Limited role for CD4+ T-cell help in the initial priming of Trypanosoma cruzi-specific CD8+ T cells

Immune control of the protozoan parasite Trypanosoma cruzi requires the activation of both CD4+ and CD8+ T cells. We recently identified two T. cruzi trans-sialidase peptides that are targets of approximately 30% of all CD8+ T cells during acute T. cruzi infection in mice. To determine whether CD4+ T cells are required for generation of these dominant CD8+ T-cell responses, major histocompatibility complex class II (MHC II)-deficient mice were infected with the Brazil strain of T. cruzi and examined for the generation of antigen-specific CD8+ T cells. Strong trans-sialidase TSKB18- and TSKB20-specific CD8+ T-cell responses were generated in both the presence and the absence of CD4+ help. However, the magnitudes of the immunodominant TSKB20-specific CD8+ T-cell responses detectable using class I MHC-peptide tetramers were consistently lower in the blood and spleens of MHC II-deficient mice. Spleen cells from infected MHC II-deficient mice produced gamma interferon after in vitro stimulation with T. cruzi peptides at levels similar to those in wild-type mice, and MHC II-deficient mice displayed strong T. cruzi peptide-specific cytotoxic T-lymphocyte activity in vivo. Thus, primary CD8+ T-cell responses in experimental T. cruzi infection are generated in the absence of CD4+ T cells, providing further evidence that T. cruzi directly activates and licenses antigen-presenting cells. Nevertheless, unhelped CD8+ T cells in T. cruzi-infected mice fail to reach the frequencies achieved in the presence of CD4 T-cell help and are unable to prevent acute-phase death of these mice.     

Changes in T-Lymphocyte Subsets in Lungs and Spleens of Mice with Slowly Progressive Primary Mycobacterium tuberculosis Infection: Involvement of Unconventional T-Cell Subsets

Our previous study showed that the cell-activation responses and cytokine-secretion patterns were different in lungs and spleens of mice with slowly progressive primary Mycobacterium tuberculosis infection. The aim of the present study was to characterize the T-cell subsets in lungs and spleens of mice with a similar infection. The percentages of T-cell subsets were determined by flow cytometry and the absolute numbers were calculated. Spleens of infected mice showed a threefold expansion of CD4+ cells but no change in CD8+ cells, whereas lungs had a threefold increase of both subsets. A significant expansion of CD4-CD8-alphabeta+ [double negative (DN)alphabeta+] subsets was observed in the lungs of infected mice compared with uninfected mice. This was not the case in the spleens of infected mice. In infected mice the CD4-CD8- (DN) population preferentially expressed alphabeta-T-cell receptors (TCR) in the lungs but gammadelta-TCR in the spleens. The percentages of many T-cell subsets were significantly higher in the lungs than in the spleens of both uninfected and infected mice. However, the percentages of CD4+ and CD4-CD8+TCR- subsets in the lungs were significantly lower than in the spleens of infected mice. We also observed some previously unreported T-cell subsets: double positive-TCR- (DPTCR-), DPalphabeta+ and DPgammadelta+. So far their functions are unknown.     

Protective immunity in murine histoplasmosis: functional comparison of adoptively transferred T-cell clones and splenic T cells.

