Susceptibility of five strains of mice to Babesia microti of human origin.

One outbred (CF1) and four inbred (BALB/c, C57, CBA and C3H) strains of mice were tested for susceptibility to Babesia microti of human origin. Of these, intact C3H mice developed higher parasitemia than all other intact mice, while BALB/c mice developed the highest parasitemia among splenectomized mice. Susceptibility was not related to H-2 haplotype in any obvious way. Because C3H and BALB/c mice developed relatively high initial peak parasitemias, the parasite was serially passaged in both of these mouse strains in an attempt to increase parasite virulence. After 30 passages in BALB/c and 49 passages in C3H mice over a period of 12 months, maximum parasitemias were 50 times higher than those observed initially. After the peak parasitemias of these two mouse-adapted parasites had stabilized, the relationship between onset and level of maximum parasitemia and number of parasites inoculated was determined. With both C3H- and BALB/c-adapted parasites, as inoculum size increased, the time required to reach maximum parasitemia decreased and the level of maximum parasitemia increased. Studies involving infection of either mouse strain with parasites adapted to the heterologous mouse strain indicated that C3H mice were more susceptible than BALB/c mice to homologous or heterologous parasites. These data suggest that the virulence of B. microti to the mouse can be increased by prolonged passage in this host. Once adaptation to this host species has occurred, virulence appears to be more dependent on the innate susceptibility of the mouse strain than on adaptation of the parasites to a particular strain of mouse.     

Trypanosoma musculi with Trichinella spiralis or Heligmosomoides polygyrus: concomitant infections in the mouse

Inbred mice infected with Trypanosoma musculi displayed wide variations in peak blood parasitemia. The most susceptible mice were C3H and A strain, while Balb/c, C57B1/6, and the related congenic B10 strains were the most resistant. The effect of an intestinal infection with either Trichinella spiralis or Heligmosomoides polygyrus on proliferation of T. musculi was investigated. T. spiralis infections given at the same time or up to 45 days before a T. musculi infection always caused an increase in blood parasitemia in C3H mice. Maximum increases were observed when T. spiralis infections preceded T. musculi by 5-10 days. In all mouse strains examined, dual infections increased maximum parasitemia by two- to four-fold, regardless of the degree of resistance of that mouse strain to either T. musculi or T. spiralis. This suggested that the immunological "cost" of a T. spiralis infection was the same for strains that were strong or weak responders to a primary infection with T. spiralis. In contrast, infection with H. polygyrus did not promote T. musculi parasitemia over the level of a single infection. The increase in blood parasitemia in T. spiralis-infected mice was largely due to the intestinal adult worm, but migratory larvae and mature muscle larvae also stimulated increased parasitemias. The increase in parasitemia was proportionate to the dose of T. spiralis, and the sex of the host did not affect the blood trypanosome level.     

Immunoregulation in murine malaria. Susceptibility of inbred mice to infection with Plasmodium yoelii depends on the dynamic interplay of host and parasite genes

Inbred and H-2 congenic mouse strains were tested for their ability to resist infections with the non-lethal 17X or with the lethal YM isolates of Plasmodium yoelii. DBA/2 and B10.D2 mice, which best resisted infections with non-lethal P. yoelii, were exquisitely susceptible to infection with lethal isolates of this malaria species. In contrast, B6 and B10 mice, which were susceptible to infection with non-lethal P. yoelii, were resistant to infection with the lethal isolates. This reversal of host response phenotype was influenced by H-2 genes, as evidenced by the divergent responses of the H-2 congenic strains B10 and B10.D2. However, a survey of mouse strains sharing common H-2 genes, but expressing different genetic backgrounds, demonstrated that genes outside the H-2 complex also influence the outcome of P. yoelii infections. By enumerating the numbers of P. yoelii-specific antibody-secreting cells in the spleens of infected mice, it was demonstrated that B6 mice, although susceptible to infection with non-lethal P. yoelii, nonetheless made a far stronger anti-parasite response after infection than did resistant DBA/2 mice. Using FACS analysis it was shown that infected B6 mice also produced large amounts of antibodies which bound to the surface of uninfected RBC. Thus, in B6 mice infected with non-lethal P. yoelii, a strong parasite-induced immune response was associated with susceptibility rather than resistance to infection. When T cell-deficient nude mice and their normal littermates were infected with the different isolates of P. yoelii, the nude mice had lower levels of parasitemia and higher RBC counts during the early stages of these infections, and lived longer than did normal littermates after infection with the lethal isolate. These data and the data from studies of B6 and DBA/2 mice support the idea that a strong immune response may be associated with susceptibility rather than resistance to P. yoelii, at least during the early stages of the infection. The finding that a single strain of mouse may present as resistant to infection with one P. yoelii isolate yet be exquisitely susceptible to infection with another suggests that the outcome of these murine malaria infections is dependent on a dynamic interplay between host and parasite genes. Thus, when genetic variability exists in both the host and the parasite populations, as would occur in nature, there may be little directed evolutionary change toward one phenotype or another.(ABSTRACT TRUNCATED AT 400 WORDS)     

