Xanthoquinodin B3, a new anticoccidial agent produced by Humicola sp. FO-888

Xanthoquinodin B3, a new component of anticoccidial xanthoquinodins, which was detected in the culture broth of Humicola sp. FO-888, was isolated by heat treatment of the xanthoquinodins complex. Structural elucidation indicated that xanthoquinodin B3 has the same heterodimer of xanthone- and anthraquinone-derived monomers as other xanthoquinodins. Schizont formation of monensin-resistant Eimeria tenella in BHK-21 cells was inhibited by xanthoquinodin B3 at concentrations greater than 0.035 microM.

Increasing the yield of Eimeria tenella oocysts in primary chicken kidney cells

The present study was undertaken to increase the yield of Eimeria tenella oocysts in primary chicken kidney cells (PCKCs) using a comparatively inexpensive cell-culture system. PCKCs growing on coverslips positioned on the bottoms of individual wells in 24-well tissue-culture plates were infected with sporozoites of E. tenella. The effects of changing the culture medium (RPMI 1640), medium pH, serum type, and serum concentration in the wells were determined by counting newly produced oocysts at 7 days postinoculation. There were significantly more (P < 0.01) oocysts produced when the medium was supplemented with 10% fetal bovine serum (FBS) and changed either daily or every other day compared with not changing the medium. When the same medium was changed daily, significantly more (P < 0.05) oocysts were produced at pH 7.4 than at pH 8.0 but not at pH 6.0. If the medium was changed daily, significantly more (P < 0.05) oocysts were produced when medium was supplemented with 10% FBS only rather than 5% and 10% chicken serum. The cell-culture system described in this study offers a convenient and efficient method for investigating the biological, biochemical, and immunological relationships between E. tenella and the host cell.

In vivo role of tumor necrosis-like factor in Eimeria tenella infection

The effect of tumor necrosis-like factor (TNLF) on the pathogenesis of coccidiosis was investigated. Injection of crude chicken TNLF enhanced the weight loss caused by Eimeria tenella infection. Rabbit polyclonal antibody against recombinant human tumor necrosis factor-alpha (rhTNF) partially restored E. tenella-induced weight loss in SC chickens, but not in TK chickens. However, injection of chickens with chicken TNLF, rhTNF, and rabbit serum against rhTNF had no significant effect on cecal lesions. Both SC and TK chickens produced circulating TNLF following primary, but not secondary infection, and SC chickens showed higher level of TNLF production than TK chickens. Peripheral blood leukocyte-derived macrophages from SC and TK chickens produced a significant amount of TNLF compared to the preinfection condition when cocultured with sporozoites. In general, macrophages from SC chickens produced higher levels of TNLF than those from TK chickens. No significant difference was observed between primary and secondary infection. These results suggest that the excessive TNF production may be involved in weight loss caused by E. tenella infection in SC chickens.

Eimeria tenella and E. acervulina: differences in ability to elicit cross-species protection as compared with the turkey coccidium, E. adenoeides

Repeated oral inoculation of turkey poults with large doses (1 x 10(6) oocysts) of the chicken coccidia, Eimeria tenella or E. acervulina, failed to prevent weight loss, poor feed conversion, and intestinal pathology in turkeys challenged with the turkey coccidium, E. adenoeides. Invasion by E. tenella in turkeys was significantly greater than invasion by E. adenoeides in chickens; by 24 hr postinoculation (PI), the numbers of E. tenella and E. adenoeides sporozoites in the ceca had decreased markedly as compared with the numbers that initially invaded, and they did not differ significantly from each other. At 24 hr PI, however, transfer of cecal scrapings from chickens or turkeys inoculated with E. adenoeides produced infection in 53% of the recipient turkeys, but transfer of scrapings from either chickens or turkeys inoculated with E. tenella failed to produce infection in 20 attempts with recipient chickens. Cultured chicken peripheral blood monocytes (PBMs) that were inoculated with E. adenoeides sporozoites contained numerous vesicles that were recognized by the refractile body-specific monoclonal antibody 1209; the number of vesicles was markedly decreased in PBM cultures inoculated with gamma-irradiated E. adenoeides sporozoites. Very few vesicles were detected in the cytoplasm of turkey PBMs that contained E. tenella sporozoites, and none were detected in turkey PBMs containing E. adenoeides sporozoites. The survival of infective sporozoites, along with the secretion of refractile body antigen, may be more critical to the development of cross-species immunity than the number of sporozoites that initially invade the foreign host.

