Eimeria tenella: effects of immunity on sporozoites within the lumen of the small intestine

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.

Still naïve or primed: Anticoccidial vaccines call for memory

Despite decades of investigation to clarify protective mechanisms of anticoccidial responses, one crucial field is neglected, that is, protective memory responses in primed birds. Protective memory immunity is critical for host resistance to reinfection and is the basis of modern vaccinology, especially in developing successful subunit vaccines. There are important differences between the immune responses induced by infections and antigens delivered either as killed, recombinant proteins or as live, replicating vector vaccines or as DNA vaccines. Animals immunized with these vaccines may fail to develop protective memory immunity, and is still naïve to Eimeria infection. This may explain why limited success is achieved in developing next-generation anticoccidial vaccines. In this review, we try to decipher the protective memory responses against Eimeria infection, assess immune responses elicited by various anticoccidial vaccine candidates, and propose possible approaches to develop rational vaccines that can induce a protective memory response to chicken coccidiosis.

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.

Parasite-specific proliferative responses of chicken spleen cells upon in vitro stimulation with Eimeria tenella antigen

This study aimed to set up methodology to monitor parasite-specific T-cell activation in vitro using Eimeria tenella-infected chickens. A sonicated E. tenella sporozoite protein preparation was used for the activation of chicken spleen cell cultures. Proliferation assessed by 3H-thymidin incorporation or blast transformation of T-cells assessed by immunofluorescence labelling and flow cytometry were used as read-outs for activation. Results showed that E. tenella-specific proliferation was detected in cultures of spleen cells collected in a ‘window’ between 8 and 14 days after primary infection. However, due to high variation in proliferative responses between individuals and to high background proliferation, large numbers of observations were needed to obtain significant results. Moreover, the outcome was not improved by increasing the infection dose to chickens or by depletion of T-cell receptor (TCR) γ/δ expressing cells from cultures. An E. tenella-specific blast transformation response was observed for TCRα/β expressing cells within the same ‘window’, confirming the identity of the responding cells as classic T-cells. Thus, it is possible to study the kinetics of E. tenella-specific T-cell responses in vitro. However, more in-depth phenotypic identification of the responding T-cells could improve the methodology.

Expression of perforin, granzyme A and Fas ligand mRNA in caecal tissues upon Eimeria tenella infection of naïve and immune chickens

Cytotoxic cells of the immune system may kill infected or transformed host cells via the perforin/granzyme or the Fas ligand (FasL) pathways. The purpose of this study was to determine mRNA expression of perforin, granzyme A and FasL in Eimeria tenella-infected tissues at primary infection and infection of immune chickens as an indirect measure of cytotoxic cell activity. Chickens were rendered immune by repeated E. tenella infections, which were manifested as an absence of clinical signs or pathological lesions and significantly reduced oocyst production upon challenge infection. During primary E. tenella infection, perforin, granzyme A and FasL mRNA expression in caecal tissue was significantly increased at 10 days after infection, compared to uninfected birds. In contrast, at infection of immune birds, perforin and granzyme A mRNA expression in caecal tissue was significantly increased during the early stages of E. tenella challenge infection, days 1-4, which coincided with a substantial reduction of parasite replication in these birds. These results indicate the activation of cytotoxic pathways in immune birds and support a role for cytotoxic T cells in the protection against Eimeria infections.

Monitoring of local CD8β-expressing cell populations during Eimeria tenella infection of naïve and immune chickens

The purpose of this study was to monitor abundance and activation of local CD8β-expressing T-cell populations during Eimeria tenella infections of naïve chickens and chickens immune by previous infections. Chickens were infected with E. tenella up to three times. Caecal T-cell receptor (TCR) γ/δ-CD8β+ cells (cytotoxic T lymphocytes; CTL) and TCRγ/δ+CD8β+ cells were characterized with respect to activation markers (blast transformation, CD25 and cell surface CD107a). Cells were also induced to degranulate in vitro as a measure of activation potential. Major findings included a prominent long-lasting, up to 6 weeks, increase in the proportion of CTL among caecal CD45+ cells in the later stages after primary E. tenella infection. These CTL also showed clear signs of activation, that is blast transformation and increased in vitro induced degranulation. At second and third E. tenella infection, chickens showed strong protective immunity but discrete signs of cellular activation were observed, for example increased in vitro induced degranulation of CTL. Thus, primary E. tenella infection induced clear recruitment and activation of local CTL. Upon subsequent infections of strongly immune chickens cellular changes were less prominent, possibly due to lower overall numbers of cells being activated because of the severe restriction of parasite replication.