Trypanosoma congolense: inheritance of susceptibility to infection in inbred strains of mice

Inbred strains of mice have shown marked differences in susceptibility to infection with Trypanosoma congolense, as judged by survival and levels of parasitemia. The underlying genetic basis of the susceptibility was examined with F1 hybrids and backcrosses derived from mouse strains of high and low susceptibility. The influence of H-2 haplotype on susceptibility was studied using H-2 congenic resistant strains of mice. F1 hybrids between the most susceptible strain (A/J) and the least susceptible strain (C57Bl/6) showed similar survival to that of the C57Bl/6 parent. This was reflected in a similar undulating pattern of parasitemia, although the level of parasitemia was consistently higher in the F1 hybrids than in the C57Bl/6. Backcrosses of the F1 hybrids with C57Bl/6 also had a similar pattern of parasitemia although there was a greater scatter in survival times so that a few animals survived longer than either of the parental strains. Backcrosses of F1 hybrids with A/J showed a range of survival times; approximately 25% of these animals died during the period when the A/J mice died, approximately 25% had a similar survival to that of C57Bl/6, while the remaining animals showed an intermediate duration of survival. All these backcrosses had a high initial peak of parasitemia; in about 70% of the mice the early parasitemia showed a distinct undulating pattern. F1 hybrids of A/J and C57Bl/6 with C3H/He mice, which are known to be of intermediate susceptibility, were also examined. The degree of dominance for low susceptibility was much less pronounced in these hybrid combinations than in the A/J × C57Bl/6 hybrids. The H-2 congenic resistant strains, all of which were on a C57Bl/10 genetic background, showed a similar pattern of parasitemia and survival. However, although the majority of all these strains survived for more than 100 days, there was a significant difference in survival between the C57Bl/10 mice and the H-2 congenic resistant strains. It was concluded that susceptibility of mice to T. congolense infection is likely to be under complex genetic control and that, at least in C57Bl/mice, H-2 haplotype has little influence on susceptibility.     

Cellular subsets involved in cell-mediated immunity to murine Plasmodium yoelii 17X malaria

Cell mediated immunity to nonlethal Plasmodium yoelli 17X (PY17X-NL) was examined in the CBA/CaJ mouse by adoptive transfer of sensitized T lymphocyte subsets. In intact mice, PY17X-NL causes a self-limiting infection with parasitemia levels ranging from 10 to 25% of total red blood cells. Upon recovery, mice are refractory to subsequent challenge with the homologous parasite. In T cell-depleted mice, PY17X-NL infections are extremely virulent and result in death of the host after parasitemia levels reach 50% or higher. The transfer of either Lyt-1 T cells or Lyt-2 T cells from immune animals into normal, naive animals produced accelerated recovery to subsequent infection. However, this adoptive transfer of immunity by either subset was dependent upon the presence of an I-J+, Lyt-null cell in the immune population. T cell deprivation precluded the ability of animals to control blood-stage infections. When T cell-depleted mice were reconstituted with naive, Ig-negative (T cell-enriched) spleen cells, parasitemia levels were controlled and the parasites were eliminated. When T cell-deprived animals were reconstituted with naive Lyt-1+2-, Ig-negative spleen cells, they experienced twofold higher parasitemias of longer duration than mice receiving unfractionated cells. Two of six of these Lyt-1 mice died of fulminant infections, suggesting that the presence of naive Lyt-2 cells enhances the degree of protection. Immune Lyt-2 T cells were highly protective in T cell-depleted animals. Protection by sensitized Lyt-1 T cells correlated with the induction of a monocytosis. On the other hand, protection by Lyt-2T cells occurred in the absence of monocytosis. The possibility that the immunity induced by each T cell subset is mediated by a different effector mechanism is discussed.     