In this study, I examined whether a murine T-cell line and three clones that recognize Histoplasma capsulatum antigens in vitro could confer protection in vivo against a challenge of Histoplasma yeasts. C57BL/6 mice were each inoculated with 5 X 10(4) yeasts intravenously; 1 h later, 5 X 10(6) or 2 X 10(7) resting T cells were inoculated intravenously. At week 1 of infection, the T-cell line and all clones failed to reduce the number of H. capsulatum CFU in the spleens of mice compared with numbers in infected controls. Administration of recombinant interleukin 2 or cyclophosphamide to infected mice did not potentiate the functional activity in vivo of either the T-cell line or the clones. In contrast, inoculation with 2 X 10(7) CD4+ but not CD8+ cells isolated from the spleens of mice immunized with 10(6) viable yeast cells sharply diminished the number of CFU in the spleens of infected animals. Moreover, splenic CD4+ cells from immune mice transferred a delayed-type hypersensitivity response, whereas the T-cell line and clones did not. Injection Injection of an equal number of cloned T cells and CD8+ splenocytes from immune mice did not transfer resistance to infected mice. Additional studies were undertaken to determine if the ineffectiveness of cloned T cells was associated with a failure to migrate to and survive within spleens of infected mice. B6.PL Thy-1a/Cy mice, which are genetically identical to C57BL/6 mice except that T cells of the former bear Thy-1.1 rather than Thy-1.2, were inoculated with Histoplasma yeasts and then injected with immune CD4+ splenocytes or a T-cell clone. At days 1 and 7 of infection, virtually no Thy-1.2+ cells were detected in the spleens of infected mice given cloned T cells. However, the spleens of animals inoculated with immune CD4+ cells contained a small but significant (P less than 0.01) proportion of Thy-1.2+ cells at both day 1 and day 7 postinoculation of H. capsulatum. Thus, the failure of T-cell clones to transfer protection against H. capsulatum may be explained by defective trafficking or poor survival in vivo or both.     

The behavior and pathogenicity ofToxacara canis larvae in mice of different strains

In the present study the behavior and pathogenicity of second-stage larvae ofToxocara canis were examined in different mouse strains with special emphasis on the major histocompatibility complex (MHC). Mice of the inbred strains BALB, C3H, C57BL, and DBA and the outbred strain NMRI were infected orally with 1000 second-stage larvae ofT. canis. The clinical behavior of the animals: the numbers of larvae detected in the liver, lungs, brain and musculature; the hematological and serological parameters; and histological sections were examined. In mice of the BALB strain, no death occurred during the entire period of the investigation and the pattern of body-weight development of infected and uninfected animals was almost identical. The highest larval counts in the brain of all strains were found in BALB mice. The percentage of eosinophils in the blood of BALB mice increased after the 8th week postinfection, whereas it decreased in the other strains. Histological and pathophysiological changes developed to a lesser extent in this strain than in the other strains. In mice of the strains C3H, C57BL, DBA, and NMRI, deaths occurred from the 4th week postinfection onward. The infected animals lost weight in comparison with the uninfected controls; the numbers of larvae found in the brains of infected mice of the above-mentioned strains were lower than those detected in the BALB strain. There is no evidence that mechanical damage caused by migrating larvae in the brain tissue is mainly responsible for symptoms of central nervous toxocariasis. Likewise, the assumption that the MHC is involved in the allergicinflammatory response in the brain could not be proven: infected mice of the BALB and DBA strains reacted completely differently, although both are equipped with the same MHC haplotype.     

Evolution of inflammatory response and cellular immune responses in a murine model of disseminated blastomycosis.

A reproducible model of disseminated blastomycosis was established in C57BL/6 mice by intravenous injection of 10(6) yeast-phase Blastomyces dermatiditis organisms. The infection progressed over 5 weeks to involve lungs, brains, superficial fascia, livers, and spleens of mice. By week 5, there was a greater number of organisms in lungs and brains than in livers and spleens. The tissue response in lungs, brains, and livers progressed from acute neutrophilic invasion before week 1 to pyogranuloma formation by week 5. Lymph nodes and spleens were remarkably spared. By week 5, infected mice became anergic to intradermal challenge with both specific Blastomyces antigen and a nonspecific antigen (sheep erythrocytes). At this time, the response to concanavalin A or phytohemagglutinin by splenocytes was markedly less than that of normal controls. Likewise, the plaque-forming cell response to sheep erythrocytes by splenocytes from infected mice was diminished. In coculture studies, splenocytes from 5-week-infected mice reduced the plaque-forming cell response by normal splenocytes. The development of this murine model should prove useful for elucidating the perturbations of immunoregulation associated with disseminated blastomycosis.     

