica.ELISA stool antigen test which detects adherence lectin antigen has a sensitivity of 87% and a specificity of greater than than 90%. Seum antibody tests are most useful for extraintestinal disease when organisms are not found in the stool. Antibodies are detectable by the first week of infection and may persist for years. Up to 25% of uninfected patients in endemic regions are positive. An Ameboma is an unususual manifestation of entamoeba hystolytica. In immigrants from developing countries with atypical colonic masses one must consider entamoeba hystolytica as part of their differential diagnosis.

Schistosoma mansoni: A diagnostic approach to detect acute schistosomiasis infection in a murine model by PCR

Schistosomiasis represents an increasing problem in non-endemic areas, due to the growing number of immigrants and to tourists contracting this disease in “off-the-beaten-track” tourism. Acute schistosomiasis is not diagnosed early due to the lack of diagnostic tools that are sufficiently sensitive enough to detect the parasite during the first weeks of infection. We have developed a diagnostic approach based on the detection of parasite DNA by polymerase chain reaction (PCR) in urine, comparing the performance of this new approach with the two currently used schistosomiasis diagnostic tools (Kato-Katz and ELISA) and the PCR in stool samples. This comparison was done in a Schistosoma mansoni murine experimental model, which permits follow up of the parasite from the acute to the chronic stage of infection. Our results suggest that this new PCR-based approach could be useful for the detection of acute schistosomiasis in easy-to-handle clinical samples such the urine.

Pertussis toxin inhibits neutrophil recruitment to delay antibody-mediated clearance of Bordetella pertussis

Whooping cough is considered a childhood disease, although there is growing evidence that children are infected by adult carriers. Additionally, increasing numbers of vaccinated adults are being diagnosed with Bordetella pertussis disease. Thus it is critical to understand how B. pertussis remains endemic even in highly vaccinated or immune populations. Here we used the mouse model to examine the nature of sterilizing immunity to B. pertussis. Antibodies were necessary to control infection but did not rapidly clear B. pertussis from the lungs. However, antibodies affected B. pertussis after a delay of at least a week by a mechanism that involved neutrophils and Fc receptors, suggesting that neutrophils phagocytose and clear antibody-opsonized bacteria via Fc receptors. B. pertussis blocked migration of neutrophils and inhibited their recruitment to the lungs during the first week of infection by a pertussis toxin-dependent (PTx-dependent) mechanism; a PTx mutant of B. pertussis induced rapid neutrophil recruitment and was rapidly cleared from the lungs by adoptively transferred antibodies. Depletion of neutrophils abrogated the defects of the PTx mutant. Together these results indicate that PTx inhibits neutrophil recruitment, which consequently allows B. pertussis to avoid rapid antibody-mediated clearance and therefore successfully infect immune hosts.

Mycobacterium tuberculosiscontrols host innate immune activation through cyclopropane modification of a glycolipid effector molecule

Mycobacterium tuberculosis (Mtb) infection remains a global health crisis. Recent genetic evidence implicates specific cell envelope lipids in Mtb pathogenesis, but it is unclear whether these cell envelope compounds affect pathogenesis through a structural role in the cell wall or as pathogenesis effectors that interact directly with host cells. Here we show that cyclopropane modification of the Mtb cell envelope glycolipid trehalose dimycolate (TDM) is critical for Mtb growth during the first week of infection in mice. In addition, TDM modification by the cyclopropane synthase pcaA was both necessary and sufficient for proinflammatory activation of macrophages during early infection. Purified TDM isolated from a cyclopropane-deficient pcaA mutant was hypoinflammatory for macrophages and induced less severe granulomatous inflammation in mice, demonstrating that the fine structure of this glycolipid was critical to its proinflammatory activity. These results established the fine structure of lipids contained in the Mtb cell envelope as direct effectors of pathogenesis and identified temporal control of host immune activation through cyclopropane modification of TDM as a critical pathogenic strategy of Mtb.

Cytokine and antibody production during the course of resolution in Plasmodium yoelii 17XL-infected BALB/c mice treated with febrifugine and isofebrifugine mixture from leaves of Hydrangea macrophylla var. Otaksa.

Cytokine and antibody production was investigated during the course of resolution of primary infection in Plasmodium yoelii 17XL-infected BALB/c mice treated with a mixture of febrifugine and isofebrifugine. The infected mice in an untreated control group showed a progressively increasing parasitemia, leading to mouse death. In contrast, infected mice given the mixture orally showed low parasitemia levels during administration. Following a transient increase in parasitemia in the bloodstream of the treated mice, no parasites could be detected by microscopic examination. Analysis of cytokines in plasma showed that the plasma IFN-gamma levels elevated significantly within the first week of infection in both groups. Furthermore, on day 20 the plasma IFN-gamma and IL-4 levels elevated significantly in the treated mice and the production of both cytokines was sustained until at least day 40. The production of both cytokines in the treated mice was coincident with a decrease in parasitemia. The production of parasite-specific antibodies in the course of P. yoelii 17XL infection was also monitored. In the drug-treated mice, the titers of parasite-specific IgG1, IgG2a, IgG2b and IgG3 elevated significantly from day 20; and the production of parasite-specific antibodies was coincident with a decrease in parasite numbers in the bloodstream.