Non-antibody-mediated control of parasitemia in acute experimental Chagas' disease

There appear to be two phases in the control of parasitemia in acute Chagas' disease in the mouse. The first phase occurs during the first few weeks after infection and control is achieved through a thymus-dependent, antibody-independent mechanism. Challenge of B cell-suppressed C3H and F1 (C57BL/6 X C3H) mice with the Brazil strain of Trypanosoma cruzi led to a course of parasitemia for the first 3 wk after infection similar to that seen in normal C3H or F1 mice and markedly lower than the parasite levels observed in the blood of nu/nu mice. Challenge of BXH-2 recombinant inbred mice resulted in a course of parasitemia similar to that seen in nu/nu mice up to day 16 despite the production of normal levels of antibody. The BXH-2 mice lack the ability to effect the early control of parasitemia. The second phase begins several weeks after infection with the rise in antibody titer, and the control is exerted through an antibody-mediated mechanism. In all B cell-suppressed mice, an inexorable rise in parasitemia occurred up to the time of death, which suggests that antibody is important for the eventual clearance of parasites from the blood. A comparison of the IgM and IgG antibody titers to T. cruzi in a series of resistant and susceptible strains showed that there was no correlation between the appearance of specific antibody or antibody titers and the levels of parasitemia observed. The level of parasitemia attained in the late acute phase may be primarily determined by the extent of parasite proliferation in the early acute phase.     

Biology of Borrelia hermsii in Kelly Medium

More than 800 Borellia hermsii in mouse plasma were required for establishment of growth in an artificial medium (Kelly), but only a single organism of a fully adapted strain (25th subculture) was required for a successful subculture. As judged by generation time, maximal concentration in culture, and length and motility of the organism, the process of adaptation extended through at least 11 subcultures. Because the organisms regularly died shortly after the logarithmic growth phase, transfers at 7- to 10-day intervals were required to maintain continuous cultures.     

Genetics of resistance to the African trypanosomes. V. Qualitative and quantitative differences in interferon production among susceptible and resistant mouse strains

The induction of interferon (IFN) was examined in different inbred mouse strains infected with Trypanosoma brucei rhodesiense. Relatively susceptible C3HeB/FeJ mice that do not exhibit variant-specific immunity or control parasitemia did not exhibit detectable IFN throughout the infection. Relatively resistant B10.BR mice that exhibit variant-specific immunity and control the first peak of parasitemia exhibited detectable IFN at two intervals. The appearance of IFN in B10.BR serum first coincided with the onset of the parasitemia 4 days after infection and then disappeared; this IFN peak was predominantly IFN-alpha/beta. The second time of appearance coincided with high titers of antibody and remission of the parasitemia. This IFN was predominantly IFN-gamma. Intermediately susceptible CBA/J mice also exhibited two detectable peaks of IFN; the first IFN-alpha/beta peak coincided with the onset of the parasitemia as in B10.BR mice. The second peak of IFN in the serum of CBA mice, however, was delayed in appearance and lower in concentration compared with B10.BR mice. This peak was characterized as being predominantly IFN alpha/beta. BALB/c mice (also intermediately susceptible) did not exhibit a first peak of IFN-alpha/beta production, but the second peak of IFN-alpha/beta production was similar to that seen in CBA mice. In contrast to infected mice, IFN was induced in both susceptible (C3H) and resistant (B10.BR) mice after immunization with glutaraldehyde-fixed trypanosomes or after chemotherapy of infection. We conclude that both the levels of IFN as well as the type of IFN induced during infection with T. b. rhodesiense depend upon the genetic background of the mouse strain infected. The induction of IFN-gamma in mice of the C57BL background may be linked functionally to more effective parasite control and to the presence of an effective immune response to T. b. rhodesiense.     

