Immunity to Eimeria infections

Temporal changes of genes associated with intestinal homeostasis in broiler chickens following a single infection with Eimeria acervulina

Infection with the protozoan parasite Eimeria can cause the economically devastating disease coccidiosis, which is characterized by gross tissue damage and inflammation resulting in blunted villi and altered intestinal homeostasis. Male broiler chickens at 21 d of age were given a single challenge with Eimeria acervulina. Temporal changes in intestinal morphology and gene expression were investigated at 0, 3, 5, 7, 10, and 14 d postinfection (dpi). There were increased crypt depths for chickens infected with E. acervulina starting at 3 dpi and continuing to 14 dpi. At 5 and 7 dpi, infected chickens had decreased Mucin2 (Muc2), and Avian beta defensin (AvBD) 6 mRNA at 5 and 7 dpi and decreased AvBD10 mRNA at 7 dpi compared to uninfected chickens. Liver-enriched antimicrobial peptide 2 (LEAP2) mRNA was decreased at 3, 5, 7, and 14 dpi compared to uninfected chickens. After 7 dpi, there was increased Collagen 3a1 and Notch 1 mRNA compared to uninfected chickens. Marker of proliferation Ki67 mRNA was increased in infected chickens from 3 to 10 dpi. In addition, the presence of E. acervulina was visualized by in situ hybridization (ISH) with an E. acervulina sporozoite surface antigen (Ea-SAG) probe. In E. acervulina infected chickens, Ea-SAG mRNA was only detectable on 5 and 7 dpi by both ISH and qPCR. To further investigate the site of E. acervulina infection, Ea-SAG and Muc2 probes were examined on serial sections. The Muc2 ISH signal was decreased in regions where the Ea-SAG ISH signal was present, suggesting that the decrease in Muc2 by qPCR may be caused by the loss of Muc2 in the localized regions where the E. acervulina had invaded the tissue. Eimeria acervulina appears to manipulate host cells by decreasing their defensive capabilities and thereby allows the infection to propagate freely. Following infection, the intestinal cells upregulate genes that may support regeneration of damaged intestinal tissue.

Dietary supplementation of sulfur amino acids improves intestinal immunity to Eimeria in broilers treated with anti-interleukin-10 antibody

Oral antibody to interleukin-10 (anti-IL-10) enhances the intestinal immune defense against Eimeria. The sulfur amino acids methionine and cysteine (M+C) play essential roles in inducing and maintaining protective immune responses during intestinal infections. Hence, increased dietary M+C may support the anti-IL-10-induced intestinal immunity to Eimeria. Broilers (n = 640) were arranged in a 2 × 2 × 2 factorial design with 2 levels of each of the 3 main factors: dietary standardized ileal digestible (SID) M+C levels (0.6% or 0.8%), dietary anti-IL-10 supplementation (with or without), and coccidiosis challenge (control or challenge). Briefly, the broilers were supplied with either 0.6% or 0.8% SID M+C, each with or without anti-IL-10 (300 μg/kg), from d 10 to 21. On d 14, broilers from each diet were gavaged with either PBS or Eimeria. The resulting Eimeria infection induced fecal oocyst shedding and intestinal lesions. Broilers fed 0.8% SID M+C (main effects, P ≤ 0.05) had decreased feed-to-gain ratio, increased duodenum and cecum luminal anti-Eimeria IgA titers, and decreased fecal oocyst counts, when compared to 0.6% SID M+C. The supplementation of anti-IL-10 (main effects, P ≤ 0.05) increased cecum luminal total IgA concentration and decreased cecum lesions. Interactions (P ≤ 0.05) were detected for growth performance and cecum luminal IFN-γ. Briefly, the highest body weight gain and feed intake were reached in PBS-gavaged broilers fed 0.8% SID M+C with no anti-IL-10 and in Eimeria-challenged broilers fed 0.8% SID M+C with anti-IL-10. In Eimeria-infected broilers, anti-IL-10 increased intestinal luminal IFN-γ and body weight gain only at 0.8% SID M+C. Collectively, anti-IL-10 increased intestinal luminal IFN-γ levels, decreased cecum lesions and restored growth only when fed with adequate amounts of sulfur amino acids. Our findings underscore the importance of providing sufficient essential nutrients to support the anti-IL-10 induced immunity against coccidiosis.

Eimeria infections in domestic and wild ruminants with reference to control options in domestic ruminants

Eimeria infections are commonly seen in a variety of mammalian hosts. This genus of unicellular sporozoan parasites causes significant disease (coccidiosis) in different livestock species leading to economic losses for agricultural producers. Especially the production of cattle, sheep, and goat is strongly dependent on efficient coccidiosis control. However, many other livestock hosts like, e.g., camelids, bison, rabbits, and guinea pigs may benefit from reduced parasite transmission and targeted control measures as well. Besides livestock, also wildlife and pet animals may be affected by Eimeria infections resulting in clinical or subclinical coccidiosis. Wildlife herd health is crucial to conservation efforts, and Eimeria species are a prevalent pathogen in multiple mammalian wildlife species. This review aims to highlight the epidemiology of mammalian Eimeria infections in both wild and domestic ruminants, including host specificity, transmission, survival of environmental oocysts, occurrence, and risk factors for infection. Understanding general drivers of Eimeria infection may support adequate livestock and wildlife management. Furthermore, control options for livestock with reference to management factors, drug application, and alternative approaches are discussed. The goal of Eimeria control should be to reduce pathogen transmission in different host species and to improve sustainable livestock production. Controlling Eimeria infections in livestock is important considering both their animal welfare impact and their high economic relevance.

