Effect of temperature and clofibrate on Plasmodium berghei infection in mice.

Parasitemia counts established that 22 degrees C-acclimated mice subjected to cold exposure for a short time (-35 degrees C for 30 min) during Plasmodium berghei infection had significantly higher parasitemia levels than parasitized mice continuously housed at 22 degrees C. Parasitized 5 degrees C-acclimated mice also demonstrated higher parasitemia levels than parasitized 22 degrees C-acclimated mice. There was no correlation between plasma free fatty acid (PFFA) concentration and parasitemia in mice infected with P. berghei. The effect of clofibrate (an agent known to reduce PFFA levels in rats) in reducing PFFA levels in mice was inconclusive. However, the P. berghei-infected mice treated with clofibrate demonstrated significantly lower parasitemia when compared to parasitized mice that were not treated with clofibrate.     

Inheritance of post-vaccinal resistance against Plasmodium berghei infection in mice

The protective effect of specific vaccination against Plasmodium berghei (P. berghei) was compared in terms of survival percentage in DBA/2, C3H, outbred albino mice and in two lines of mice produced by selective breeding for either high or low antibody responsiveness to sheep erythrocyte (H and L lines respectively). The efficacy of induced protection varies according to genetic constitution. It is very strong in H line and albino mice, intermediate in DBA/2 and very weak in L line and C3H. The inheritance of post-vaccinal resistance to infection was studied in F1 hybrids and backcrosses between C3H and the other lines. The control was polygenic in all cases. The dominance of the characteristic depends on the strain combination. On the whole the results suggest the non-identity of the genes controlling protection in the various lines. The lack of a quantitative parameter for a more precise genetic analysis of protective immunity in inbred lines is stressed, since both anti-P. berghei antibody production and parasitaemia proved to be unreliable.     

Plasmodium berghei: pulmonary oedema and changes in clotting and fibrinolysis during infection in mice

Mice infected with Plasmodium berghei, during the ten days of infection, showed significant pulmonary oedema, delayed activated partial thromboplastin time, augmented plasma fibrinolytic activity, oscillations in fibrinogen and unchanged plasminogen levels. These alterations can be expected to cause the release of inflammatory peptides, leading to increased vascular permeability and the generation and/or maintenance of the pronounced pulmonary oedema affecting these animals.     

Anti-malarial activity of Eclipta alba against Plasmodium berghei infection in mice

The anti-malarial activity of Eclipta alba leaves extract was evaluated against Plasmodium'berghei ANKA strain in mice. A standard inoculum of 1 x 10(6) infected erythrocytes was used. The methanolic leaf extract (250-750 mg/kg) produced a dose-dependant chemosupression or schizontocidal effect during early and established infection and high mean survival time (m.s.t.) values particularly in the group administered 750 mg/kg/day of extract. The plant extract also exhibited repository activity. The results of the preliminary studies carried out with E. alba are encouraging, which can be exploited in malaria therapy.     

Protective and pathological activity in serum of mice developing resistance to Plasmodium berghei infection

Summary The serum from mice developing resistance against Plasmodium berghei infection using chemotherapeutic treatment has been analysed in vivo and in vitro. During the immunization period pathological as well as protective activities which could be transferred by serum were generated. The pathological activity, which was defined as destruction of erythrocytes in normal recipient mice, was generated early in the immunization procedure, peaked at day 21, and decreased to undetectable levels by day 35. After reinfection of the donor mice the pathological activity reappeared in the serum, and was maintained for at least 56 days. Analysis of the transferred serum samples showed the presence of anti-erythrocyte antibodies (ELISA), but no correlation with the in-vivo anti-erythrocyte effect could be found. The anti-erythrocyte effect of the serum samples indirectly increased the parasitaemia in the recipient mice through the induction of reticulocytosis. The protective effect of the serum samples could only be detected in samples taken from animals beyond day 61 of the immunization procedure. This net protective effect was reflected in a decreased parasitaemia at 7 days after challenge of the recipient mice with P. berghei infected erythrocytes. The protective activity of the serum was correlated with high titres of anti-erythrocyte antibodies. Anti-erythrocyte antibody titres were strongly correlated with titres against heterologous red blood cells as well as total immunoglobulin content of the serum samples, indicative of polyclonal activation of lymphocytes. Except for IgGl, all (sub-) classes were elevated during the immunization procedure, of which IgG3 was abundant. After immunity was obtained these immunoglobulin levels remained high, and the relative amount of IgGl in the serum was restored.     