Tracking the killers: how should we measure CD8 T cells in HIV infection?

Most immunologists agree that CD8 T cells are important in controlling viruses, at least after the first week of infection – the time it takes for naive CD8 T cells to expand and differentiate into antiviral cytotoxic T lymphocytes (CTL). Nonetheless, CD8 T-cell measurements in HIV clinical studies show little relation to disease prognosis. There are two possible interpretations – either CD8 T cells are not important in established HIV infection or we are not measuring the right things.

Respiratory syncytial virus induces pneumonia, cytokine response, airway obstruction, and chronic inflammatory infiltrates associated with long-term airway hyperresponsiveness in mice.

Respiratory syncytial virus (RSV) infection is associated with acute morbidity (e.g., pneumonia and airway obstruction [AO]) and long-term complications (e.g., airway hyperresponsiveness [AHR]). We present a comprehensive evaluation of the acute and chronic phases of RSV respiratory tract infection, using a mouse model. BALB/c mice were inoculated with RSV and monitored for 154 days. RSV loads and cytokines were measured in bronchoalveolar lavage (BAL) samples. Pneumonia severity was assessed using a standard histopathologic score, and pulmonary function was determined by plethysmography. RSV-infected mice exhibited viral replication that peaked on day 4-5 and became undetectable by day 7. These mice developed acute pneumonia (peak days, 4-5) and chronic pulmonary inflammatory infiltrates that lasted up to 154 days after inoculation. BAL concentrations of tumor necrosis factor- alpha, interleukin (IL)-6, interferon- gamma, IL-4, IL-10, KC (an IL-8 homologue), MIG (CXCL9), RANTES, macrophage inflammatory protein-1 alpha, and eotaxin were significantly higher in RSV-infected mice than in control mice. RSV-infected mice developed acute AO during the first week of infection that persisted for 42 days. RSV-infected mice also showed significant AHR in response to methacholine up to 154 days. This model provides a means to investigate the immunopathogenesis of RSV infection and its association with reactive airway disease.

Infrapopulation dynamics of a wild strain of Taenia crassiceps (WFU) (Cestoda: Taeniidae) in BALB/cJ mice.

Taenia crassiceps cysticerci form large infrapopulations that persist in the tissues of their rodent hosts. Early infrapopulation growth appears inhibited and is followed by rapid increases that appear not to be controlled by the host immune response. This investigation was undertaken to examine the infrapopulation growth dynamics of a normally developing strain (WFU) of T. crassiceps during a 60-day primary intraperitoneal (i.p.) infection. Three, 6, 9, 14, 28, and 60 days after i.p. inoculation of 5 cysticerci, mice were killed, and the numbers of larvae, developmental stage, and buds per larva were recorded. Larval infrapopulation abundance increased exponentially beginning on day 6 postinoculation (PI), indicating an initial lag in reproduction. A stage-structured exponential growth model, assuming no mortality, fits the larval infrapopulation dynamics in terms of the numbers of larvae in reproductive and nonreproductive stages, indicating that cysticerci evade or suppress (or both) host immune mechanisms that are parasite restrictive after the first week of infection.

CTLA-4 blockade inhibits induction of Helicobacter pylori-associated gastritis in mice.

The balance between Th1 and Th2 response determines the outcome of Helicobacter pylori infection. Interferon (IFN)-gamma plays an inductive role in gastric inflammation, whereas interleukin (IL)-4 counterbalances Th1 response and suppresses the development of gastritis. Th cell response is regulated by co-stimulatory factors. A co-stimulatory molecule, cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), plays an inhibitory role in IL-2-dependent cell growth and mediates an optimal inhibitory signal to Th1 and Th2 cells. We administered anti-CTLA-4 monoclonal antibody (MoAb), which blocks CTLA-4 signalling, to examine the relative role for this signalling during maturation of Th1 and Th2 cells in H. pylori infection in mice. Mice treated by anti-CTLA-4 MoAb within the first week of infection showed an inhibition of gastric inflammation, accompanied by an increasing ratio of H. pylori-specific IgG1/IgG2a in serum following infection. Furthermore, the treatment resulted in the higher ratio of IL-4/IFN-gamma by splenocytes in response to H. pylori antigen at 6 weeks after infection, compared with untreated mice. These results suggest that the predominance of Th2 response by CTLA-4 blockade leads to an inhibition of the development of gastric inflammation. CTLA-4 signalling could contribute to the regulation of Th subsets and the development of gastric inflammation in H. pylori infection.

Administration of anti-CD3 monoclonal antibody during experimental Chagas' disease induces CD8+ cell-dependent lethal shock.

