Further investigation of the characteristics and biological function of Eimeria tenella apical membrane antigen 1

Eimeria tenella rhoptry neck protein 2 plays a key role in the process of invading the host intestinal epithelium

The Apicomplexa parasitic phylum rhoptry neck protein 2 (RON2) plays a key role in the process of invading host cells. Eimeria tenella, an intracellular protozoan shares a similar conserved invasion pattern. However, whether E. tenella RON2 participates in the process of invading the host intestinal epithelium is poorly understood. In this study, the sequence of EtRON2 was analyzed and expressed. The expression of the truncated extracellular N-terminal fragment of EtRON2 (403-700 aa, designated EtRON2403-700) with a molecular mass of 38.3 kDa. EtRON2 in the sporozoite protein was detected at 151.4 kDa by rabbit anti-rEtRON2403-700 antibody. Immunofluorescence results showed that EtRON2 was mainly localized to the nucleus and apex of the E. tenella sporozoite. qPCR results showed that the highest expression level of EtRON2 was detected in sporulated oocysts compared with other developmental stages of E. tenella. In vitro invasion inhibition assays showed that the capacity of sporozoites to invade DF-1 cells was significantly inhibited after pretreatment with the rabbit anti-rEtRON2403-700 antibody. Silencing the EtRON2 gene by RNA interference (RNAi) significantly inhibited EtRON2 expression and significantly reduced the invasion of DF-1 cells by sporozoites. In vivo experiments revealed a significant decrease parasite burden and oocyst outputs in chicks after infection with EtRON2 gene-silenced sporozoites by cloacal inoculation. Recombinant EtRON2403-700 (rEtRON2403-700) immunizes chicks effectively against E. tenella infection by inducing humoral immunity and upregulating IFN-γ and CD8+ T lymphocytes. Furthermore, chicks exhibited increased relative weight gain rates, lower cecum lesion scores, and reduced oocyst outputs during the E. tenella challenge. H&E staining showed that the cecum tissue of chicks immunized with rEtRON2403-700 showed relatively mild histopathological changes. In conclusion, the results of this study demonstrated that EtRON2 plays a key role in E. tenella invasion of the host intestinal epithelium and provides a potential target for vaccines against E. tenella infection.

Eimeria: Navigating complex intestinal ecosystems

Eimeria is an intracellular obligate apicomplexan parasite that parasitizes the intestinal epithelial cells of livestock and poultry, exhibiting strong host and tissue tropism. Parasite-host interactions involve complex networks and vary as the parasites develop in the host. However, understanding the underlying mechanisms remains a challenge. Acknowledging the lack of studies on Eimeria invasion mechanism, we described the possible invasion process through comparative analysis with other apicomplexan parasites and explored the fact that parasite-host interactions serve as a prerequisite for successful recognition, penetration of the intestinal mechanical barrier, and completion of the invasion. Although it is recognized that microbiota can enhance the host immune capacity to resist Eimeria invasion, changes in the microenvironment can, in turn, contribute to Eimeria invasion and may be associated with reduced immune capacity. We also discuss the immune evasion strategies of Eimeria, emphasizing that the host employs sophisticated immune regulatory mechanisms to suppress immune evasion by parasites, thereby sustaining a balanced immune response. This review aims to deepen our understanding of Eimeria-host interactions, providing a theoretical basis for the study of the pathogenicity of Eimeria and the development of novel anticoccidial drugs.