Starving for nutrients: anorexia during infection with parasites in broilers is affected by diet composition

In 2 experiments, we investigated whether diet composition plays a role in pathogen-induced anorexia, the voluntary reduction in ADFI during infection in broilers. We hypothesized that either energy or CP dietary content could influence the extent of anorexia in Ross 308 broilers and infection outcomes with Eimeria maxima. From d 13 of age, half of the birds were infected, and half were uninfected. ADFI was measured daily, and BW every 3 d until d 29. Oocyst excretion was measured daily from d 17 to 23. The impact of parasitism on the small intestine was assessed on d 19 and 25. In Experiment 1, 336 birds were offered diets progressively diluted with lignocellulose, starting from a diet with 3,105 (kcal ME/kg) and 20% CP. There was a significant interaction between infection and diet on ADFI during the acute stage of infection (d 17 to 21): for control birds diet dilution decreased ADFI and consequently reduced energy and CP intake. For infected birds, diet dilution increased ADFI, leading to the same energy and CP intake across diets. Oocyst excretion and villi length to crypt depth ratio (VCR) were constant across infected treatments. In Experiment 2, 432 birds were offered diets with constant ME (3,105 kcal/kg), but different CP contents (24, 20, 26, and 12%). Infection significantly reduced ADFI. Although there was no interaction between infection and diet on ADFI, there was an interaction on CP intake during the acute stage of infection. Infected birds on the 20% CP diet achieved the same CP intake as uninfected birds. There were no differences in the VCR and ADG of the infected birds on 24, 20 and 16% CP treatments, but birds on 12% had the lowest ADG and excreted more oocysts. We suggest that during infection, birds target a nutrient resource intake, which appears to be beneficial for infection outcomes, while at the same time they avoid excess protein intake. We conclude that different mechanisms regulate ADFI in infected and uninfected birds.

Immunotherapy With Egg Yolk Eimeria sp.-Specific Immunoglobulins in SPF Leghorn Chicks Elicits Successful Protection Against Eimeria tenella Infection

Avian coccidiosis is the first to most economically important parasite disease affecting poultry industries worldwide. Current prevention measures are largely based upon prophylactic chemotherapy supplemented by the application of live attenuated or wild-type parasite vaccines. However, the rising appearance of drug resistance, consumer's concern for antibiotics use in poultry production and higher manufacturing cost of live vaccines has driven to adopt new technologies aimed at increasing animal health and production efficiency. Supplementing chickens with egg yolk Eimeria sp.-specific immunoglobulins can be a viable alternative to avoid severe outbreaks of the disease. Twelve-week-old SPF White Leghorn chickens were experimentally infected with a large dose of E. tenella. During the prepatent period, the birds were supplemented by oral gavage with 60 or 120 mg/bird of hyperimmune egg yolk Eimeria species-specific immunoglobulins Y (Supracox®, SC) on a daily basis. The animals were euthanized 7 days post-infection (PI) and their passive immune protection was evaluated. Birds treated with 120 mg/bird of SC showed more viability, increased body weight gain (BWG), a normal hematocrit level (HCT), reduced oocyst output per gram of feces (OPG) or cecal tissue (OPGC), and fewer cecal lesions compared to the untreated infected (UI) control group. Birds supplemented with 60 mg/bird of SC did not show any significant difference on BWG, HCT, OPG, OPGC, and cecal lesion score when compared with the UI group. An ELISA test of the SC showed a weak cross-reactivity of IgY toward two asexual zoite stages of E. tenella. Western blot analysis of the sporozoite with SC showed few antigens barely recognized, while more stained bands were detected in the merozoite (≈82, ≈60, ≈54, ≈40, ≈38, ≈27.5, and ≈13 kDa). Oral immunotherapy using egg yolk polyclonal IgYs against Eimeria sp. represents an effective and natural resource against severe E. tenella infection favoring the gradual withdrawal of the anticoccidial drugs and antibiotics.

Poultry Coccidiosis: Design and Interpretation of Vaccine Studies

Eimeria infection impacts upon chicken welfare and economic productivity of the poultry sector. Live coccidiosis vaccines for chickens have been available for almost 70 years, but the requirement to formulate blends of oocysts from multiple Eimeria species makes vaccine production costly and logistically demanding. A multivalent vaccine that does not require chickens for its production and can induce protection against multiple Eimeria species is highly desirable. However, despite the identification and testing of many vaccine candidate antigens, no recombinant coccidiosis vaccine has been developed commercially. Currently, assessment of vaccine efficacy against Eimeria, and the disease coccidiosis, can be done only through in vivo vaccination and challenge experiments but the design of such studies has been highly variable. Lack of a "standard" protocol for assessing vaccine efficacy makes comparative evaluations very difficult, complicating vaccine development, and validation. The formulation and schedule of vaccination, the breed of chicken and choice of husbandry system, the species, strain, magnitude, and timing of delivery of the parasite challenge, and the parameters used to assess vaccine efficacy all influence the outcomes of experimental trials. In natural Eimeria infections, the induction of strong cell mediated immune responses are central to the development of protective immunity against coccidiosis. Antibodies are generally regarded to be of lesser importance. Unfortunately, there are no specific immunological assays that can accurately predict how well a vaccine will protect against coccidiosis (i.e., no "correlates of protection"). Thus, experimental vaccine studies rely on assessing a variety of post-challenge parameters, including assessment of pathognomonic lesions, measurements of parasite replication such as oocyst output or quantification of Eimeria genomes, and/or measurements of productivity such as body weight gain and feed conversion rates. Understanding immune responses to primary and secondary infection can inform on the most appropriate immunological assays. The discovery of new antigens for different Eimeria species and the development of new methods of vaccine antigen delivery necessitates a more considered approach to assessment of novel vaccines with robust, repeatable study design. Careful consideration of performance and welfare factors that are genuinely relevant to chicken producers and vaccine manufacturers is essential.

Antibody and cytokine response to Cystoisospora suis infections in immune-competent young pigs

Background

To date, investigations on the immune response to Cystoisospora suis infections focused on suckling piglets, the age group clinically most affected. Actively immunizing piglets is unfeasible due to their immature immune system and the typically early infection in the first days after birth. Therefore, understanding and possibly enhancing the immune response of immune-competent animals is the prerequisite to develop a passive immunization strategy for piglets which currently rely on very limited treatment options.

Methods

To investigate antibody and cytokine responses of immune-competent animals and the impact of the oral immunization protocol on their immune response, growers with unknown previous exposure to C. suis (10–11 weeks-old) were infected one or three times with different doses (600 and 6000 or 200 and 2000, respectively) of C. suis oocysts, and compared to uninfected controls. Oocyst excretion was evaluated, and blood and intestinal mucus antibody titers were determined by IFAT. Systemic production of Th1, Th2, inflammatory and regulatory cytokines was determined in different immune compartments at mRNA and (after stimulation with a recombinant merozoite-protein) at protein level by PCR and multiplex fluorescent immunoassay, respectively.

Results

Infection generated significantly increased serum IgA and IgG levels against C. suis sporozoites and merozoites, irrespective of infection mode, with IgG against merozoites showing the strongest increase. No clinical signs and only occasional excretion were observed. The systemic cytokine response to C. suis was only weak. Nonetheless, in white blood cells, IL-4, IL-6 and IL-10 mRNA-levels significantly increased after infection, whereas IFN-ɣ, IL-2 and TGF-β expression tended to decrease. In mesenteric lymph nodes (MLN), IL-10 and TNF-α levels were elevated while splenic cytokine expression was unaltered upon infection. Stimulated MLN-derived lymphocytes from infected pigs produced slightly more IL-12 and less IFN-α than controls.