Selective labeling of intracellular parasite proteins by using ricin

Studies focused on the synthesis by intracellular parasites of developmentally regulated proteins have been limited due to the lack of a simple method for selectively labeling proteins produced by the parasite. A method has now been developed in which ricin is employed to selectively inhibit host-cell protein synthesis. Ricin is a heterodimer composed of two subunits, a lectin and a glycosidase, and it binds to terminal galactose residues on the cell surface via the lectin. Following endocytosis of the intact molecule, a disulfide bond linking the two subunits is cleaved, and only the glycosidase subunit enters the cytoplasm, where it inhibits cytoplasmic protein synthesis by catalyzing the cleavage of the 28S rRNA. Due to the loss of the receptor-binding lectin subunit, ricin cannot permeate host-cell mitochondria or intracellular parasites, and, therefore, protein synthesis within these compartments continues uninterrupted. This system has been used to selectively label parasite proteins from Eimeria tenella and Toxoplasma gondii by using the avian cell line DU-24. In these cells, mitochondrial protein synthesis was inhibited by using chloramphenicol. The use of the avian rho0 cell line DUS-3 provided an additional advantage, because these cells lack mitochondrial DNA. Therefore, those proteins radiolabeled with [35S]methionine/cysteine in ricin-treated, parasite-infected rho0 cells are exclusively those of the intracellular parasite. This technique should be applicable for studying protein synthesis by other intracellular parasites.

Ultrastructural observations of development of Eimeria tenella in a novel established avian-derived cell line

Transmission electron microscopy was used to study the in vitro development of Eimeria tenella in a novel established avian-derived cell line (designated CEV-1/F7) used for antigen production in chicken immunization studies. Sporozoites of E. tenella were inoculated onto cell monolayers and the cells were fixed at 24-h intervals. Large numbers of intracellular sporozoites were seen at 24 h postinoculation (p.i.), and trophozoites were identified at 24-48 h p.i. Immature schizonts, some with budding merozoites, were seen by 48 h p.i. At 72-96 h p.i., immature and mature schizonts and extracellular merozoites were observed. No merozoite invasion occurred, but immature second-generation schizogony was seen in parasitophorous vacuoles of first-generation schizonts. No further development occurred and degeneration of most schizonts was seen by 120-144 h p.i. The results confirmed synchronous development of E. tenella until 48 h p.i., followed by asynchronous development and ultrastructural degeneration with increased incubation time.

Inhibition of the in vitro development of Eimeria tenella in chick kidney cells by immune chicken splenocytes

An in vitro microbicidal assay was used to study the immune response of chickens to Eimeria tenella by measuring the effect of splenocytes from immunized chickens on intracellular development of E. tenella. Splenocytes were prepared from specific-pathogen-free chickens [strain P2a(B19B19) or N2a(B21B21)], immunized one, two, or three times with non-lethal doses of E. tenella. Twelve hours following infection of chick kidney cells (CKCs) with E. tenella sporozoites, splenocytes were added to infected CKCs for 4, 8, or 36 hours. Intracellular E. tenella development was allowed to continue until 72 hours after sporozoite infection, when intracellular development was quantitated by counting merzoites. Immune splenocytes significantly inhibited E. tenella intracellular development after one, two, or three immunizations. Significant inhibition occurred with 4, 8, or 36 hours of coculture and was no greater with longer co-culture times. Immune P2a splenocytes significantly reduced merozoite development in both syngeneic P2a and allogeneic N2a infected CKCs, whereas immune N2a splenocytes had little effect on E. tenella development in either N2a or P2a infected CKCs. These results suggest that immune splenocytes are induced and act relatively rapidly and are not apparently restricted by the major histocompatibility complex, consistent with natural killer cell activity.

In vitro and in vivo immunolabeling of sporozoites, schizonts, and sexual stages of Eimeria acervulina and E. tenella by a species- and stage-cross-reactive monoclonal antibody

A cross-reactive monoclonal antibody (mAb), designated 1205, was used to study redistribution, parasitophorous vacuole (PV) incorporation, and in situ antigen production during the intracellular parasite development of Eimeria acervulina and E. tenella. Western-blot analysis of sporozoite preparations showed that the mAb recognized antigenic bands at 55 and 80 kDa. Indirect immunofluorescent antibody (IFA) labeling of sporozoites produced an internal dot pattern. Immunogold electron microscopy (IM) showed labeling of dense granules within sporozoites. The IFA pattern changed to a general-internal label in immature schizonts followed by a surface-tip pattern in mature merozoites both in vitro and in vivo. IM of the asexual stages revealed the same labeling pattern for the in vivo development of both species, and labeling of rhoptries was seen. In vitro, the PV membrane together with amorphous material within the PV was labeled by IFA during schizont development for E. tenella. No IM labeling of either the PV membrane or material within the PV was observed. Sexual stages seen in vivo for both species had the general-internal IFA pattern.