Phenotypic Characterization of Splenic T Cells from Mice Infected with Plasmodium chabaudi chabaudi

T cells from spleens of mice infected with the erythrocytic stages of Plasmodium chabaudi chabaudi have been analysed with respect to their expression of surface molecules CD3, CD4 and CDS and T-cell receptor (TCR)αβ and γδ. The majority of T cells from infected mice were αβTCR ⁺. However, there was an increase of approximately 8–10-fold in the proportion and total number of γδ T cells. Immunocytochemical analysis of sections of spleens taken from infected C57BL/6 mice during a primary infection showed that this increase took place particularly in the non-lymphoid areas. Within the αβ TCR⁺ T-cell population, both CD4⁺ T cells and CD8⁺ T cells were represented in proportions similar to those observed in normal uninfected mice. Stimulation of splenic T cells from infected mice with P. chabaudi-infected erythrocytes in vitro resulted ina blasted cell population composed predominantly of αβTTCR⁺ T cells with no preferential expansion of γβTCR⁺ T cells. There was no evidence of superantigen-like stimulation of T cells bearing particular Vβ chains of the TCR. The representation of the different Vβ chains within the population was not significantly different from that seen in uninfected mice.     

<Emphasis Type="Italic">Toxocara canis</Emphasis> larvae reinfecting BALB/c mice exhibit accelerated speed of migration to the host CNS

Using a small animal imaging system, migratory activity of Toxocara canis larvae stained by carboxyfluorescein succinimidyl ester (CFSE) was observed post primary infection (PPI) and post reinfection (PR) of BALB/c mice. Each infection was performed with 1,000 larvae per mouse. Primary infections were performed with labeled larvae, while for challenge infections the reinfecting larvae were stained by CFSE. The worm burden in mouse organs was determined during a period from 6 h to 21 days and 4 months PPI and PR. In comparison with primary infections that led to the first larvae appearance in the brain after 60 h, greatly accelerated migration of the parasites administered 3 weeks PPI to the CNS and eyes of challenged mice was noted—in both organs the larvae appeared 6 h PR. In all challenged mice, reinfecting larvae prevailed in the resident parasite population. Preliminary experiments with Toxocara cati larvae also revealed early brain involvement in primarily infected mice. Staining of T. canis larvae by CFSE had no effect on the development of a humoral antibody response against T. canis excretory–secretory antigens. In ELISA, elevated levels of specific IgG and IgG1 were noted on day 14 PPI and the levels of antibodies increased till the end of experiment. Reinfection induced an increase in the levels of both antibodies. In terms of optical density, IgG1 antibodies gave higher values in all sera examined. In ELISA for IgG antibodies, an increase in the avidity index of around 50% was detected 1 month PPI; higher-avidity antibodies were also detected in sera of reinfected animals.     

Bartonella henselae-Specific Cell-Mediated Immune Responses Display a Predominantly Th1 Phenotype in Experimentally Infected C57BL/6 Mice

Immune responses of the immunocompetent host to Bartonella henselae infection were investigated in the murine infection model using C57BL/6 mice. Following intraperitoneal infection with human-derived B. henselae strain Berlin-1, viable bacteria could be recovered from livers and spleens during the first week postinfection, while Bartonella DNA remained detectable by PCR in the liver for up to 12 weeks after infection. Granulomatous lesions developed in livers of infected mice, reached maximal density at 12 weeks after infection, and persisted for up to 20 weeks, indicating that B. henselae induced a chronic granulomatous hepatitis in the immunocompetent murine host. T-cell-mediated immune responses were analyzed in vitro by means of spleen cell proliferation and cytokine release assays as well as analysis of immunoglobulin G (IgG) isotypes. Spleen cells from infected mice proliferated specifically upon stimulation with heat-killed Bartonella antigen. Proliferative responses were mainly mediated by CD4+ T cells, increased during the course of infection, peaked at 8 weeks postinfection, and decreased thereafter. Gamma interferon, but not interleukin-4, was produced in vitro by spleen cells from infected animals upon stimulation with Bartonella antigens. Bartonella-specific IgG was detectable in serum of infected mice by 2 weeks, and the antibody concentration peaked at 12 weeks postinfection. IgG2b was the prominent isotype among the Bartonella-specific serum IgG antibodies. These data indicate that B. henselae induces cell-mediated immune responses with a Th1 phenotype in immunocompetent C57BL/6 mice.     