Influence of organic zinc supplementation on the antioxidant status and immune responses of broilers challenged with Eimeria tenella

An experiment was conducted to investigate the influence of Zn supplementation on the performance, antioxidant status, and immune responses of broilers challenged with Eimeria tenella. A total of 384 male broilers (1 d old) were assigned to 8 treatments consisting of 8 replicates of 6 chicks each. A basal corn-soybean meal diet (29.6 mg of Zn/kg) was supplemented with methionine hydroxyl analog-Zn chelate at 0, 20, 40, and 60 mg/kg of diet. At 21 d of age, birds were orally gavaged with 1.5 × 10(4) sporulated E. tenella oocysts. Dietary Zn supplementation had no effect on growth performance of either the challenged or nonchallenged birds. Activities of Cu-Zn superoxide dismutase and glutathione peroxidase were increased (P < 0.001) with increasing Zn levels in both the challenged and nonchallenged groups. Lipid peroxidation tended to be reduced (P = 0.08) at Zn inclusion of 20 and 40 mg/kg. In vitro lymphocyte proliferation responses to mitogen concanavalin A and LPS were not influenced by dietary Zn or challenge. The main effects of Zn level and challenge were significant for secretory IgA on d 28 (P < 0.01) and 35 (P < 0.001). During both periods, secretory IgA of birds receiving dietary Zn supplementation was higher (P < 0.05) than that of those receiving no Zn supplementation. Birds fed Zn supplementation excreted fewer oocysts in the excreta than those receiving no Zn supplement (P < 0.001). Results indicated that organic Zn supplementation reduced oxidative stress and improved some immune responses irrespective of whether birds were healthy or challenged with E. tenella.

Enhanced egress of intracellular Eimeria tenella sporozoites by splenic lymphocytes from coccidian-infected chickens

Egress, which describes the mechanism that some intracellular parasites use to exit from parasitophorous vacuoles and host cells, plays a very important role in the parasite life cycle and is central to Eimeria propagation and pathogenesis. Despite the importance of egress in the intracellular parasite's life cycle, very little information is known on this process compared to other steps, e.g., invasion. The present study was conducted to investigate the interplay between the host adaptive immune system and Eimeria egression. Splenic lymphocytes or soluble immune factors were incubated with parasite-infected host cells for 3 or 5 h, and the percentage of egress was calculated according to an established formula. Viability of egressed parasites and host cells was tested using trypan blue exclusion and annexin V and propidium iodide staining, respectively. We found that premature egression of sporozoites from Eimeria tenella-infected primary chicken kidney cells or from chicken peripheral blood mononuclear cells occurred when the cells were cocultured in vitro with spleen lymphocytes from E. tenella-infected chickens but not when they were cocultured with splenocytes from uninfected chickens. Eimeria-specific antibodies and cytokines (gamma interferon [IFN-γ], interleukin-2 [IL-2], and IL-15), derived from E. tenella-primed B and T lymphocytes, respectively, were capable of promoting premature egress of sporozoites from infected host cells. Both egressed parasites and host cells were viable, although the latter showed reduced reinvasion ability. These results suggest a novel, immune-mediated mechanism that the host exploits to interrupt the normal Eimeria life cycle in vivo and thereby block the release of mature parasites into the environment.

CD8+ T cell-coccidia interactions

Host responses to coccidian parasites involve many facets of the immune system, including antigen-specific as well as antigen-nonspecific components. Hyun Lillehoj and James Trout here review the evidence that cell-mediated responses are probably the main line of defense against coccidial infection.

Gene discovery in Eimeria tenella by immunoscreening cDNA expression libraries of sporozoites and schizonts with chicken intestinal antibodies

Specific antibodies were produced ex vivo from intestinal culture of Eimeria tenella infected chickens. The specificity of these intestinal antibodies was tested against different parasite stages. These antibodies were used to immunoscreen first generation schizont and sporozoite cDNA libraries permitting the identification of new E. tenella antigens. We obtained a total of 119 cDNA clones which were subjected to sequence analysis. The sequences coding for the proteins inducing local immune responses were compared with nucleotide or protein databases and with expressed sequence tags (ESTs) databases. We identified new Eimeria genes coding for heat shock proteins, a ribosomal protein, a pyruvate kinase and a pyridoxine kinase. Specific features of other sequences are discussed.