The injection of the 145-2C11 anti-CD3 MoAb in mice induces a polyclonal T cell activation resulting in the release of several cytokines, including interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). As these cytokines are known to be involved in the host defence against Trypanosoma cruzi, we measured serum levels of IFN-gamma and TNF-alpha after injection of the 145-2C11 MoAb in the course of experimental murine Chagas' disease. Compared with control mice, T. cruzi-infected BALB/c mice were found to be primed to secrete very high levels of IFN-gamma and TNF-alpha from the second and the first week of infection, respectively, up to the chronic phase. In vivo cell depletion experiments indicated that CD8+ T cells were responsible for these dramatic hyperproductions of IFN-gamma and TNF-alpha. While all control mice survived anti-CD3 MoAb injection, a high lethality rate was observed in T. cruzi-infected mice within 24 h after anti-CD3 MoAb challenge. Pretreatment with neutralizing anti-IFN-gamma MoAb or depletion of CD8+ T cell population dramatically decreased the mortality induced by anti-CD3 MoAb in T. cruzi-infected mice. Finally, we showed that anti-CD3 MoAb injection in T. cruzi-infected mice was followed by a massive release of nitric oxide (NO) metabolites, which was partially reduced by IFN-gamma or TNF-alpha neutralization. The administration of the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) before anti-CD3 MoAb challenge did not prevent and even enhanced lethality in T. cruzi-infected mice, suggesting that NO overproduction and lethal shock are not causally related. We conclude that injection of anti-CD3 MoAb in the course of experimental Chagas' disease induces a CD8+ cell-dependent shock mediated by IFN-gamma and TNF-alpha.

Fasciola hepatica: the effect of food quality on the development of redial generations in Galba truncatula infected with allopatric miracidia.

Individual bimiracidial infections of French Galba truncatula with an allopatric (Moroccan) isolate of Fasciola hepatica were carried out under laboratory conditions to count free rediae and intraredial daughter rediae in snails just after their death, and to determine whether feeding the snails on lettuce only or lettuce plus Tetraphyll had an effect on the development of redial generations. Controls consisted of snails infected with sympatric (French) miracidia and reared with lettuce only. In the allopatric group, reared with lettuce only as food, a higher mortality rate of snails in the first 4 weeks of the experiment was noted, and most G. truncatula showed 1-sporocyst infections, with the usual development of redial generations. Compared to the sympatric group, the growth of the first mother redia (R1a redia) in each snail of the allopatric group was significantly slower during the first weeks of infection, whereas a significantly increased formation of intraredial daughter rediae in the other mother rediae (R1b rediae) was noted over the same period. In the allopatric group, reared with cos lettuce and commercial fish food, 1-sporocyst infections (45.5% of snails) and 2-sporocyst infections (53.9%), with the usual development of redial generations, were noted. Compared to the sympatric group, a significantly slower development of the first mother redia during the first weeks of the experiment was noted in the 1-sporocyst infections, whereas the values in the 2-sporocyst infections did not significantly differ from those noted in the sympatric group. Similar results were noted for the production of intraredial daughter rediae in the R1b rediae during the first weeks of the experiment. In all infections derived from the growth of a single sporocyst per snail, the differentiation of numerous daughter rediae inside R1b rediae would be induced by the slow growth of the R1a redia (from which the most important group of R2a rediae originated) during the first weeks of infection and might represent a mechanism to replace free rediae absent from the inside of the snail.

Polarization of cytokine responses in B- and T-lymphocytes during Staphylococcus aureus infection

The destructive course of Staphylococcus aureus arthritis is due to certain leukocytes and their products, mainly cytokines. The cellular source of cytokines mediating this inflammatory process has not been previously assessed on a protein level. Using a mouse model of hematogenously induced S. aureus infection the intracellular production of IFN-γ, IL-4 and IL-10 in splenic B and T cells have been determined. This has enabled us to define distinct Th1 vs Th2 and Be1 vs Be2 populations of lymphocytes participating in S. aureus infection. Spleen cells were obtained before, and at different time intervals during the first week of infection and re-stimulated in vitro with staphylococcal peptidoglycan, formalin killed staphylococci and TSST-1. The different antigens used for re-stimulation gave rise to different cytokine profiles in analysed T cells (identified as CD4+) and B cells (identified as CD19+). TSST-1 acted as the most potent re-stimulator and we found that 40% of the CD4+ cells responded with IFN-γ production, and unexpectedly almost 20% of the CD19+ cells. As to IL-4 and IL-10 production, the percentage of B cells expressing these cytokines was higher than the percentage T cells and the peak of their appearance appeared later than that of IFN-γ. This finding indicates that Be1 cells are an important source of IFN-γ early during the infection and that the production of the Th2 cytokines in B cells downregulates its production of IFN-γ. In conclusion this study shows that both B and T cells contribute to the cytokine production during S. aureus infection in a complex pattern.