Conclusions

An infection and a subsequent systemic immune response can be induced in immune-competent animals by all evaluated infection models and growers can be used as models to mimic sow immunizations. The immune response to C. suis, although mild and with considerable variation in cytokine expression, was characterized by a Th2-associated and regulatory cytokine profile and antibody production. However, none of the parameters clearly stood out as a potential marker associated with protection. Antibody titers were significantly positively related with oocyst excretion and might thus serve as correlates for parasite replication or severity of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2974-6) contains supplementary material, which is available to authorized users.

Experimental Toxoplasma gondii and Eimeria tenella co-infection in chickens

The widespread apicomplexan parasites Toxoplasma gondii (T. gondii) and Eimeria tenella (E. tenella) are important pathogens with high prevalence in poultry. The aim of our study was the investigation of mutual influences in co-infected chickens, focusing on immune response and course of infection. Two separate trials were performed using in total 96 1-day-old chickens, divided into four study groups: group NC (negative control, uninfected), group PC-T (oral or intramuscular infection with T. gondii oocysts (trial 1) or tachyzoites (trial 2), respectively), group PC-E (oral infection with E. tenella (trial 1) or E. tenella and Eimeria acervulina (trial 2)), and group TE (co-infection). T. gondii and Eimeria infections were validated by different parameters, and cytokine expression in the gut and spleen was investigated. T. gondii-specific antibodies were detected earliest 4 days post infection (p.i.) by immunoblot and direct DNA detection was possible in 22.1% of all tissue samples from infected chickens. Eimeria spp. merogony seemed to be enhanced by co-infection with T. gondii, interestingly without marked differences in oocyst excretion between co-infected and Eimeria spp. mono-infected chickens. An increase of messenger RNA (mRNA) expression of Th1- (IFN-γ, IL-12, TNF-α) and Th2-related cytokines (IL-10) mainly in groups PC-E and TE was observed, however, without statistically significant differences between co-infection and single infection with Eimeria. In conclusion, most of the measurable immune response could be attributed to Eimeria infection. To the best of our knowledge, this is the first report on co-infection experiments of T. gondii with Eimeria spp. in chickens.

Live Eimeria vaccination success in the face of artificial non-uniform vaccine administration in conventionally reared pullets

Live Eimeria vaccines against coccidiosis in poultry initiate immunity using a vaccine dose containing few oocysts; protection is enhanced through subsequent faecal-oral transmission ("cycling") of parasites in the poultry house. Spray-administered Eimeria vaccines can permit wide variations in doses ingested by individual chicks; some chicks may receive no primary vaccination at all. Consequently, protective immunity for the entire flock depends on successful environmental cycling of vaccine progeny. Pullets missing primary vaccination at day of age can become protected from coccidial challenge through cycling of vaccine progeny oocysts from vaccinated (V) cage mates. This study tested whether 40% cage floor coverage (CFC) with a durable material could improve protection against challenge in these "contact-vaccinated" (CV) or successfully V pullets. The six treatment groups tested were CV, V or sham-vaccinated pullets cage-reared on either 0% or 40% CFC. Oocyst output was measured separately for each group for 30 days following vaccine administration. Lesion scores, body weights and total oocyst outputs were measured to quantify protection at 30 days of age against single or mixed Eimeria species challenge infections. Use of 40% CFC to promote low-level oocyst cycling impacted the flock in two ways: (1) more uniform flock immunity was achieved in the 40% CFC (CV similar to V pullets) compared with 0% CFC and (2) protection was enhanced in the 40% CFC compared with the 0% CFC. The use of CFC is an easily adopted means of improving live Eimeria vaccination of caged pullets.

Parasite infection negatively affects PHA-triggered inflammation in the subterranean rodent Ctenomys talarum

Magnitude and effectiveness of immune responses vary greatly between and within species. Among factors reported to determine this variation, parasitism is a critical one, although controversial effects of parasites over immunological indices have been reported. Information regarding immune strategies in species with different life histories is crucial to better understand the role of immune defenses in an ecological and evolutionary context. Here, we examine the influence of the parasite community on immune responsiveness of a solitary subterranean rodent, Ctenomys talarum. To do this, we assessed the impact of the natural parasite community and the experimental infection with Eimeria sp. on the phytohemagglutinin (PHA)-response, as well as other immune, condition, nutrition, and stress parameters. PHA-triggered inflammation was similarly impaired by Eimeria sp. infection alone or co-occurring with a number of gastrointestinal nematodes. None of the other physiological parameters studied were affected by parasitism. This indicates that parasitism is a general key factor modulating immune responsiveness of the host, and in particular for C. talarum, it could explain the great inter-individual variation previously observed in the PHA-response. Thus, our results highlight the importance of taking the parasite community into account in ecoimmunological studies, particularly when using immunological indices.

Seasonal impact on the prevalence of coccidian infection in broiler chicks across poultry farms in the Kashmir valley

The information on the epidemiology and control of coccidian parasites of broilers in Kashmir valley is based on the reports available from other regions of the world. With this background, the present study was conducted to investigate the seasonal prevalence of the disease in the temperate agro-climatic conditions of Kashmir valley. A standard protocol for sampling was followed according to which five birds per 10,000 is sufficient to diagnose coccidiosis. Microscopic examination (under 10× and 40× objective lens) was used to reveal the presence of coccidial oocysts. Different species of genus Eimeria were identified on the basis of their predilection site, morphology and size. Coccidiosis was most prevalent in autumn 45.12 ± 2.55 (September 47.5 %, October 42.42 % and November 45.46 %) followed by summer 30.84 ± 6.86, spring 23.81 ± 2.81 and winter 20.29 ± 6.40. In summer, prevalence of disease was low but afterwards prevalence of disease rose up from August to October. In spite of high relative humidity in winter, disease showed low prevalence rate. Over all prevalence for the whole year was 29.87 %. Among species Eimeria tenella was the most dominant parasite showing highest prevalence of 18.13 %. Variation in incidence of coccidiosis with respect to seasons showed a strong correlation and data was found to be statistically significant with P < 0.05. The results obtained would be quite useful to devise appropriate and effective control strategies and prophylactic programs for coccidiosis in poultry unique to this climatic zone and other parts of the world with similar climatic and poultry production systems.