Cell: sporozoite interactions and invasion by apicomplexan parasites of the genus Eimeria

The site specificity that avian Eimeria sporozoites and, to a more limited degree, other apicomplexan parasites exhibit for invasion in vivo suggests that specific interactions between the sporozoites and the target host cells may mediate the invasion process. Although sporozoite motility and structural and secreted antigens appear to provide the mechanisms for propelling the sporozoite into the host cell,there is a growing body of evidence that the host cell provides characteristics by which the sporozoites recognise and interact with the host cell as a prelude to invasion. Molecules on the surface of cells in the intestinal epithelium, that act as receptor or recognition sites for sporozoite invasion, may be included among these characteristics. The existence of receptor molecules for invasion by apicomplexan parasites was suggested by in vitro studies in which parasite invasion was inhibited in cultured cells that were treated with a variety of substances designed to selectively alter the host cell membrane. These substance included cationic compounds or molecules, enzymes that cleave specific linkages, protease inhibitors, monoclonal antibodies, etc. More specific evidence for the presence of receptors was provided by the binding of parasite antigens to specific host cell surface molecules. Analyses of host cells have implicated 22, 31, and 37 kDa antigens, surface membrane glycoconjugates,conserved epitopes of host cells and sporozoites, etc., but no treatment that perturbs these putative receptors has completely inhibited invasion of the cells by parasites. Regardless of the mechanism,sporozoites of the avian Eimeria also invade the same specific sites in foreign host birds that they invade in the natural host. Thus, site specificity for invasion may be a response to characteristics of the intestine that are shared by a number of hosts rather than to a unique trait of the natural host. Protective immunity elicited against avian Eimeria species is not manifested in a total blockade of parasite invasion. In fact, the effect of immunity on invasion differs according to the eliciting species and depends upon the area of the intestine that is invaded. Immunity produced against caecal species of avian Eimeria, for example Eimeria tenella and Eimeria adenoeides, inhibits subsequent invasion by homologous or heterologous challenge species, regardless of the area of the intestine that the challenge species invade. Conversely, in birds immunised with upper intestinal species, Eimeria acervulina and Eimeria meleagrimitis, invasion by challenge species is not decreased and often is significantly increased.

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.

Role of T lymphocytes and cytokines in coccidiosis

Development of a vaccine for avian coccidiosis has been hampered by lack of understanding of the various components of the host immune system leading to protective immunity. Clear understanding of the cellular dichotomy in cytokine production in mice and the availability of immunological reagents, as well as gene knock-out mice, now makes in-depth immunological study in this species feasible. From studies of various parasitic infection models in mice, it is becoming clear that complex regulation by cytokines is involved in host immunity. Furthermore, the studies in mice clearly indicated an important role of various effector mechanisms involving T lymphocytes, macrophages, natural killer (NK) cells and cytokines in resistance to coccidiosis. In comparative studies of coccidiosis in chickens, in-vivo and in-vitro studies revealed that interferon-gamma, tumor necrosis factor and transforming growth factor-beta are induced following Eimeria infection. Depletion studies revealed the importance of CD8+TCR-alpha-beta+ T lymphocytes in host protective immunity to avian coccidiosis. Taken together, studies in mice and chickens are providing a better understanding of the role of effector cells and soluble factors which control immune responses to Eimeria parasites.

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.

Avian gut-associated lymphoid tissues and intestinal immune responses to Eimeria parasites

Coccidiosis, an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria, seriously impairs the growth and feed utilization of livestock and poultry. Host immune responses to coccidial infection are complex. Animals infected with Eimeria spp. produce parasite-specific antibodies in both the circulation and mucosal secretions. However, it appears that antibody-mediated responses play a minor role in protection against coccidiosis. Furthermore, there is increasing evidence that cell-mediated immunity plays a major role in resistance to infection. T lymphocytes appear to respond to coccidial infection through both cytokine production and a direct cytotoxic attack on infected cells. The exact mechanisms by which T cells eliminate the parasites, however, remain unclear. Although limited information is available on the intestinal immune system of chickens, gut lymphoid tissues have evolved specialized features that reflect their role as the first line of defense at mucosal surfaces, including both immunoregulatory cells and effector cells. This review summarizes our current understanding of the avian intestinal immune system and mucosal immune responses to Eimeria spp., providing an overview of the complex cellular and molecular events involved in intestinal immune responses to enteric pathogens.