Myeloid‐derived suppressor cells are key players in the resolution of inflammation during a model of acute infection

Myeloid‐derived suppressor cells (MDSCs) are key players in the immune suppressive network. During acute infection with the causative agent of Chagas disease, Trypanosoma cruzi, BALB/c mice show less inflammation and better survival than C57BL/6 (B6) mice. In this comparative study, we found a higher number of MDSCs in the spleens and livers of infected BALB/c mice compared with infected B6 mice. An analysis of the two major MDSCs subsets revealed a greater number of granulocytic cells in the spleens and livers of BALB/c mice when compared with that in B6 mice. Moreover, splenic MDSCs purified from infected BALB/c mice inhibited ConA‐induced splenocyte proliferation. Mechanistic studies demonstrated that ROS and nitric oxide were involved in the suppressive activity of MDSCs, with a higher number of infected CD8⁺ T cells suffering surface‐nitration compared to uninfected controls. An upregulation of NADPH oxidase p47 phox subunit and p‐STAT3 occurred in MDSCs and infected IL‐6 KO mice showed less recruitment of MDSCs and impaired survival. Remarkably, in vivo depletion of MDSCs led to increased production of IL‐6, IFN‐γ, and a Th17 response with very high parasitemia and mortality. These findings demonstrate a new facet of MDSCs as crucial regulators of inflammation during T. cruzi infection.     

Type 1 and type 2 cytokine-producing mouse CD4+ and CD8+ T cells in acute Schistosoma mansoni infection

CD4⁺ and CD8⁺ T cells can be divided based on the cytokines that they secrete into type 1 (Th1, Tc1) and type 2 (Th2, Tc2) subsets. Schistosoma mansoni infection in mice is characterized by a type 2-dominated response. We have used intracellular cytokine staining to demonstrate dramatic changes in the relative numbers of Tc1 and Th2 cells in the spleens of mice during acute schistosome infection. In infected mice prior to egg laying a generalized type 1 response dominated, and was associated with an expansion in the frequency of Tc1 and Th1 cells. By week 7 after infection the cytokine response was of type 2, with an increase in the numbers of Th2 cells and a dramatic reduction in the frequency of Tc1 cells. Following the onset of egg laying there was apoptosis of cells in the spleens of mice, with CD4⁺ and in particular CD8⁺ T cells undergoing apoptosis. The loss of CD8⁺ T cells may in part be attributable to the development of a type 2 environment, following egg laying, with type 2 responses mediating the apoptosis of Tc1 cells. Schistosome regulation of Tc1 during egg laying may be required to prevent type 1 inflammatory responses from exacerbating egg-induced pathology.     

Immune response to Mycobacterium bovis bacille Calmette Guérin infection in major histocompatibility complex class I- and II-deficient knock-out mice: contribution of CD4 and CD8 T cells to acquired resistance