Immunity to Babesia bigemina in Experimentally Infected Cattle

Two groups of 5 and 6 Babesia bigemina“vaccine donor” animals of which 8 had been splenectomized were challenged 6 and 12 months respectively after they had lost their carrier state. All animals of the former, and 3 of the latter group survived; the remaining 3 animals succumbed to the challenge and died. It was concluded that premunity to B. bigemina is followed by sterile immunity which lasts for at least 6 months. Thereafter it fades gradually with time, depending on the immune response of the host, but can last for at least 12 months. Six splenectomized animals, which had lost their infectivity after treatment of their initial B. bigemina parasitemia at the rapidly rising phase with 1 mg/kg Berenil, died on challenge. It was concluded that a minimum period of contact between host and parasite is required for the acquisition of immunity to B. bigemina. Capillary tube agglutination titers were generally higher in the protected than in the unprotected animals. They remained fairly high for a long period after animals had lost their carrier state, which indicated the sensitivity of the CA test but rendered it unreliable for the detection of carrier animals.     

Trypanosoma congolense: Genetic control of resistance to infection in mice

Primary isolates of Trypanosoma congolense show a range of virulence in NMRI mice. Stabiliates derived from an isolate (Dinderesso/ 80/CRTA/3) which showed moderate virulence in most NMRI mice (moderate parasitemia and survival) were used in inbred mice. C57B1/6 were resistant with low parasitemia and survival. Parasitemias were higher in males than females. BALB/c were the most sensitive of the strains tested and died with fulminating parasitemia. Inheritance of resistance, defined as low parasitemia, was studied using these two strains. Male F1 showed high parasitemia; the backcrosses of F1 to the resistant parent had a ratio of one susceptible to one resistant product; the product of F1 to susceptible parent were all susceptible; and the F2 crosses showed a ratio of three susceptible to one resistant product. The results obtained with female F1, backcrosses, and F2 mice showed similar segregation to that found using males, but the range of parasitemia was always 1–2 log₁₀ lower, except for the F1 backcrossed to BALB/c, where female and male parasitemia were undistinguishable. The segregation ratios were identical whether resistant females were crossed with sensitive males or vice-versa. The results obtained are compatible with resistance being a recessive trait controlled by a single autosomal gene (or gene cluster). In addition, sex-associated factors appear to confer higher resistance in females.     

Chromosomal mapping of the host resistance locus to rodent malaria (Plasmodium yoelii) infection in mice

The disease outcome in malaria caused by the protozoan parasite Plasmodium is influenced by host genetic factors. To identify host genes conferring resistance to infection with the malaria parasite, we undertook chromosomal mapping using a whole-genome scanning approach in cross-bred mice. NC/Jic mice all died with high parasitemia within 8 days of infection with 1 x 10(5) parasitized erythrocytes. In contrast, 129/SvJ mice all completely excluded malaria parasites from the circulation and remained alive 21 days after infection. We performed linkage analysis in backcross [(NC/Jic x 129/SvJ)xNC/Jic] mice. The Pymr ( Plasmodium yoelii malaria resistance) locus was mapped to the telomeric portion of mouse Chromosome (Chr) 9. This locus controls host survival and parasitemia after infection. The Char1 locus ( P. chabaudi resistance locus 1), controlling host survival and peak parasitemia in P. chabaudi infection, was previously mapped to the same region. This host resistance locus mapping to Chr 9 may represent a ubiquitous locus controlling susceptibility to rodent malaria. Elucidation of the function of this gene will provide valuable insights into the mechanism of host defense against malaria parasite infection.     

Comparative virulence of three Trypanosoma evansi isolates from water buffaloes in the Philippines