Differential interleukin-10 expression in interferon regulatory factor-1 deficient mice during Plasmodium berghei blood-stage infection

Mice deficient of functional interferon regulatory factor-1 (IRF-1-/-) by targeted gene disruption infected with a lethal murine malaria strain, Plasmodium berghei ANKA survived longer than its wild-type littermates despite the inability to induce appreciable amounts of interferon-gamma (IFN-gamma) and nitric oxide. In addition, infected IRF-1-/- mice displayed less organ injury with reduced necrosis and inflammation. Both wild-type and IRF-1-/- mice treated with exogenous interleukin-12 (IL-12) suffered extensive organ damage with corresponding up regulation of IFN-gamma, suggesting the pathogenic potential of IL-12 and IFN-gamma. IL-10 is a cytokine produced by CD4+ T lymphocytes belonging to the Th2 subset. Expression of IL-10 in the wild-type mice correlated with the severity of the infection, with higher mRNA expression towards the later stage of infection. In contrast to the wild-type mice, IL-10 levels in the IRF-1-/- mice were induced early in the infection and decreased gradually as the infection progressed. Both untreated and IL-12 treated wild-type mice appeared to follow a Th1-like immune response early in the infection and a Th2-like immune response later in the infection. However, the IRF-1-/- mice were able to launch an altered immune response with a Th2-like immune response early in the infection. These findings suggest that IL-10 expression in the IRF-1-/- mice during the early stage of P. berghei ANKA infection could play an important role in suppressing pathogenic effects of a cell mediated immune response and promoting protective immunity against the parasite.     

Survival of parasites in mice immunized against Plasmodium berghei.

The rodent malaria parasite Plasmodium berghei may survive im immunized Swiss and C3H/StZ mice for a considerable period of time. Despite considerable differences in the observed survival time in animals of a given strain, a general, strain specific pattern is observed. Parasites generally survive longer in Swiss than in C3H/StZ mice. In some of the Swiss mice parasites survived throughout the experimental period, whereas in the others restricted survival was observed, possibly reflecting genetic disparity. Since booster infections did not affect the survival pattern, the effectiveness of elimination is not determined by "antigen" dependent, gradual differences in quality of the hosts' immune response. Repeated biotechnical manipulation of the animals may influence experimental results.     

伯氏疟原虫对小鼠脾B细胞和自然杀伤细胞及其表面分子的影响

为探讨伯氏疟原虫对小鼠脾B细胞和自然杀伤(NK)细胞及其表面分子的影响,将10只雌性C57BL/6小鼠随机分为健康对照组和感染组,每组5只。感染组小鼠经尾静脉注射伯氏疟原虫(106个/鼠)进行感染,健康对照组注射等量生理盐水。感染后6 d,取小鼠脾,制备单细胞悬液,采用流式细胞术检测小鼠B细胞和NK细胞的含量及其表面分子CD62L、CXCR3、CD69的表达水平。结果显示,感染组小鼠脾B细胞百分比含量为(79.2±3.6)%,高于健康对照组的(54.3±4.4)%(P<0.01);感染组脾NK细胞百分比为(2.2±0.7)%,低于健康对照组的(4.6±0.8)%(P<0.01)。CD62L在感染组B细胞中的百分比为(77.7±4.4)%,高于健康对照组的(72.8±7.1)%,但二者差异无统计学意义(P>0.05);CD62L在感染组NK细胞中的百分比为(61.9±4.8)%,低于健康对照组的(86.6±4.2)%(P<0.01)。CXCR3在感染组B细胞中的百分比为(4.1±0.1)%,高于健康对照组的(3.0±0.2)%(P<0.01);CXCR3在感染组NK细胞中的百分比为(2.1±0.9)%,低于健康对照组的(2.3±0.4)%,但二者差异无统计学意义(P>0.05)。CD69在感染组B细胞和NK细胞中的百分比分别为(54.3±4.7)%、(22.2±1.6)%,均高于健康对照组的(1.9±0.4)%、(1.3±0.3)%(P<0.01)。提示感染疟原虫的小鼠可能通过增加B细胞的数量以及上调其表面分子CXCR3和CD69及NK细胞表面分子CD69的表达水平发挥抗疟作用。     

Serum-soluble malarial antigens and immune complex nephritis in Plasmodium berghei berghei infected mice.