Poultry coccidiosis: recent advancements in control measures and vaccine development

Coccidiosis is recognized as the major parasitic disease of poultry and is caused by the apicomplexan protozoan Eimeria. Coccidiosis seriously impairs the growth and feed utilization of infected animals resulting in loss of productivity. Conventional disease control strategies rely heavily on chemoprophylaxis and, to a certain extent, live vaccines. Combined, these factors inflict tremendous economic losses to the world poultry industry in excess of USD 3 billion annually. Increasing regulations and bans on the use of anticoccidial drugs coupled with the associated costs in developing new drugs and live vaccines increases the need for the development of novel approaches and alternative control strategies for coccidiosis. This paper aims to review the current progress in understanding the host immune response to Eimeria and discuss current and potential strategies being developed for coccidiosis control in poultry.

Differing susceptibilities of Eimeria acervulina, Eimeria maxima, and Eimeria tenella oocysts to desiccation

Outbreaks of avian coccidiosis may occur when susceptible chickens are raised on litter containing viable Eimeria oocysts. The purpose of this study was to compare the relative sensitivities of Eimeria acervulina, Eimeria maxima, and Eimeria tenella oocysts to dessication. Sporulated E. acervulina, E. maxima, or E. tenella oocysts were incorporated into gelatin beads and incubated at 32 C for 0, 1, 2, or 3 days. In vitro oocyst excystation rates were measured for each combination of Eimeria species and incubation time. Day-old broiler chicks were allowed to ingest the oocysts-containing beads, and total oocyst production was measured from days 5-8 post-inoculation. Although no effect on excystation was observed, E. maxima oocysts displayed greater resistance to drying compared to E. acervulina and E. tenella oocysts. Eimeria acervulina oocyst production decreased 100-fold after 1-2 days incubation. Eimeria tenella oocysts were slightly more resistant to drying in that a 100-fold decrease in oocyst production was delayed until 2 days. For both E. acervulina and E. tenella , very few oocysts were observed after 3 days incubation. Eimeria maxima oocyst production remained high at all time points. Subsequent studies revealed E. maxima oocyst production was ablated only after 5 days incubation. These findings may explain in part the observed prevalence of E. maxima in litter from commercial poultry operations.

Isolation of an Eimeria ninakohlyakimovae field strain (Canary Islands) and analysis of its infection characteristics in goat kids

The current study was conducted to isolate a field strain of Eimeria ninakohlyakimovae, characterize its infectivity and the response to challenge under experimental conditions. The isolated strain (GC) induced a prepatent period of 14-15 days p.i., a patency of 7±2 days and a noticeable pathogenicity in infected goat kids. Challenge trials resulting in a decrease of oocysts per gram counts as well as a milder intensity of clinical signs in re-infected animals indicated the capacity of this strain to induce protective immune response. Altogether, the data reported in the present study suggest that the strain E. ninakohlyakimovae GC is a useful tool for the investigation of mechanisms of pathogenicity as well as host protective immune response in caprine coccidiosis, representing a valuable prerequisite for the development of future strategies in prophylaxis and control of this important parasitic disease in goat.

Gel-Bead Delivery of Eimeria oocysts protects chickens against coccidiosis

Vaccines composed of either virulent or attenuated Eimeria spp. oocysts have been developed as an alternative to medication of feed with ionophore drugs or synthetic chemicals. The purpose of this study was to evaluate the use of gel-beads containing a mixture of Eimeria acervulina, Eimeria maxima, and Eimeria tenella oocysts as a vaccine against coccidiosis. Newly hatched chicks (Gallus gallus domesticus) were either sprayed with an aqueous suspension of Eimeria oocysts or were allowed to ingest feed containing Eimeria oocysts-incorporated gel-beads. Control day-old chicks were given an equivalent number of Eimeria oocysts (10(4) total) by oral gavage. After 3 days, chicks were randomly assigned to individual cages, and feces were collected between days 5 and 8 postinfection. All samples were processed for total Eimeria oocysts. At 4 wk of age, all chickens and a control nonimmunized group received a high-dose E acervulina, E maxima, and E. tenella challenge infection. Oocyst excretion by chicks fed gel-beads or inoculated by oral gavage was 10- to 100-fold greater than that of chicks spray-vaccinated with the Eimeria oocysts mixture (log 6.3-6.6 vs. log 4.8). Subsequent protection against challenge as measured by weight gain and feed conversion efficiency was significantly greater (P < 0.05) in gel-bead and oral gavage groups compared with spray-vaccinated or nonimmunized groups. Also, gel-bead and oral gavage groups showed no significant difference (P > 0.05) in weight gain and feed conversion efficiency compared with nonchallenged controls. These findings indicate that incorporation of Eimeria spp. oocysts in gel-beads may represent an effective way to deliver live oocyst vaccines to day-old chicks for preventing subsequent outbreaks of coccidiosis in the field.

Induction of protective immunity against Eimeria tenella, Eimeria maxima, and Eimeria acervulina infections using dendritic cell-derived exosomes

This study describes a novel immunization strategy against avian coccidiosis using exosomes derived from Eimeria parasite antigen (Ag)-loaded dendritic cells (DCs). Chicken intestinal DCs were isolated and pulsed in vitro with a mixture of sporozoite-extracted Ags from Eimeria tenella, E. maxima, and E. acervulina, and the cell-derived exosomes were isolated. Chickens were nonimmunized or immunized intramuscularly with exosomes and subsequently noninfected or coinfected with E. tenella, E. maxima, and E. acervulina oocysts. Immune parameters compared among the nonimmunized/noninfected, nonimmunized/infected, and immunized/infected groups were the numbers of cells secreting T(h)1 cytokines, T(h)2 cytokines, interleukin-16 (IL-16), and Ag-reactive antibodies in vitro and in vivo readouts of protective immunity against Eimeria infection. Cecal tonsils, Peyer's patches, and spleens of immunized and infected chickens had increased numbers of cells secreting the IL-16 and the T(h)1 cytokines IL-2 and gamma interferon, greater Ag-stimulated proliferative responses, and higher numbers of Ag-reactive IgG- and IgA-producing cells following in vitro stimulation with the sporozoite Ags compared with the nonimmunized/noninfected and nonimmunized/infected controls. In contrast, the numbers of cells secreting the T(h)2 cytokines IL-4 and IL-10 were diminished in immunized and infected chickens compared with the nonimmunized/noninfected and the nonimmunized/infected controls. Chickens immunized with Ag-loaded exosomes and infected in vivo with Eimeria oocysts had increased body weight gains, reduced feed conversion ratios, diminished fecal oocyst shedding, lessened intestinal lesion scores, and reduced mortality compared with the nonimmunized/infected controls. These results suggest that successful field vaccination against avian coccidiosis using exosomes derived from DCs incubated with Ags isolated from Eimeria species may be possible.