The virulence of three Trypanosoma evansi isolates in Luzon, Visayas and Mindanao water buffaloes was compared determining the mortality rate, parasitemia level, clinical signs, and lesions on mice. A total of 51 inbred Balb/c mice (5-6 weeks old) were used and divided into two sets. Set A had three groups corresponding to three trypanosomes isolates (Luzon, Visayas, and Mindanao) with seven mice each whose parasitemia level, clinical signs, and lesions were noted at necropsy. Set B had three groups corresponding to the three isolates with ten mice each whose mortality was monitored. Each infected mouse was inoculated with 0.2 ml of T. evansi intraperitoneally and blood was examined under high power magnification. Their parasitemia level was determined using "Rapid Matching Method". Dead mice were subjected to necropsy and the lungs, liver, spleen, brain and heart were subjected to histopathological processing. Results showed that the mortality rate was highest at Day 3 for the Visayas isolates (70%), while at Day 5 for Luzon (90%) and Mindanao (70%) isolates. The parasitemia level of Visayas isolates (1×10(8.7)) reached the earliest peak at Day 4 while Luzon isolates (1×10(9)) at Day 6 and Mindanao isolates (1×10(8.7)) at Day 8. Statistical analysis using Least significant difference (LSD) revealed significant difference among treatment means at Days 2 and 4. All of the affected mice showed rough hair coat, decreased body weight, and decreased packed cell volume. The most obvious gross lesions observed were pale liver with petechiations and pale muscles. Histopathological examination revealed depletion of the red pulp and extramedullary hematopoiesis in the spleen. Congestion, intralesional trypanosomes in blood vessel and extramedullary hematopoiesis were observed in the liver. In the lungs non-specific lesions observed were pulmonary edema, congestion and hemosiderosis.     

Some Quantitative Aspects of the Adoptive Transfer of Immunity to Plasmodium berghei with Immune Spleen Cells

SYNOPSIS. Some of the parameters concerned in the adoptive transfer of immunity to P. berghei in rats have been studied. Immunity was not transferred efficiently until about 10 days after recovery of donor rats had commenced, but thereafter was very effective, even after the infection appeared to have been sterilized. Animals protected by a standard dose of cells from immune spleens but challenged with different doses of parasites attained a parasitemia of about 5% at different times, but all overcame the infection at the same time. Animals protected by different doses of cells from immune spleens and challenged with a standard dose of parasites, attained a parasitemia of about 5% simultaneously but the time taken to control the infection was inversely proportional to the dose of protective cells. Up to a parasitemia of about 5% there was no difference in the multiplication rate of parasites in control animals, in animals which were not effectively protected and in protected animals. Beyond a parasitemia of about 5% there was no difference in the multiplication rate of parasites in control animals and in animals which were not effectively protected. It is suggested that there is a critical period at a parasitemia of about 5% when the level of the immune response determines the fate of the host. At that stage the immune response may be inadequate, or possibly exhausted, and the parasite will then continue to multiply unchecked. Saturation of reticulocytes with parasites at a level of about 5% total parasitized red cells probably gives the host a respite which may allow the adoptively transferred cells to control the infection.     

Adaptation of Enterovirus 71 to Adult Interferon Deficient Mice

Non-polio enteroviruses, including enterovirus 71 (EV71), have caused severe and fatal cases of hand, foot and mouth disease (HFMD) in the Asia-Pacific region. The development of a vaccine or antiviral against these pathogens has been hampered by the lack of a reliable small animal model. In this study, a mouse adapted EV71 strain was produced by conducting serial passages through A129 (α/β interferon (IFN) receptor deficient) and AG129 (α/β, γ IFN receptor deficient) mice. A B2 sub genotype of EV71 was inoculated intraperitoneally (i.p.) into neonatal AG129 mice and brain-harvested virus was subsequently passaged through 12 and 15 day-old A129 mice. When tested in 10 week-old AG129 mice, this adapted strain produced 100% lethality with clinical signs including limb paralysis, eye irritation, loss of balance, and death. This virus caused only 17% mortality in same age A129 mice, confirming that in the absence of a functional IFN response, adult AG129 mice are susceptible to infection by adapted EV71 isolates. Subsequent studies in adult AG129 and young A129 mice with the adapted EV71 virus examined the efficacy of an inactivated EV71 candidate vaccine and determined the role of humoral immunity in protection. Passive transfer of rabbit immune sera raised against the EV71 vaccine provided protection in a dose dependent manner in 15 day-old A129 mice. Intramuscular injections (i.m.) in five week-old AG129 mice with the alum adjuvanted vaccine also provided protection against the mouse adapted homologous strain. No clinical signs of disease or mortality were observed in vaccinated animals, which received a prime-and-boost, whereas 71% of control animals were euthanized after exhibiting systemic clinical signs (P<0.05). The development of this animal model will facilitate studies on EV71 pathogenesis, antiviral testing, the evaluation of immunogenicity and efficacy of vaccine candidates, and has the potential to establish correlates of protection studies.     