Oxygen concentration and asexual development of Eimeria tenella in cell cultures

Primary chicken kidney cells in Flexiperm cultures were either inoculated with Eimeria tenella sporozoites or incubated as noninoculated controls. Oxygen concentration was reduced (10 or 15 vol% O2, 5 vol% CO2) or increased (25 or 30 vol% O2, 5 vol% CO2) in a triple gas incubator (Heraeus B 5061 EK/O2) and retained in a CO2-air incubator (20 vol% O2, 5 vol% CO2) 24 hours post inoculation (hpi). Mature second generation schizonts (mS2) were counted microscopically at 120 hpi and numbers were compared either as mS2 or mS2/cm2 confluent cells. Asexual development of Eimeria tenella was neither stimulated nor inhibited by different oxygen concentrations, indicating that higher numbers of schizonts in cultures under reducing conditions reported earlier are probably a result of increased invasion rates of sporozoites.

Comparative development of Eimeria tenella in primary chick kidney cell cultures derived from coccidia-resistant and -susceptible chickens

A sixfold difference in resistance to coccidia (Eimeria tenella) infection between a resistant and a susceptible line of Auburn White Leghorn chickens, derived by selective breeding, has been reported. The purpose of the following study was to determine whether the resistance or susceptibility phenomenon in the Auburn lines could be manifested in a homogeneous group of isolated host kidney cells that support E. tenella development in vitro but not normally in vivo. Propagation of the parasite in host cells in vitro eliminates humoral and cellular elements of immunity, and allows the study of host genetic influences at the cellular level. Differences in parasite development were examined between the two lines of cells in vitro after 48 and 96 h of incubation; time periods that reflect initial infection of the host cells by the parasite and the subsequent asexual development. Quantification of differences by liquid scintillation counting was based on parasite-specific incorporation of pyrimidines, specifically [3H]-uracil. The results supported previous findings that overall E. tenella development was significantly greater in the host cells from the susceptible line than in the cells from the resistant cultures at both time periods.

Cultivation of Eimeria tenella in Japanese quail embryos (Coturnix coturnix japonica)

Complete development of Eimeria tenella in Japanese quail embryos was observed. Sporozoites were inoculated into the allantoic cavity of 7-day-old Japanese quail embryos (Coturnix coturnix japonica), after which the infected embryos were incubated at 41 C. In the chorioallantoic membrane mature first generation schizonts, mature second generation schizonts, and gametes were detected at 48 hr postinoculation of sporozoites (PI), 84 hr PI, and 126 hr PI, respectively. Mature gametes and zygotes were found at 132 hr PI, and oocysts were detected at 138 hr PI. Mortality of embryos increased with increment of inoculum size of sporozoites. LD50 was 1.7 x 10(2) sporozoites. Oocyst production was also dependent on inoculum size. Oocysts harvested from embryos sporulated. The oocysts were inoculated into 13-day-old chickens, and oocysts, capable of sporulating normally, were recovered from ceca 7 days after inoculation.

Eimeria tenella: growth and drug sensitivity in tissue culture under reduced oxygen

For Plasmodium falciparum in culture, growth is enhanced as oxygen tension is lowered and drug susceptibility, particularly susceptibility to 70S ribosomal and mitochondrial inhibitors, changes. Whether similar effects occur in Eimeria tenella was tested as a possible explanation for why certain 70S ribosomal inhibitors, while active in Eimeria-infected birds, are virtually inactive in vitro under ambient oxygen conditions. It was reasoned that perhaps these agents would exhibit good in vitro potency under reduced oxygen conditions. Such proved not to be the case, and it was further found that no positive effect on Eimeria growth occurred under these conditions. Finally, lowering oxygen tension had no substantial effects on sensitivity to anticoccidials or mitochondrial inhibitors.

Research note: immunity to Eimeria in broilers reared on nicarbazin and salinomycin

The incidence of oocysts was monitored in the litter at two broiler farms where birds were reared to 8 wk of age using a shuttle program involving nicarbazin (from 0 to 21 days of age) and salinomycin (from 21 to 44 days of age). Some birds from these farms were challenged with three species of Eimeria to see whether immunity had developed as a result of prior exposure to infection. Oocysts of at least three species of Eimeria were present in small numbers in the litter. Birds from both farms were immune to Eimeria acervulina and Eimeria maxima (judged by weight gain) although the immunity was incomplete as evidenced by oocyst production. Birds from one farm were immune to Eimeria tenella (judged by weight gain) but birds from the other farm were susceptible to this species.

