Major Histocompatibility Complex Class I- And II-Deficient Knock-Out Mice Are Resistant to Primary but Susceptible to Secondary Eimeria Papillata Infections

Two distinct mechanisms seem to function in reducing oocyst output during Eimeria papillata infections in mice. For naive mice, immunity was afforded by a T-cell-independent gamma-interferon (IFN-γ) response mediated by natural killer (NK) cells. On reinfection, resistance was associated with T-cells and, to a lesser extent, perforin. To determine if antigen presentation with major histocompatibility complex (MHC) molecules was required to control oocyst production by NK cells during primary infection or by T-cells during secondary infection, mutant mice that lacked H2-IAβb (Aβb(-/-)) or β2-microglobulin (β2m(-/-)) were used. Since MHC molecules are required for the maturation of αβ T-cells, Aβb(-/-) and β2m(-/-) mutant mice are also deficient in functional αβ+ CD4+ or αβ+ CD8+ T-cells, respectively. As compared with wild-type control mice, oocyst output by mutant mice was not significantly affected during primary infection, suggesting that the ability of NK cells to control parasite replication is not dependent on the expression of MHC molecules. On reinfection, differences were observed for mutant mice as compared with controls. Aβb(-/-) mice were found to be more susceptible than β2m(-/-) mice, suggesting that the αβ+ CD4+ T-cell subset plays a greater role in resistance to reinfection than does the αβ+ CD8+ T-cell subset. The mechanism of resistance depends on the immune status of the host and requires the coordinated interaction of both αβ+ T-cell, subsets for optimal parasite control during subsequent infections

Ponazuril Inhibits the Development of Eimeria Vermiformis in Experimentally Infected Outbred Swiss Mice

We evaluated a 15% paste formulation of ponazuril in outbred Swiss mice that were experimentally infected with Eimeria vermiformis. Thirty, 8-week-old female mice (approximately 20 g) were placed in one group of 10 mice and one group of 20 mice. Mice in both groups were gavaged with approximately 5,000 sporulated oocysts of E. vermiformis on day 0. Mice in group 2 (n=10) were treated orally on days 3 and 4 with ponazuril (suspended in 30% propylene glycol) at the rate of 20 mg/kg. Mice in group 1 (n=20) were gavaged with a similar volume of 30% propylene glycol. Rates of oocyst passage (oocysts/g feces) were determined on day 10 (peak patency) for treated and nontreated mice using a fecal aliquot oocyst counting technique. Oocysts were not observed in the feces of treated mice using the aliquot technique. Control mice passaged oocysts at a geometric mean rate of \u3e104,000 oocysts/g feces. Control mice also produced significantly less feces on day 10. These results indicate that ponazuril is effective against E. vermiformis under the conditions utilized in this study, and that the E. vermiformis mouse model could be useful in predicting the efficacy of new anticoccidial drugs. © Springer-Verlag 2004

Parasite-Host-Cell Interactions of Eimeria papillata Sporozoites with Cultured Cells A Freeze-Fracture Study

The relationship between the sporozoite of Eimeria papillata and the host cell was studied by comparing the frequency and distribution of intramembranous particles (IMP) in their respective plasmalemmas before and after invasion. The entering sporozoite invaginates the host cell membrane during entry and this forms the boundary of the vacuole that encloses the parasite. Freeze-fracture replicas of this parasitophorous vacuole (PV) membrane showed a 3 fold decrease in IMP on the P- face (400 ± 215) and E-face (100 ± 29) when compared to the uninfected cell membrane (1369 ± 124 on the P-face and 395 ± 79 on the E-face). Studies of other coccidia and Plasmodium suggest that this considerable modification of the membrane appears to be the result of addition of proteins and lipids which are contributed by the invading parasite. The P- and E-faces of the plasmalemma of the free or internalized sporozoite was virtually unchanged. © 1993, Gustav Fischer Verlag Jena. All rights reserved

Ultrastructural Observations of Host-Cell Invasion by Sporozoites of Eimeria Papillata in Vivo

Scanning and transmission electron microscopy were used to study the invasion of mouse small-intestinal epithelium by sporozoites of Eimeria papillata. Some mice received oocysts by gavage and others received either sporocysts or sporozoites by direct injection into the small intestine. The highest concentration of invaded cells were found in ligated intestinal tissues studied at 5-45 min after the inoculation of sporozoites. Sporozoites actively invaded anterior end first, which resulted in extensive damage to the host cell. Such cells showed disrupted microvilli; protuberances of cytoplasm into the lumen, apparently the result of a disrupted plasma membrane; vacuolization of the cytoplasm; and damage to the mitochondria. These damaged cells were rapidly vacated as the sporozoite moved laterally into one or more adjacent intact host cells without entering the lumen. It is suggested that the host cell initially entered from the lumen becomes so severely traumatized that the parasite of necessity enters an adjacent cell as a prelude to further development. Various aspects of host-cell invasion by coccidia and malarial parasites are reviewed. © 1993 Springer-Verlag