Effect of Eimeria acervulina infection history on the immune response and transmission in broilers

Heterogeneity in exposure to Eimeria spp. of chickens in a flock will result in differences between individual birds in oocyst output and acquired immunity, which subsequently affects transmission of the parasite in the population. The aim of this study was to quantify effects of previous infection of broilers with Eimeria acervulina on immune responses, oocyst output and transmission. A transmission experiment was carried out with pair-wise housed broilers, that differed in infection history. This "infection history" was achieved by establishment of a primary infection by inoculation of birds with 50,000 sporulated E. acervulina oocysts at day 6 of age ("primed"); the other birds did not receive a primary infection ("naïve"). The actual transmission experiment started at day 24 of age: one bird (I) was inoculated with 50,000 sporulated oocysts and was housed together with a non-inoculated contact bird (C). Oocyst excretion and parameters describing transmission, i.e. the number of infected C birds and time passed before start of excretion of C birds, were determined from day 28 to day 50 for six pairs of four different combinations of I and C birds (I-C): naïve-naïve, naïve-primed, primed-naïve and primed-primed. Immune parameters, CD4(+), CD8(+), αβTCR(+) and γδTCR(+) T cells and macrophages in duodenum, were determined in an additional 25 non-primed, non-inoculated control birds, and in the naïve-naïve and naïve-primed groups, each group consisting of 25 pairs. Although the numbers of CD4(+) T cells and γδTCR(+) T cells increased after primary infection, none of the immunological cell types provided an indication of differences in infectivity, susceptibility or transmission between birds. Oocyst output was significantly reduced in primed I and C birds. Transmission was reduced most in the primed-primed group, but nonetheless transmission occurred in all groups. This study also showed that acquired immunity significantly reduced oocyst output after inoculation and contact-infection, but not sufficiently to prevent transmission to contact-exposed birds.

T cell reactions of Eimeria bovis primary and challenge-infected calves

Eimeria bovis infections commonly have clinical impact only on young animals, as homologous reinfections generally are under immunological control. So far, the nature of the immune responses delivering protection to calves has not been investigated. In this study we therefore analysed local and peripheral proliferative T cell activities of primary and challenge-infected calves and investigated the occurrence of T cell phenotypes in the peripheral blood and in mucosal gut segments isolated either by bioptic means or by necropsies.We show that lymphocytes of E. bovis-infected calves exhibit effective, transient antigen-specific proliferative responses in the course of prepatency of primary infection but fail to react after homologous reinfection suggesting early abrogation of parasite development. Whilst in primary infection an expansion of peripheral CD4+ T cells was observed, reinfection had no effect on the proportions of CD4+, CD8+ subsets or gammadeltaTCR+ T cells. In contrast, both E. bovis primary and challenge infections had an impact on local tissue T cell distribution. Primary infection was characterised by a CD4+ T cell infiltration early in prepatency in ileum and later in colon mucosa, whereas CD8+ T cells were only found accumulating in the latter gut segment. Challenge infection led to infiltration of both CD4+ and CD8+ T cells in small intestine and large intestine segments indicating protective functions of both cell types. In contrast, infiltration of ileum and colon mucosa with gammadeltaTCR+ T cells was restricted to primary infection.

Cross-reactivity among antisera raised against five avian Eimeria species in the natural host and in rabbits

Water- and SDS-soluble antigens were prepared from purified sporulated oocysts of Eimeria acervulina, E. maxima, E. necatrix, E. praecox and E. tenella. Reactivity of . chicken hyperimmune anti-Eimeria sera, rabbit anti-oocyst and rabbit anti-sporozoite sera with the homologous and heterologous oocyst antigens were determined and cross-reactivities were expressed as a percentage of those homologous sera. The results demonstrated that the antisera from chickens infected naturally with Eimeria species differed in their reactivities from those of the rabbit antisera. Occurrence of a high level cross-reactivity among the chicken antisera may suggest that the development of parasites inside the host cells, or the production of substances during the life-cycle, affect the extent of immune responses and that most non-protective antibodies are cross-reactive.

Field application of a subunit vaccine against an enteric protozoan disease

Background

Coccidiosis is a major global veterinary health problem in intensively reared chickens. It is caused by apicomplexan parasites of the genus Eimeria.

Principal Findings

A subunit vaccine composed of purified antigens from the gametocytes of Eimeria maxima was used to stimulate the production and transfer of maternal antibodies between breeding hens and their hatchlings. The vaccine was injected into hens twice before they began laying eggs. Immunization had no adverse affects on egg laying or health of the hens and resulted in high antibody levels throughout the life of the hens. Progeny of immunized hens excreted significantly less oocysts of various species of Eimeria in their faeces than chicks from unvaccinated hens. Furthermore, the offspring of vaccinated hens developed stronger natural immunity to Eimeria, so that they were resistant to challenge infection even at 8 weeks of age, well after all maternal antibodies had left their circulation. Field trials were conducted in South Africa, Brazil and Thailand, involving at least 1 million progeny of vaccinated hens and at least 1 million positive control birds (raised on feed containing anticoccidial drugs or immunized with a live vaccine) in each country. Additionally, trials were carried out in Israel involving 60 million progeny of vaccinated hens and 112 million positive control birds. There were no significant differences in growth rate, feed conversion ratios or mortality in the offspring of vaccinated hens compared with the positive control chickens in any of these countries regardless of different management practices, different breeds of chickens or climate.

Conclusions

These results demonstrate that a vaccine composed of antigens purified from the gametocytes of Eimeria can be used safely and effectively to prevent the deleterious effects of coccidiosis. It is the first subunit vaccine against any protozoan parasite to be successfully applied on a commercial scale.