Knock-out mice with defined major histocompatibility complex (MHC) deficiencies were infected intravenously with Mycobacterium bovis bacille Calmette Guérin (M. bovis BCG) to assess the relative impact of MHC class I- and II-dependent immune responses. Heterozygous control mice were capable of controlling growth of M. bovis BCG, although infection progressed chronically, as assessed by determination of colony-forming units. Furthermore, infected controls developed granulomatous lesions at the site of mycobacterial growth and delayed-type hypersensitivity (DTH) reactions after challenge with purified protein derivative of tuberculin. In vitro, spleen cells from heterozygous control mice produced high concentrations of interferon-γ (IFN-γ) after restimulation with mycobacterial antigens. In contrast, the MHC class II-deficient Aβ^?/? mice, which are virtually devoid of functional CD4 T cells, succumbed to M. bovis BCG infection. Furthermore, Aβ^?/? mice lacked DTH reactions to tuberculin and only few minute picnotic lesions were formed in livers of infected mice. Finally, spleen cells from infected Aβ^?/? mice failed to produce measurable IFN-γ concentrations after restimulation in vitro with various mycobacterial antigen preparations. The capacity of β2-microglobulin (β2m)-deficient mice, which are devoid of CD8α/β T cells, to inhibit growth of M. bovis BCG was only slightly affected at low inocula, although significantly higher colony-forming units were detected in spleens. These knock-out mice developed strong DTH responses to tuberculin and their spleen cells produced high levels of IFN-γ once reactivated by mycobacterial antigens. Furthermore, in livers of infected β2m-deficient mice, extravascular infiltrates developed which were more diffuse than those in infected control littermates. Remarkably, the β2m-deficient mice were substantially more susceptible to higher inocula of M. bovis BCG than their control littermates. Our data formally prove the essential role of MHC class II-dependent immune mechanisms in all relevant aspects of immunity to M. bovis BCG. In addition, our findings emphasize an important contribution of MHC class I-dependent immunity to effective anti-mycobacterial protection. We assume that CD4 T cells are highly effective in containing M. bovis BCG within distinct granulomatous lesions, but fail to eradicate their intracellular pathogens. It appears most likely that CD8 T cells are also required to achieve this goal.     

Experimental toxocariasis and hyperactivity in mice

An observational study using videorecordings and computerassisted data analysis was undertaken in order to investigate the behaviour of mice infected with larvae ofToxocara canis. The findings indicated that the infection had a marked effect on five readily and reliably differentiable categories of murine behaviour. A marked increase in the number of shorter bouts of each of the five behaviours was also associated with the infection. These results support previous findings and further suggest thatT. canis infection affects the way in which mice respond to their environment. In particular the infection appears to be associated with hyperactivity in mice. Possible causes of such behavioural abnormalities as well as implications of these findings for clinical studies concerned with relationships betweenT. canis infection and hyperactivity in children are discussed.     

Generation and maintenance of Listeria-specific CD8+ T cell responses in perforin-deficient mice chronically infected with LCMV

Disruption of the perforin gene results in primary immunodeficiency and an increased susceptibility to opportunistic pathogens. Perforin-deficient (PKO) mice fail to clear primary lymphocytic choriomeningitis virus (LCMV) Armstrong, resulting in persistent infection and functional exhaustion of virus-specific CD8+ T cells. CD8+ T cell responses to Listeria monocytogenes (LM) challenge within the first week after LCMV infection were diminished in both WT and PKO mice, and correlated with enhanced bacterial clearance. However, bacterial challenge at later time points generated similar CD8 T cell responses in both groups of mice. The phenotype and function of pre-existing LM-specific memory CD8+ T cells were maintained in persistently infected PKO mice. Thus persistent LCMV infection, as a result of perforin deficiency, results in dysfunction of the virus-specific CD8+ T cell response but does not compromise the host's ability to maintain pre-existing memory CD8+ T cells or to generate new memory CD8+ T cell responses against other pathogens.     

Predictors and markers of resistance to neurotropic nematode infection in rodent host

Parasite-mediated selection is currently believed to play an important role in life-history evolution. To assess how simple hematoserological and biochemical condition indices reflect host immunocompetence and infection resistance controlled laboratory experiments are required. We addressed these issues by infecting laboratory rats with the standard dose of embryonated eggs of a neurotropic nematode Toxocara canis. Urine baseline corticosterone concentrations, measured 1 week before infection, predicted the number of nematode larvae later recovered from host brains. Thus, this noninvasive clinical marker appeared useful for assessment of potential infection resistance. Rats who had accumulated high number of larvae in their brains and muscle had large spleens and high peripheral eosinophil counts 17 days postinfection. This finding is consistent with the concept that induction of eosinophilic Th2 type humoral immune response benefits the parasite rather than host. Hence, excessive peripheral eosinophilia and spleen enlargement are not markers of efficient antiparasite response in larval toxocariasis.     