Genetics of resistance to the African trypanosomes. VI. Heredity of resistance and variable surface glycoprotein-specific immune responses

The question of genetic linkage of parasite-specific immune responses to resistance to infection in experimental African trypanosomiasis was addressed. For this purpose, major histocompatibility complex-compatible resistant and susceptible inbred mouse strains and their F1 hybrid, F2 hybrid, and backcross offspring were infected with Trypanosoma brucei rhodesiense LouTat 1. Immunologic control of the first peak of parasitemia and survival times were the parameters measured. As we have reported previously (R. F. Levine and J. M. Mansfield, J. Immunol. 133:1564, 1984), B10.BR/SgSnJ mice are relatively resistant and controlled the growth of the infecting variant antigenic type (VAT) by mounting an antibody response to exposed epitopes of the variable surface glycoprotein (VSG). Fluctuating parasitemias resulting from sequential growth of different variable antigenic types occurred subsequently, and these mice died with a median survival time of 48 days. C3HeB/FeJ mice, relatively susceptible, did not control the infecting VAT and did not exhibit VSG-specific antibodies. These mice died with a median survival time of 22 days. The (B10.BR X C3H)F1 hybrids derived from crosses between resistant and susceptible mice all exhibited VSG-specific antibody responses and controlled the infecting VAT population. However, the median survival time of the F1 hybrids (24 days) was not significantly different from the survival time of the susceptible C3H parent. These findings demonstrate for the first time that antibody-mediated control of parasitemia is inherited as a dominant trait; that overall resistance, as measured by survival time, is inherited as a recessive trait (e.g., susceptibility is dominant); and that the two events segregate independently of one another. Further analyses of the inheritance of immunity and resistance (survival time) were made in which the F2 hybrid and backcross studies revealed that there are multiple genes controlling the VSG-specific antibody response as well as determining susceptibility. An extension of the present studies to a similar but non-major histocompatibility complex-mouse model system of resistance and susceptibility (C57BL/6J and C3H/HeJ mice, F1 hybrids, and 11 recombinant inbred B X H strains derived from them) was made in order to link the strain distribution patterns of known genetic markers with control of VSG-specific antibody responses or with control of susceptibility. Results of this study showed that resistance varied independently of the ability to control parasitemia with VSG-specific B cell responses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Plasmodium berghei: Isolation and maintenance of an irradiation attenuated strain in the nude mouse

An attenuated strain of malaria causing limited parasitemia in mice was derived from a highly virulent strain of Plasmodium berghei (NK65) which produced 100% lethality in mice. A pool of mouse blood infected with the original highly virulent P. berghei was exposed to 40 Krad irradiation and parasites were inoculated into nude mice as well as into thymus competent normal littermates. Thymus competent mice showed no parasitemia, while one out of the five nude mice inoculated with the irradiated parasites developed a slow and progressive parasitemia. These parasites induced a self-limiting parasitemia in thymus competent mice, even when a large inoculum was administered. Maintenance of the low virulence strain required passage through nude mice. After 50 passages at two weekly intervals, reversion to virulence did not occur. A single vaccination with the attenuated strain induced immunity in mice against a challenge inoculation with the original virulent strain. Specific IgG persisted at high titer for more than 9 weeks in mice receiving a single inoculation of the attenuated strain.     

Lymphoid organ alterations enhanced by sub-lethal doses of coronaviruses in experimentally induced Trypanosoma cruzi infection in mice

The effect of sub-lethal doses of coronaviruses on the course of disease in CBA mice experimentally infected with a mildly pathogenic strain of Trypanosoma cruzi was investigated. Mice were inoculated with either T. cruzi, 0.1 median lethal dose (LD50) of coronavirus (mouse hepatitis virus [MHV-3] or virus X), or both pathogens. Levels of parasitemia, mortality, and the extent of pathologic alterations in lymphoid organs were determined. Mice inoculated with T. cruzi had mild alterations in their lymphoid organs and survived infection. In contrast, mice inoculated with both pathogens died, and had significantly higher levels of parasitemia and profound alterations in lymphoid organs. These results indicate that the pathologic profile of T. cruzi infection can be profoundly altered by subclinical infection with coronaviruses.     