Endogenous development, pathogenicity and host specificity of Eimeria cahirinensis Couch, Blaustein, Duszynski, Shenbrot and Nevo, 1997 (Apicomplexa: Eimeriidae) from Acomys dimidiatus (Cretzschmar 1826) (Rodentia: Muridae) from the Near East

Eimeria cahirinensis Couch et al. 1997 was found in faecal samples of Acomys dimidiatus from three different localities in the Near East. Twenty-two of 104 (21%) A. dimidiatus trapped on both the south- and north-facing slopes of "Evolution Canyon", Lower Nahal Oren, Mt. Carmel, Israel in August 2001 and 2002 were infected with E. cahirinensis. Oocysts were also obtained from a single individual of A. dimidiatus trapped in Wadi Ramm, Jordan in the summer of 1999. Laboratory-reared spiny mice (Acomys spp.) were inoculated to determine the prepatent and patent period, sporulation time, site of infection, immunogenicity, pathogenicity, pathology and morphology of endogenous stages of E. cahirinensis. Both asexual and sexual stages were localised in the apical part of duodenal and jejunal villi. An experimental inoculation of representatives of several rodent genera revealed the host range of E. cahirinensis to be limited to the genus Acomys.

Eimeria tenella: B-cell epitope mapping following primary and secondary infections

Immunisation against coccidiosis has become more reliable and effective with improved administration techniques for new vaccines. On the other hand, an ideal coccidial vaccine should contain both B- and T-cell immunogenic epitopes. Fine specificity of B-cell epitopes recognised by antibodies prepared following primary and secondary infections with Eimeria tenella were studied using "PepScan" techniques. Mapping of B-cell epitopes within an antigenic sequence from E. tenella showed that four distinct types of epitopes were recognised by the host immune system during the primary and secondary infections with the parasite. These observations demonstrated that new epitopes are also involved in induction of antibody responses following the secondary infection.

Recent advances in immunomodulation and vaccination strategies against coccidiosis

Coccidiosis is a ubiquitous intestinal protozoan infection of poultry seriously impairing the growth and feed utilization of infected animals. Conventional disease control strategies rely heavily on chemoprophylaxis, which is a tremendous cost to the industry. Existing vaccines consist of live virulent or attenuated Eimeria strains with limited scope of protection against an ever-evolving and widespread pathogen. The continual emergence of drug-resistant strains of Eimeria, coupled with the increasing regulations and bans on the use of anticoccidial drugs in commercial poultry production, urges the need for novel approaches and alternative control strategies. Because of the complexity of the host immunity and the parasite life cycle, a comprehensive understanding of host-parasite interactions and protective immune mechanisms becomes necessary for successful prevention and control practices. Recent progress in functional genomics technology would facilitate the identification and characterization of host genes involved in immune responses as well as parasite genes and proteins that elicit protective host responses. This study reviews recent coccidiosis research and provides information on host immunity, immunomodulation, and the latest advances in live and recombinant vaccine development against coccidiosis. Such information will help magnify our understanding of host-parasite biology and mucosal immunology, and we hope it will lead to comprehensive designs of nutritional interventions and vaccination strategies for coccidiosis.

The Biology of Avian Eimeria with an Emphasis on their Control by Vaccination

Studies on the biology of the avian species of Eimeria are currently benefiting from the availability of a comprehensive sequence for the nuclear genome of Eimeria tenella. Allied to some recent advances in transgenic technologies and genetic approaches to identify protective antigens, some elements are now being assembled that should be helpful for the development of a new generation of vaccines. In the meantime, control of avian coccidiosis by vaccination represents a major success in the fight against infections caused by parasitic protozoa. Live vaccines that comprise defined populations of oocysts are used routinely and this form of vaccination is based upon the long-established fact that chickens infected with coccidial parasites rapidly develop protective immunity against challenge infections with the same species. Populations of wild-type Eimeria parasites were the basis of the first live vaccines introduced around 50 years ago and the more recent introduction of safer, live-attenuated, vaccines has had a significant impact on coccidiosis control in many areas of the world. In Europe the introduction of vaccination has coincided with declining drug efficacy (on account of drug resistance) and increasing concerns by consumers about the inclusion of in-feed medication and prospects for drug residues in meat. The use of attenuated vaccines throughout the world has also stimulated a greater interest in the vaccines that comprise wild-type parasites and, during the past 3 years worldwide, around 3x10(9) doses of each type of vaccine have been used. The need for only small numbers of live parasites to induce effective protective immunity and the recognition that Eimeria spp. are generally very potent immunogens has stimulated efforts to develop other types of vaccines. None has succeeded except for the licensing, within several countries in 2002, of a vaccine (CoxAbic vaccine; Abic, Israel) that protects via the maternal transfer of immunoglobulin to the young chick. Building on the success of viral vaccines that are delivered via the embryonating egg, an in ovo coccidiosis vaccine (Inovocox, Embrex Inc.) is currently in development. Following successful field trials in 2001, the product will be ready for Food and Drug Administration approval in 2005 and a manufacturing plant will begin production for sale in late 2005. Limited progress has been achieved towards the development of subunit or recombinant vaccines. No products are available and studies to identify potential antigens remain compromised by an absence of effective in vitro assays that correlate with the induction of protective immunity in the host. To date, only a relatively small portfolio of molecules has been evaluated for an ability to induce protection in vivo. Although Eimeria are effective immunogens, it is probable that to date none of the antigens that induce potent protective immune responses during the course of natural infection has been isolated.

Intestinal immune responses to coccidiosis

Intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and production efficiency of livestock and poultry. Coccidiosis is an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria. Infection with coccidia parasites seriously impairs the growth and feed utilization of chickens and costs the US poultry industry more than $1.5 billion in annual losses. Although acquired immunity to Eimeria develops following natural infection, due to the complex life cycle and intricate host immune response to Eimeria, vaccine development has been difficult and a better understanding of the basic immunobiology of pertinent host-parasite interactions is necessary for developing effective immunological control strategies against coccidiosis. Chickens infected with Eimeria produce parasite specific antibodies in both the circulation and mucosal secretions but humoral immunity plays only a minor role in protection against this disease. Rather, recent evidence implicates cell-mediated immunity as the major factor conferring resistance to coccidiosis. This review will summarize current understanding of the avian intestinal immune system and its response to Eimeria as well as provide a conceptual overview of the complex molecular and cellular events involved in intestinal immunity to coccidiosis. It is anticipated that increased knowledge of the interaction between parasites and host immunity will stimulate the birth of novel immunological and molecular biological concepts in the control of intestinal parasitism.