Role for inducible costimulator in control of Salmonella enterica serovar Typhimurium infection in mice

Inducible costimulator (ICOS) is expressed on activated T cells and plays a key role in sustaining and enhancing the effector function of CD4 T cells. Given the function of this molecule in sustaining T-cell responses, we reasoned that ICOS might play an important role in a prolonged infection model, such as Salmonella infection of mice. To test this hypothesis, wild-type (WT) and ICOS-deficient (ICOS-/-) mice were infected systemically with a Salmonella enterica serovar Typhimurium strain expressing the chicken ovalbumin gene (Salmonella-OVA). ICOS-/- mice exhibited greater splenomegaly than WT mice and showed delayed bacterial clearance. The acquired immune response in this model was slow to develop. Maximal T-cell responses to Salmonella-OVA were detected at 3 weeks postinfection in both WT and ICOS-/- mice. CD4 T-cell-dependent gamma interferon production and a class switch to immunoglobulin G2a were severely reduced in ICOS-/- mice. ICOS-/- mice also exhibited a substantial defect in antigen-specific CD8 T-cell responses. In vitro, the effect of anti-ICOS on CD8 T-cell division was greater when CD8 T cells rather than CD4 T cells expressed ICOS, suggesting that the in vivo effects of ICOS on CD8 T cells could be direct. Taken together, these studies show that ICOS plays a critical role in control of Salmonella infection in mice, with effects on antibody, Th1, and CD8 T-cell responses.     

Cryopreservation and long-term in vitro maintenance of second-stage larvae of Toxocara canis

Second stage larvae of Toxocara canis were isolated from developed eggs, frozen in Eagle's Minimal Essential Medium with 5% dimethyl sulfoxide or 10% glycerol as cryoprotectants according to two cooling schedules and maintained in liquid nitrogen for 1 week. After thawing, the previously frozen larvae (FL) and unfrozen controls (CL) were maintained in a chemically defined medium in vitro for 35 weeks. While CL had motility rates around 95% to 97% throughout the experiment, previously frozen larvae (FL) exhibited rates of 48%–58% at the beginning and of 19%–39% at the end of the 35 week in vitro maintenance period. The surviving FL and CL larvae proved to be infective for mice. Excretory/secretory (ES) antigens isolated from several batches of culture medium in which FL and CL had been maintained reacted in the ELISA with human sera containing antibodies against Toxocara. Antigens from FL and CL separated by SDS-PAGE and silver-stained showed some differences in polypeptide patterns. Western-blot analysis revealed that these differences were not related to antigenic polypeptides but were most likely caused by substances without antigenic properties originating from dead and/or degenerating larvae. It can be concluded that ES antigens produced by previously frozen larvae are essentially the same as those derived from unfrozen controls.The value of cryopreservation of T. canis larvae for routine production of ES antigens will be further evaluated.     

Deletion of purE attenuates Brucella melitensis infection in mice.

We previously showed that a purE mutant (delta purE201) of Brucella melitensis 16M is attenuated for growth in cultured human monocytes (E. S. Drazek, H. H. Houng, R. M. Crawford, T. L. Hadfield, D. L. Hoover, and R. L. Warren, Infect. Immun. 63:3297-3301, 1995). To determine if this strain is attenuated in animals, we compared the growth of the delta purE201 mutant with that of strain 16M in BALB/c mice. The number of bacteria in the spleen and spleen weight peaked for both strains between 1 and 2 weeks postinfection (p.i.), though the number of delta purE201 cells was significantly less than the number of 16M cells recovered from the spleens of infected mice. During the next 6 weeks, delta purE201 was essentially eliminated from infected mice (three of five mice sterile; < 100 CFU in two of live mice at 8 weeks p.i.), whereas bacteria persisted at a high level in the spleens of 16M-infected mice (about 106 CFU per spleen). The number of bacteria in the livers and lungs of mice infected with either strain paralleled those in the spleen. Mice infected with 16M had a strong inflammatory response, developing dramatic and prolonged splenomegaly (five to eight times normal spleen weight) and producing serum interleukin-6. In contrast, mice infected with delta purE201 developed only mild, transient splenomegaly at 1 week p.i. and produced no interleukin-6 in their serum. We further characterized the host response to infection by measuring changes in immune spleen cell populations by flow cytometry. CD4- and CD8-positive lymphocytes declined by I week in both experimental groups, while MAC-1-positive cells increased. T-cell subpopulations remained low or declined further, and MAC-1 cells increased to three times normal levels during 8 weeks of infection with 16M but returned to normal by 4 weeks after infection with delta purE201. These results document infectivity and attenuation of delta purE201 and suggest that it should be further evaluated as a potential vaccine.     