Scanning and Transmission Electron Microscopy of Host Cell Pathology Associated with Penetration by Eimeria Papillata Sporozoites

Scanning and electron microscopy was used to study the pathogenesis that occurred in mouse epithelial cells that had been penetrated by Eimeria papillata sporozoites. Optimal penetration of parasites injected into nonligated and ligated mouse intestine was found to occur at 4-15 min post-inoculation. During initial penetration, the parasite caused disruption of the microvilli of the intestinal cells, which led to detachment of the microvilli from the plasma membrane of the penetrated cell. Host cells penetrated by the parasite showed extensive destruction of the internal cellular organization together with blebbing of host-cell cytoplasm and release of internal organelles such as mitochondria. Ultimately, the penetrated cells completely broke down, leaving vacuolated areas next to ultrastructurally normal epithelial cells. © 1992 Springer-Verlag

Cellular Dynamics and Cytokine Responses in BALB/c Mice Infected with Eimeria papillata During Primary and Secondary Infections

BALB/c mice were infected with the intestinal intracellular parasite Eimeria papillata to characterize lymphocyte responses and cytokine profiles throughout primary and secondary infections. Lymphocytes from the mesenteric lymph node (MLN) and the gastrointestinal tract (GIT) of infected mice were phenotypically analyzed using flow cytometry and immunofluorescence microscopy, respectively. Lymphocytes isolated from the MLN during primary infections of BALB/c mice with E. papillata do not proliferate, compared to day 0 uninfected controls, when stimulated in vitro with conconavalin A and express T(H)2-type cytokines (interleukin [IL]-4 and IL-10) on day 3 PI followed by the release of T(H)1-type cytokines (IL-2 and interferon-γ) during patency. In the small intestine, significantly more T cells and their subsets were observed during primary infection. During secondary infections, IL-2 was the only 1 of the 4 cytokines that was expressed earlier and at higher levels in the MLN when compared to primary infections. In the small intestine, significantly more αβ+ and CD8+ T lymphocytes were observed in mice during secondary infection. Oocyst antigens did not induce cellular proliferation at any time point during primary or secondary infections. We conclude that primary oral infection of BALB/c mice with E. papillata is associated with localized immunosuppression that may be mediated, in part, by early T(H)2-type cytokines. Immunity to secondary infection may be mediated by intestinal αβ+ CD8+ T lymphocytes through an IL-2 dependent mechanism

Light and Electron Microscopy Study of First Generation Development of Eimeria papillata (Apicomplexa: Eimeriidae) in Polarized MDCK-Cells in vitro

The early development of Eimeria papillata (Apicomplexa) was studied in vitro using light and electron microscopy. The first developmental stages observed were elongated, sporozoite-shaped schizonts with two nuclei and two refractile bodies which appeared 17 hours p.i.; the schizonts retained this shape until the 8-nuclei-stage. At 23 hours p.i. they had changed into a spherical shape, the refractile bodies had multiplied and the development of merozoites was observed. Each merozoite of the first generation contained two refractile bodies. An improved method for in vitro cultivation of Eimeria in polarized host cells and subsequent fine structural investigation is described © 1995, Gustav Fischer Verlag Jena. All rights reserved

Comparison of Four Murine Eimeria Species in Immunocompetent and Immunodeficient Mice

Factors associated with immune-mediated protection against coccidial parasites were examined in a series of experiments utilizing immunocompromised scid/scid(SCID) and scid/scid.beige/beige (SCID/Bg) mice, as well as immunocompetent BALB/c mice. Number of oocysts produced per g feces each day and prepatent and patent periods were assessed for 4 eimerian parasites (Eimeria papillata, Eimeria vermiformis, Eimeria falciformis, and Eimeria ferrisi) using the 3 murine strains. The number of infections required to elicit a protective immune response was also determined for each coccidial species in BALB/c mice. We report the first description of patent infections in inbred immunocompetent and immunodeficient mice infected with E. papillata. Results indicate that during primary infections, parasite replication is under partial immunological control for all Eimeria species. However, the control is mechanistically different for E. papillata because the adaptive immune response does not contribute to the control of primary infections. Both coccidial species infecting intestinal villar epithelial cells (E. papillata and E. ferrisi) were affected by the beige mutation using parasite output as an indicator, whereas E. falciformis, which infects intestinal crypt cells, is not. BALB/c mice were more resistant to challenge infections with upper intestinal parasites (E. papillata and E. vermiformis) in comparison to challenge infections with lower intestinal and cecal parasites (E. falciformis and E. ferrisi)