Immunomodulatory effects of oat beta-glucan administered intragastrically or parenterally on mice infected with Eimeria vermiformis

The immunostimulatory effect of intragastrically or parenterally administered beta-(1-->3; 1-->4) glucan, extracted from oats (ObetaG), on disease resistance to Eimeria vermiformis was studied in C57BL/6 mice. Multiple administrations of ObetaG by intragastric or subcutaneous routes reduced fecal oocyst shedding compared to the non-treated control group. The administration of ObetaG by subcutaneous route resulted in higher levels of total serum immunoglobulins and antigen (sporozoite and merozoite)-specific immunoglobulins as compared with the non-treated group. To evaluate the effect of a single subcutaneous dose, groups of mice were treated with ObetaG 2 days before E. vermiformis infection, at the time of infection and at 2 or 6 days after infection. From day 11 post-infection the oocyst discharge was significantly diminished (P<0.05-0.01) in the ObetaG-treated groups, except in those treated 6 days after infection, as compared to the non-treated control group. The proliferative responses to E. vermiformis sporozoite antigen of lymphocytes isolated from the spleen were significantly increased (P<0.05) when ObetaG was administered 2 days before or at the time of E. vermiformis infection. Lymphocyte proliferative responses to merozoite antigen were not influenced by treatment. In conclusion, ObetaG appeared to up-regulate immune mechanisms and provide enhanced resistance against eimerian coccidiosis in mice.

Genetic analysis of the essential components of the immunoprotective response to infection with Eimeria vermiformis

The immune responses generated after infection with Eimeria spp. are complex, include both cellular and humoral components, and lead to protection against re-infection. To facilitate the rational development of the next generation of anticoccidial vaccines it is important that the nature of the immunoprotective response against infection with Eimeria spp. is determined. In this brief report we discuss results that were obtained using a combination of genetic and cellular approaches to dissect the essential immune effector components that operate against infection with Eimeria vermiformis. Mice rendered deficient of immune function by targeted gene disruption at a variety of immune loci represent an integral component of our studies and include those with targeted gene disruption at loci that encode the B- and T-cell receptors (BCR, TCR), antigen presentation molecules and immune-effector molecules. Our studies demonstrated that TCR-alpha-beta + T cells are essential for immunoprotection during both primary and secondary infection. Moreover, during primary infection the major effector cell type is a population of major histocompatibility complex class II-restricted, interferon-gamma-producing TCR-alpha-beta T cell consistent with a T helper 1 phenotype. In addition, there is a supplementary role for another class of cells (presumably T cells) that are restricted to either non-classical antigen presentation molecules or classical major histocompatibilty complex class I loaded via an atypical pathway. Mice with a deficiency in interleukin-6 were slightly more susceptible to primary infection than intact animals, consistent with the reported effects of interleukin-6 upon the generation of T helper 1-type responses in vivo. In terms of the host response to re-infection, TCR-alpha-beta T cells were essential for immunity, but the requirement for specific cell subsets and effector mechanisms was much less stringent. Mice deficient in gamma-delta T cells, classical major histocompatibility complex class I, non-classical antigen presentation pathways, the cytokines interferon-gamma, interleukin-4, interleukin-6 and the cytolytic effector molecules perforin or FasL were completely immune to secondary infection. Moreover, major histocompatibility complex class II-deficient I-A-beta-/- mice were capable of mounting a substantial response to secondary infection, manifest by a 95% reduction in oocyst output compared with primary infection. These data have important consequences for the development of immune intervention strategies and indicate that vaccine development may be targeted toward the generation of a wider range of effector mechanisms than those that operate during primary infection.

Kinetics of specific immunoglobulin A, M and G production in the duodenal and caecal mucosa of chickens infected with Eimeria acervulina or Eimeria tenella

The development and appearance of antibody was studied in the intestine and serum from histocompatible GB1 chickens orally infected with oocysts of Eimeria acervulina (restricted to the duodenum) or Eimeria tenella (restricted to the caeca). The local immune response was measured as the specific antibody levels in the supernatants of intestinal fragments (duodenum and caecum) maintained in culture for 16 h at 41 degrees C, 5% CO2, 95% air. Specific IgM was detected 1 week after E. acervulina infection, and the specific IgA and IgG contents of the duodenum and caecum were significantly elevated (P < 0.001) after 2 weeks. The intestinal specific IgG content was raised. E. tenella infection resulted in specific IgA only in the parasitized area during the second week post-infection (P < 0.05). Specific IgM and IgG were both detected in the duodenum and caecum, respectively, 1 and 2 weeks p.i. Production of parasite-specific immunoglobulins was always significantly higher in the parasitized than in the unparasitized areas (caeca for E. acervulina, duodenum for E. tenella). This ex vivo culture assay of intestinal fragments used to measure the mucosal immune response of intestinal areas showed a significant production of specific IgA and IgM. In addition, high levels of IgG were also measured. The role of this specific IgG in Eimeria infection remains to be determined.

Variable levels of immunity to experimental Eimetia arizonensis infections in natural, seminatural, and laboratory populations of deer mice (Peromyscus maniculatus)

Acquired immunity to parasites may affect both host and parasite population dynamics. Although immunity has been studied experimentally in laboratory-reared hosts, less attention has focused on free-living animals. I examined acquired immunity of free-living deer mice (Peromyscus maniculatus) to naturally occurring and experimental infections of Eimeria arizonensis (Protozoa: Coccidia). In a mark – recapture study, I found evidence of complete immunity to natural infections in only 1 of 3 years and evidence of partial immunity in all years. I subsequently examined partial immunity to experimental infections by giving laboratory-reared, free-living, and enclosure populations of deer mice two or three consecutive E. arizonensis infections. Greater than 90% (13 of 14) of laboratory-reared animals developed immunity after only one exposure, suggesting that E. arizonensis is immunogenic. However, significantly fewer animals living under natural and seminatural conditions developed immunity after one exposure in two of three experiments. These observational and experimental results suggest that immunocompetence of free-living deer mice to E. arizonensis may be variable and may differ with respect to that of laboratory-reared animals.

The immunodominant Eimeria acervulina sporozoite antigen previously described as p160/p240 is a 19-kilodalton antigen present in several Eimeria species

A lambda Zap II cDNA expression library, constructed from Eimeria acervulina (PAPa46 strain) sporulated oocyst stage, was screened with sera raised to E. acervulina or Eimeria tenella oocysts in order to isolate clones coding for antigens common to the two species. Most of the clones isolated were derived from the same gene. Antisera raised to a recombinant glutathione-S-transferase fusion protein 1P reacted with an antigen of 19 kDa in immunoblot of E. acervulina sporulated and unsporulated oocysts. Immunofluorescence of E. acervulina sporozoites indicated that the antigen is located in the cytoplasm. The anti-1P antisera reacted on immunoblots of E. tenella with a 19-kDa antigen and by immunofluorescence on E. tenella, Eimeria maxima and Eimeria falciformis sporozoites, indicating that the antigen is conserved in Eimeria species. DNA sequencing indicated that the sequence was almost identical to that of clone cSZ1 previously described by Jenkins et al. using E. acervulina strain #12. The 1P insert hybridized to a 1150-nt mRNA from E. acervulina PAPa46 strain and strain #12, a size consistent with the observed molecular weight of the protein.