Salmonella type III-mediated heterologous antigen delivery: a versatile oral vaccination strategy to induce cellular immunity against infectious agents and tumors

Salmonella type III secretion system (T3SS)-mediated translocation can be used for efficient delivery of heterologous antigens to the cytosol of antigen-presenting cells leading to prominent CD8 T-cell priming in orally immunized mice. The time point and duration of hybrid protein translocation during the Salmonella infection cycle can be modulated by employing various type III carrier molecules. The p60 protein of Listeria monocytogenes was used as model antigen to construct chimeric SspH2/p60. SspH2 is a “Salmonella pathogenicity island 2” (SPI2) protein that is known to be translocated by Salmonella during intracellular survival and replication in macrophages. This SPI2 carrier molecule is sufficient to induce a concomitant p60-specific CD4 and CD8 T-cell response in Salmonella-vaccinated mice. Moreover, T3SS-mediated antigen delivery results in an efficient priming of central and effector memory CD8 T cells in spleens of these animals. This vaccination strategy can also be employed to efficiently protect mice from an aggressive fibrosarcoma transfected with p60 in a prophylactic setting.     

Effect of various doses of infectiveToxocara canis andToxocara cati eggs on the humoral response and distribution of larvae in mice

The effect of 5–2,500 infectiveToxocara canis and 5–1,000T. cati eggs on the humoral immune response and on the distribution of larvae in the organism was studied in paratenic hosts — inbred C57BL6/J mice. With each dose ofT. canis eggs the maximal antibody level was recorded on day 56 post infection and was followed by a moderate decline that lasted until day 154 of the experiment. A correlation between the antibody level and the egg count was observed only with the infective dose of 5–50 eggs. A more rapid occurrence of antibodies was recorded in mice infected with a high dose of eggs. In those given 5 and 7T. cati eggs the antibody level exceeded the extinction threshold value only from day 21 to day 84. Low doses ofT. canis (n=5) andT. cati (n=7) eggs caused a comparable distribution of larvae in mice, and the larval recoveries on day 70 post infection ranged between 10.00% and 25.74%. Following a dose of 500T. cati eggs, 22.28% of the larvae were recovered, although only 1.08% were localized in the brain. A dose of 1,000T. canis eggs yielded, 36.37% of the larvae, with as much as 28.13% being found in the brain.     

Profound effect of the absence of IL-4 on T cell responses during infection with Schistosoma mansoni.

T cell responses of interleukin (IL)-4(-/-) and wild-type (WT) mice infected with the helper T cell 2 (Th2) response-inducing pathogen Schistosoma mansoni were compared. As expected, given the important role of IL-4 in Th2 response induction, the absence of IL-4 resulted in diminished Th2 responses, apparent as reduced production of IL-4, -5, and -10 by CD4(+) cells isolated from the spleens of infected IL-4(-/-) mice. Surprisingly, these cells produced significantly less interferon (IFN)-gamma and proliferated less than did those from infected WT mice after T cell receptor ligation. CD8(+) cells isolated from infected IL-4(-/-) mice also produced less IFN-gamma than WT CD8 cells, although there was no difference in the proliferative responses of these cell populations. After infection, spleens of infected IL-4(-/-) mice did not enlarge to the same extent as those of WT mice, and attrition of the CD8(+) cell population within this lymphoid organ was noted. Taken together, the data indicate that in addition to inhibiting Th2 response development, the lack of IL-4 during schistosomiasis significantly affects additional aspects of T cell responses.