Trypanosoma cruzi (kinetoplastida Trypanosomatidae): biological heterogeneity in the isolates derived from wild hosts

The course of experimental infection of Swiss mice with 95 sylvatic Trypanosoma cruzi isolates included in TCI or TCII genotype was characterized. The purpose was to verify biological properties and its eventual correspondence with original host species, genotype or zymodeme. The isolates of T. cruzi were 100% infective, 55% resulted in patent parasitemia with 69% (36/52) of mortality. A meaningful biological heterogeneity was observed in both, TCI and TCII isolates. TCII isolates resulted in higher patent parasitemia 64% (38/59), in contrast to the 41% TCI infected Swiss mice (14/34). Parasitemia was not always associated to mortality. Higher biological heterogeneity was observed in T. cruzi II isolates derived from L. rosalia from the Atlantic Coastal Rain forest. TCII isolates derived from marsupials resulted in very similar infection profile in Swiss mice.     

IFN-gamma-dependent nitric oxide production is not linked to resistance in experimental African trypanosomiasis

Resistance to African trypanosomes is dependent on B cell and Th1 cell responses to the variant surface glycoprotein (VSG). While B cell responses to VSG control levels of parasitemia, the cytokine responses of Th1 cells to VSG appear to be linked to the control of parasites in extravascular tissues. We have recently shown that IFN-gamma knockout (IFN-gamma KO) mice are highly susceptible to infection and have reduced levels of macrophage activation compared to the wild-type C57BL/6 (WT) parent strain, even though parasitemias were controlled by VSG-specific antibody responses in both strains. In the present work, we examine the role of IFN-gamma in the induction of nitric oxide (NO) production and host resistance and in the development of suppressor macrophage activity in mice infected with Trypanosoma brucei rhodesiense. In contrast to WT mice, susceptible IFN-gamma KO mice did not produce NO during infection and did not develop suppressor macrophage activity, suggesting that NO might be linked to resistance but that suppressor cell activity was not associated with resistance or susceptibility to trypanosome infection. To further examine the consequence of inducible NO production in infection, we monitored survival, parasitemia, and Th cell cytokine production in iNOS KO mice. While survival times and parasitemia of iNOS KO mice did not differ significantly from WT mice, VSG-specific Th1 cells from iNOS KO mice produced higher levels of IFN-gamma and IL-2 than cells from WT mice. Together, these results show for the first time that inducible NO production is not the central defect associated with susceptibility of IFN-gamma KO mice to African trypanosomes, that IFNgamma-induced factors other than iNOS may be important for resistance to the trypanosomes, and that suppressor macrophage activity is not linked to either the resistance or the susceptibility phenotypes.     

Protection against malaria by anti-erythropoietin antibody due to suppression of erythropoiesis in the liver and at other sites

We have previously reported that erythropoiesis commences in the liver and spleen after malarial infection, and that newly generated erythrocytes in the liver are essential for infection of malarial parasites as well as continuation of infection. At this time, erythropoietin (EPO) is elevated in the serum. In the present study, we administered EPO or anti-EPO antibody into C57BL/6 (B6) mice to modulate the serum level of EPO. When mice were infected with a non-lethal strain (17NXL) of Plasmodium yoelii (blood-stage infection of 10(4) parasitized erythrocytes per mouse), parasitemia continued for 1 month, showing a peak at day 17. Daily injection of EPO (200 IU/day per mouse) from day five to day 14 prolonged parasitemia, whereas injection of anti-EPO antibody (1.5 mg/day per mouse) every second day from day five to day 28 decreased it. Erythropoiesis was confirmed in the liver, spleen and bone marrow by the appearance of nucleated erythrocytes (TER119+). When anti-EPO antibody was injected by the same protocol into mice infected with a lethal strain (17XL) of P. yoelii, all mice showed decreased parasitemia and recovered from the infection. These results suggest that the use of anti-EPO antibody after malarial infection may be of therapeutic value in severe cases of malaria.