Swiss albino mice infected with Plasmodium berghei berghi showed the serum-soluble malarial antigen and antibody on day 10 of infection onward. Immune complex nephritis in these mice developed on the seventh day after inoculation. The infected kidneys revealed the deposition of mouse gamma globulin, mouse beta1C globulin and malaria antigen along the capillary wall of the glomeruli. Proteinuria was detected on seventh day of infection. Serum-soluble malaria antigen in probably responsible for forming the soluble immune complex which causes glomerulonephritis in infected mice.     

Adoptive transfer of immunity to Plasmodium berghei with spleen cells from drug cured mice

Plasmodium berghei infection gives rise to a fatal fulminating parasitaemia in mice. Resistance to the infection can be achieved if the mice are allowed to recover from the blood-induced infection by administration of chloroquine. In CBA/Caj, one cycle and in Balb/c mice, at least, two cycles of infection, alternating with drug-cure were necessary for the establishment of immunity. No parasitaemia was seen following further challenges after the third infection. Adoptive transfer of spleen cells from the immune mice showed that immunity could be transferred by 50 to 70 x 10(6) cells. On challenge the recipients develop high parasitaemia which was cleared in less than 5 weeks. Recipient mice given low number of spleen cells did not survive. The transfer of immune spleen cells depleted of either T or B lymphocytes abrogated the protective effect. Comparatively T lymphocytes were less effective in transferring protection than B lymphocytes. The study suggests that both humoral and cell-mediated effector mechanisms are needed for the maintenance of immunity in drug-cured immune mice.     

In vitro cultivation of the exoerythrocytic stage of Plasmodium berghei in irradiated hepatoma cells

Growth of cultures of human hepatoma cells was inhibited by exposure to doses of gamma irradiation as low as 1,000 rad., and the monolayers remained viable for up to 35 days. Irradiated cells were at least as susceptible to Plasmodium berghei sporozoite invasion as non-irradiated cells, and supported the entire exoerythrocytic cycle producing more infectious merozoites. Irradiated cultures may have use for culture of human malarias, and drug studies requiring synchronous cultures.     

Effects of immune complexes on immunity to Plasmodium berghei infection

The ELISA test titers and RIPA patterns of sera collected from vaccinated and non-vaccinated rats during P. berghei infection were similar. The sera collected just after clearance of parasitemia from the vaccinated rats, but not that from the non-vaccinated rats protected mice in passive protection tests. After precipitation to remove immune complexes, the sera from the non-vaccinated rats also protected mice. Administration of acute phase serum early in the course of infection aggravated parasitemia and delayed recovery from P. berghei infection in rats. Administration of hyperimmune serum early in the course of infection initially reduced parasitemia but then delayed recovery of rats from P. berghei infection. These results suggest that immune complexes may interfere with antibody mediated immunity to P. berghei and may also retard development of the induced immune response.     

Distinct host‐related dendritic cell responses during the early stage of Plasmodium yoelii infection in susceptible and resistant mice

The diverse outcomes of experimental murine infection with Plasmodium parasites, ranging from spontaneous cure to death, depend largely on the establishment of an effective Th1 immune response during the early stages of infection. However, the molecular and cellular factors responsible for the induction and regulation of this response are poorly understood. As immunity is initiated by dendritic cells (DCs), we compared their phenotype and function during the early stages of infection with Plasmodium yoelii 17XL (P.y 17XL) strain in susceptible (BALB/c) and resistant (DBA/2) mice. Resistant DBA/2 mice developed a greater number of myeloid (CD11c⁺CD11b⁺) and mature DCs, which were fully functional and capable of secreting IL‐12p40. In contrast, susceptible BALB/c mice produced more plasmacytoid (CD11c⁺CD45R/B220⁺) and less mature DCs, resulting in high levels of IL‐10 and TGF‐β1. In addition, an in vitro experiment confirmed that splenic DCs from the two strains of mice differ in their ability to prime CD4⁺T cells in response to P.y 17XL stimulation. These findings indicate that the subset, the phenotype and the type of inflammatory and anti‐inflammatory signals of splenic DCs are critical factors responsible for the discrepancy in the ability to induce or regulate Th1 immune responses in different hosts.