Distribution of oocysts, sporocysts and sporozoites of Eimeria tenella and Eimeria maxima in the digestive tract of chicken

The distribution of oocysts, sporocysts and sporozoites of Eimeria tenella and Eimeria maxima in the digestive tract of chicken and in excreta was investigated. At 1 h after the oral inoculation of E. tenella oocysts, the number of sporocysts in the cecum was 3.4 x 10(6) and decreased gradually thereafter, and the number of sporozoites in the cecum increased and remained at a high level until 12 h after the inoculation. Small numbers of sporocysts and sporozoites of E. tenella were found in other intestinal sites. A great number of E. maxima sporozoites was found, especially in the jejunum, 2 h after the inoculation. The findings that the largest populations of sporozoites of E. tenella and E. maxima were found in the cecum and the jejunum, respectively, indicate that the site specificity of sporozoite invasion for each species is determined before the invasion takes place.

Influence of coccidiosis on Salmonella colonization in broiler chickens under floor-pen conditions

The influence of coccidiosis on colonization of Salmonella typhimurium in broiler chickens under floor pen conditions was studied by semiquantitative methods. Chickens of two groups, unmedicated and medicated with nicarbazin (125 ppm via the feed), were exposed to three species of Eimeria (Eimeria tenella, Eimeria maxima, and Eimeria acervulina) at 2, 3, and 4 wk of age and given S. typhimurium in the feed 2 days later. Salmonella typhimurium was isolated most often (100%) from ceca of chickens exposed at 3 wk of age. Birds in the unmedicated group were positive for S. typhimurium at a higher rate than those in the medicated group. Salmonella typhimurium was detected in livers only in a few unmedicated birds.

Simultaneous purification of merozoites and schizonts of Eimeria tenella (Apicomplexa) by Percoll flotation and assessment of cell viability with a double fluorescent dye assay

The asynchronous development of Eimeria tenella in orally infected chickens makes it possible to purify second generation merozoites (meros) and shizonts from a single mucosal homogenate. After centrifugation in 30% Percoll in phosphate-buffered saline (Percoll-PBS), debris, villi, and schizonts float, whereas meros and erythrocytes are pelleted. Erythrocytes are lysed by a mild hypotonic shock; meros are filtered through a cotton wool plug and collected by centrifugation. The 30% Percoll-PBS supernatant fraction is diluted to 25% Percoll-PBS and centrifuged to sediment mature schizonts. By repeated slow-speed centrifugation, schizonts are separated from nuclei and small-sized debris. In less than 3 hr, 8.8 +/- 2.3 x 10(8) meros and 7.2 +/- 3.9 x 10(6) schizonts are collected from 10 infected chickens. Contamination with host material is 2% for meros but variable for schizonts. For the assessment of cell viability, ethidium bromide (EB) and acridine orange (AO) have been used as markers for dead and living cells, respectively, in a single step method. More than 95% of the schizonts and meros accumulate AO and no EB, whereas lysed erythrocytes and all cells hosting a schizont are permeable to EB. After incubation of meros and schizonts in synthetic media with [5,6- 3H]uracil, label accumulates in the perchloric acid-soluble and -insoluble fractions, indicating transport, salvage, and incorporation of the pyrimidine precursor in nucleic acids. If stored on ice, meros and schizonts retain metabolic activity for at least 5 hr, but metabolism declines rapidly during incubation at 41 C.

X-irradiation of Eimeria tenella oocysts provides direct evidence that sporozoite invasion and early schizont development induce a protective immune response(s)

Sporulated oocysts of the protozoan parasite Eimeria tenella were attenuated by exposure to various doses of X-radiation to inhibit intracellular replication and thus determine whether sporozoites alone can induce a protective immune response. Exposure to doses greater than 15-kilorads had a significant effect on development, as indicated by the absence of oocyst production in chickens infected with parasites treated with 20 or 30 kilorads of radiation. Infection with nonirradiated or 15-kilorad-exposed parasites led to either normal or reduced oocyst shedding. Equivalent protection was afforded chickens inoculated with a minimum immunizing dose of either nonirradiated or 20-kilorad-irradiated E. tenella oocysts. Immunofluorescence staining of cecal tissue from chickens inoculated with 10(7) nonirradiated or 20- or 30-kilorad-irradiated oocysts with stage-specific monoclonal antibodies showed no significant difference in sporozoite invasion between treatment groups. Normal merogonic development was observed at appropriate times (48, 60, 72, and 96 h) postinfection in chickens inoculated with nonirradiated oocysts. In contrast, irradiated parasites exhibited minimal merogonic development at 48 h postinfection. Furthermore, no merogonic stages were observed at times of otherwise peak merozoite development (60, 72, and 96 h) in cecal tissue from chickens inoculated with irradiated parasites. Infection of chicken cells with irradiated or nonirradiated parasites in vitro corroborated these findings and indicate that events early after sporozoite invasion induce a protective immune response against this parasite.