Production and characterization of monoclonal antibodies directed against Eimeria falciformis and cross-reactive with sporozoites from two species of avian coccidia

Monoclonal antibodies (mAbs) were obtained against the surface antigens of the Eimeria falciformis sporozoite by immunizing mice with whole homogenized sporozoite. The hybridomas were selected by their reactivities against oocyst extracts, then against glutaraldehyde-treated sporozoites. Three mAbs recognized both the surface of E. falciformis, E. tenella, and E. acervulina and their refractile bodies, whereas a fourth mAb recognized only one epitope on the refractile bodies. All mAbs bound to the same immunoaffinity-purified antigens in Western-blot analysis (P27 for E. falciformis and P25 for E. tenella and E. acervulina). Thus, the mAbs define at least two shared epitopes between sporozoite antigens from different eimerian species. Two of these mAbs are involved in the in vitro phagocytosis of E. falciformis sporozoites by macrophages and also in their lysis by neutrophils. Altogether, these properties showed that the four mAbs came from different activated B-cells. The P27 antigen recognized by our mAbs represents a major target of the in vitro destructive immune response.

Protective oral immunization of chickens against Eimeria tenella with sporozoite surface antigens

Antigens were extracted from the surface of Eimeria tenella sporozoites with a solution containing Triton X 100 (1%), sodium dodecyl sulphate (0.5%) Na deoxycholate (1%) and EDTA (1 mM). After removal of the detergents, these surface antigen preparations conferred an immunity that protected chickens against a subsequent infection (10(4) sporulated oocysts). The best results were obtained after two 250 micrograms injections of Al(OH)3 adsorbed antigens (oocyst output per g caecal material on Day 7 post infection: 2.39 x 10(7) +/- 0.32 x 10(7) oocysts for controls and 7.37 +/- 10(6) +/- 3.19 x 10(6) oocysts for vaccinated birds) and after four gastric intubations of liposome entrapped antigens (oocysts output on Day 7 postinfection: 2.75 x 10(6) +/- 2.02 x 10(6) g-1 caecal material). These results represented respectively 70 and 88% protection indexes. Studies on the systemic and local antibody response after one or several infections of chickens with the parasite indicated at least 20 different molecules in the detergent antigens which are classified after immunoblotting according to their properties.

Immunocytochemical and immunoelectron microscopy study of dendritic cells in the caecal tonsils of chickens infected with Eimeria tenella

In the present study S-100 protein containing cells in the caecal tonsil were investigated, both at light microscopic and at electron microscopic levels, after oral coccidia inoculation (Eimeria tenella). The birds were infected with a single (Day 0) or two (Days 0 and 21) infective doses of 500 oocysts. Immunoelectron reactivity for S-100 protein was demonstrated in infected chickens, but not in controls. It was found in follicular dendritic cells and interdigitating dendritic cells which were present in the germinal center and diffuse lymphoid tissue respectively, both of them being located in the deep lymphoid tissue near the muscular layer and around the deep glands. Outside the lymphoid tissue, immunoreactivity for S-100 protein was found in cells lying between the epithelial cells of the deep crypt epithelium. Positivity for S-100 protein was observed at 3, 12, 18, 24 and 48 h after the first inoculation as well as on Days 3, 5, 6, 7, 8, 25 and 30 of the experiment. Positive reaction for S-100 protein was detected both while schizont (the more immunogenic stage) development occurs and the number of sporozoites in the caeca lumen was higher, as well as when the production of oocysts reached a maximum. Complementary studies demonstrated that S-100 positive dendritic cells gave a negative reaction for esterase activity, whereas a subset of S-100 negative intraepithelial lymphocytes located between epithelial cells lining the deep glands exhibited esterase activity. These esterase positive cells are hypothesized to be involved in the regulation of local defences.

Detection of mucosal immune responses in chickens after immunization or infection

In order to measure mucosal antibody responses in the chicken intestine an ELISA-based assay was developed that was able to detect antigen-specific antibodies in an isotype-specific way. Locally produced antibodies could be detected after overnight culture at 37 degrees C. In particular the production of IgA, more than IgM and IgG, was significantly increased by immunization of the animals with K99 pilus antigen or by infection with Eimeria tenella parasites. Data presented here indicate that the assay can be used to estimate the magnitude of the mucosal antibody response in experimental conditions where antibody levels in bile or intestinal contents were not significantly changed.

In vitro interactions between murine neutrophils and Eimeria falciformis sporozoites

The in vitro interactions between elicited mouse peritoneal neutrophils, antibodies and newly excysted sporozoites of Eimeria falciformis resulted in lysis of the parasite. This lysis required the presence of a heat-labile component of normal mouse serum, and was antibody- and cell-concentration-dependent. Under optimal conditions (serum dilution = 1/192, effector cell/sporozoite = 10/1) this lysis, which began after incubation at 37 degrees C for 4 h, was nearly complete after 18 h. It began by opsonization of the sporozoites by antibodies and complement. Inhibition studies performed with inhibitors of neutrophil function did not enable us to determine the mechanism of this extracellular lysis (oxidative respiratory burst or enzyme release), since only metal chelators, lysosomotropic reagents and compounds known to interfere with adenylate cyclase activity were truly inhibitory.

In vitro interactions between murine macrophages and Eimeria falciformis sporozoites

A short-term (2 h) assay was used to investigate the in vitro fate of Eimeria falciformis sporozoites in murine peritoneal macrophages. In minimal medium, uptake of sporozoites was low by both normal (naive) and immune macrophages. However, when heat-inactivated serum from immune mice was added to the incubation medium, sporozoite uptake was much more efficient. Sporozoite lysis was observed only in immune macrophages and required both antibodies and complement. Pretreatment of immune macrophages with chloroquine inhibited sporozoite lysis and resulted in an accumulation of sporozoites within the cells. Immunoabsorption assays revealed that IgG2a was the major isotype mediating entry of sporozoites into macrophages, both in early (6 days post-primary) and late (second) infections.