Immunization against experimental coccidiosis produces contrasting results in inbred mice of differing susceptibility to infection

Pretreatment of inbred mice with intravenous and/or intraperitoneal injection of an antigen prepared from sporozoites of Eimeria vermiformis modulated the course of infection with the parasite in a manner that depended on the resistance-susceptibility phenotype of the host. Mice with a resistant background (BALB) produced more oocysts and those with a susceptible background (C57BL) produced fewer oocysts than their respective controls. The optimum conditions for producing these effects were established, and evidence is presented which suggests that the phenomenon might also apply in the target host, the chicken.

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.

Comparison of selected protocols for the generation of IgA isotype monoclonal antibodies against the gut parasite, Eimeria tenella

Investigations into the role of mucosal IgA in the protective immune response to alimentary tract parasites could be facilitated by the production of specific IgA monoclonal antibodies. To this end, we sought to generate IgA hybridomas against sporozoites of the protozoan, Eimeria tenella using different protocols. Of the methods investigated, intra-enteric priming followed by intravenous boosting of germ-free mice, using splenic lymphocytes in fusions, optimised the yield of IgA hybridomas. Using this protocol, 7/27 specific anti-Eimeria hybridoma antibodies isolated were of IgA isotype. When lymphocytes from mesenteric lymph nodes (MLN) were used in fusions more non-specific IgA secretors were produced than when splenic lymphocytes were used, but the yield of specific anti-Eimeria IgA secreting hybridomas was not improved. By all protocols, a total of nine IgA secreting hybridomas were identified of which eight have been cloned for further studies.

In situ immunocytochemical detection of cells containing antibodies specific for Eimeria tenella antigens

A three-step immunocytochemical method for the in situ detection of antibodies specific for Eimeria tenella has been developed. The method is based on the binding of E. tenella antigens to antibodies in cryostat sections of chicken tissues and the recognition of these antigens by rabbit antiserum specific for E. tenella or mouse monoclonal antibodies specific for E. tenella. The rabbit antiserum and mouse monoclonal antibodies were revealed by the immunoperoxidase technique. Suspensions of sonicated sporulated oocysts, incubated with or without various concentrations of the non-ionic detergents Triton X-100 (TX-100) or Nonidet P-40 (NP-40), were used as antigen. Cells containing antibodies specific for E. tenella were detected only when detergent extracts of sonicated sporulated oocysts were used. After chickens were intravenously immunized with a suspension of sonicated sporulated oocyst antigen, cells containing antibodies specific for E. tenella antigens were detected in the red pulp of the spleen. After simultaneous immunoenzyme staining for isotype and antigen specificity, the E. tenella-specific antibody-containing cells were of the IgM isotype after the primary immunization and of the IgM and IgG isotype after the booster immunization. Immune complexes specific for E. tenella on the surfaces of follicular dendritic cells in the germinal centers were also stained. Chickens were also orally infected with sporulated oocysts. In these experiments, cells containing antibodies specific for E. tenella were detected in the lamina propria of the ceca and in the red pulp of the spleen. Specific immune complexes were also detected in the germinal centers of the cecal tonsils. When detergent extracts of sonicated sporulated oocysts were characterized by immunoblotting, rabbit antiserum specific for E. tenella reacted with proteins ranging in size from 16 kDa to 200 kDa, with major bands of 20 kDa, 24 kDa, 45 kDa, and 100 kDa. Monoclonal antibodies specific for E. tenella recognized only proteins of low molecular weight (20 kDa and 24 kDa) or high molecular weight (80-100 kDa). Immune chicken serum reacted with proteins of low and high molecular weight but especially with proteins of 100 kDa and 113 kDa. This method is the first by which immune complexes and cells containing antibodies specific for parasitic antigens can be detected in situ and may be of value for studies of the local humoral immune response to E. tenella in the mucosa of chickens.

Changes in the messenger RNA population during sporulation of Eimeria maxima

Messenger RNA has been extracted from oocysts of Eimeria maxima. Using the techniques of in vitro translation and SDS-polyacrylamide gel electrophoresis, we have been able to show that major changes in gene transcription occur during sporulation. Following an overall reduction in the abundance of many mRNAs, several genes identified as the result of an increase in the abundance of their transcripts, are highly expressed during the latter stages of sporulation. A study of two genes whose transcription is down-regulated has provided evidence which shows that both single copy and repetitive sequences are regulated during sporulation of the oocyst.

Eimeria tenella: local antibodies and interactions with the sporozoite surface

Using fixed sporozoites in a 3-layer immunofluorescence assay (TLIFA), class-specific, parasite-specific antibody responses in chicks to single-pulse infection with Eimeria tenella have been studied in gut contents and bile as well as plasma and feces. After infection with 10(3) oocysts, IgA antibody was first detected in the duodenal lumen, then in bile, plasma, cecum, and the distal small intestine. The kinetics of the bile IgA response correlated with that in plasma and peaked 9 days post-infection (d.p.i.); IgM was detected in gut contents and bile as well as plasma, and IgG was occasionally detected in gut contents, especially in the duodenum. In some experiments, IgA was detected in gut contents and bile to at least 21 d.p.i. Infection with 10(5) oocysts resulted in an earlier and increased response and relatively high IgG titers in cecal contents. Coproantibody was detected inconsistently and at low titer. When sporozoites that excysted in vitro were incubated in specific, antibody-positive (9 d.p.i.) cecal contents, some complement-mediated IgG-associated anti-sporozoite effects were observed; however, the major effect of cecal contents and the only effect of bile was a non-lethal agglutination of living sporozoites. By fractionation of cecal contents and immunoblotting this was confirmed to be IgA mediated; IgA antibodies in cecal contents and bile after infection were shown to bind to sporozoite membrane antigens by surface fluorescence as well as agglutination. Agglutination detected anti-sporozoite antibody in gut contents and bile up to 21 d.p.i., peaking between 7 and 13 d.p.i., corresponding with TLIFA results.(ABSTRACT TRUNCATED AT 250 WORDS)

Eimeria vermiformis and E. mitis: inhibition of development in vivo by cyclosporin A

Treatment of the host (Mus musculus, Gallus domesticus) with cyclosporin A during infection with Eimeria vermiformis or E. mitis resulted in a reduction in the numbers of oocysts passed in the feces and/or a delay in patency. The general immunosuppressive effects of the treatment were confirmed in chickens by monitoring their antibody responses to human erythrocytes and lymphoproliferative responses to phytohemagglutinin. Nevertheless, mice and chickens treated with cyclosporin A during a primary infection with E. vermiformis or E. mitis, respectively, were immune to subsequent challenge with these organisms. Thus, cyclosporin A did not interfere with priming. The antiparasite effect of the drug did not allow an evaluation of its effect on established immunity to the coccidia when it was administered at the time of challenge. In an exceptional treated chicken, however, delayed patency of the challenge infection was followed by the production of a number of oocysts similar to that found in unprimed animals. This suggests that the mechanisms of immunity to challenge may be susceptible to disruption by cyclosporin A.

Eimeria tenella: immunological diversity between asexual generations

In the development of a normal strain, WIS, of Eimeria tenella there are three generations of schizogony whereas in an attenuated line, WIS-F-96, derived from WIS, the second and third are absent. Chickens immunized by infection with WIS-F-96, however, were highly resistant to oral challenge with sporulated oocysts of WIS, and histological studies indicated that the immune response was directed against the sporozoites from that challenge inoculum. When challenge of the WIS-F-96-primed chickens consisted of second generation merozoites of WIS (inoculated intracaecally), immunity was less pronounced and the histological data indicated that the merozoites proceeded to develop normally in these birds. These indications of immunological diversity between the merozoites of the first and second generations of schizogony of E. tenella WIS correlated with the results of preliminary studies of the antigenic composition of these developmental stages.

Mediation of immunity to Eimeria vermiformis in mice by L3T4+ T cells

Immunity to infection with Eimeria vermiformis was transferred in NIH mice by both the nylon wool-adherent (B-cell-enriched) and nonadherent (T-cell-enriched) fractions of lymphocytes (spleen and mesenteric lymph node) taken from infected donors. Transfer was more variable with the adherent fraction, and when contaminating T cells were removed by treatment with anti-Thy1 monoclonal antibody (MAb) and complement, this fraction lost all protective activity. The protective effect of T-cell-enriched populations of mesenteric lymphocytes was abrogated by treatment with anti-L3T4 MAb and complement in vitro before transfer or by opsonization with this MAb in vitro before intravenous inoculation into recipients. Similar treatments of cells with anti-Lyt2 MAb did not have this effect, confirming that Thy1+ L3T4+ cells mediate the adoptive transfer of immunity to E. vermiformis. Thy1+ L3T4+ cells were also shown to limit the replication of E. vermiformis in primary infections: mice depleted of this subset (by thymectomy followed by intravenous injection of anti-L3T4 MAb) passed greater numbers of oocysts over a longer period of time than did mice similarly depleted of Lyt2+ cells.