Global profiling of protein S-palmitoylation in the second-generation merozoites of Eimeria tenella

The intracellular protozoan Eimeria tenella is responsible for avian coccidiosis which is characterized by host intestinal damage. During developmental cycle, E. tenella undergoes versatile transitional stages such as oocyst, sporozoites, merozoites, and gametocytes. These developmental transitions involve changes in cell shape and cell size requiring cytoskeletal remodeling and changes in membrane proteins, which may require transcriptional and translational regulations as well as post-translational modification of proteins. Palmitoylation is a post-translational modification (PTM) of protein that orchestrates protein targeting, folding, stability, regulated enzymatic activity and even epigenetic regulation of gene expression. Previous research revealed that protein palmitoylation play essential role in Toxoplasma gondii, Trypanosoma cruzi, Trichomonas vaginalis, and several Plasmodium parasites. Until now, there is little information on the enzymes related to palmitoylation and role of protein acylation or palmitoylation in E. tenella. Therefore, palmitome of the second-generation merozoite of E. tenella was investigated. We identified a total of 2569 palmitoyl-sites that were assigned to 2145 palmitoyl-peptides belonging to 1561 protein-groups that participated in biological processes including parasite morphology, motility and host cell invasion. In addition, RNA biosynthesis, protein biosynthesis, folding, proteasome-ubiquitin degradation, and enzymes involved in PTMs, carbohydrate metabolism, glycan biosynthesis, and mitochondrial respiratory chain as well as vesicle trafficking were identified. The study allowed us to decipher the broad influence of palmitoylation in E. tenella biology, and its potential roles in the pathobiology of E. tenella infection. Raw data are publicly available at iProX with the dataset identifier PXD045061.

What Do We Know about Surface Proteins of Chicken Parasites Eimeria?

Poultry is the first source of animal protein for human consumption. In a changing world, this sector is facing new challenges, such as a projected increase in demand, higher standards of food quality and safety, and reduction of environmental impact. Chicken coccidiosis is a highly widespread enteric disease caused by Eimeria spp. which causes significant economic losses to the poultry industry worldwide; however, the impact on family poultry holders or backyard production-which plays a key role in food security in small communities and involves mainly rural women-has been little explored. Coccidiosis disease is controlled by good husbandry measures, chemoprophylaxis, and/or live vaccination. The first live vaccines against chicken coccidiosis were developed in the 1950s; however, after more than seven decades, none has reached the market. Current limitations on their use have led to research in next-generation vaccines based on recombinant or live-vectored vaccines. Next-generation vaccines are required to control this complex parasitic disease, and for this purpose, protective antigens need to be identified. In this review, we have scrutinised surface proteins identified so far in Eimeria spp. affecting chickens. Most of these surface proteins are anchored to the parasite membrane by a glycosylphosphatidylinositol (GPI) molecule. The biosynthesis of GPIs, as well as the role of currently identified surface proteins and interest as vaccine candidates has been summarised. The potential role of surface proteins in drug resistance and immune escape and how these could limit the efficacy of control strategies was also discussed.

Combined oral immunization with probiotics Entercoccus faecalis delivering surface-anchored Eimeria tenella proteins provide protective efficacies against homologous infection in chickens

Background and Objectives

Avian coccidiosis is an intestinal parasitic disease exerting a highly negative impact on the global poultry industry. The aim of the present study is to evaluate the immune protective efficacies against Eimeria tenella infection in chickens orally immunized with combined recombinant probiotics Entercoccus faecalis (E. faecalis) delivering surface-anchored E. tenella proteins.

Methods

Four kinds of novel probiotics vaccines that surface-expressing four Eimeria tenella (E. tenella) proteins EtAMA1, EtIMP1, EtMIC2 and Et3-1E were produced, respectively. The expression of four target proteins on the surface of recombinant bacteria was detected by Western blot and indirect immunofluorescence assay (IFA). Then the four kinds of recombinant E. faecalis were combined to immunize chickens via oral route in different combinations. The immunizations were performed three times at two-week intervals, and each for three consecutive days. After immunizations, chickens in each immunized group were orally challenged with E. tenella sporulated oocysts. The immune responses and protective efficacies against homologous infection were evaluated.

Results

The results showed that three or four live recombinant E. faecalis induced effective antigen-specific humoral, intestinal mucosal immune responses, stimulated peripheral T lymphocytes proliferation, and displayed partial protections against homologous challenge as measured by cecal lesions, oocyst shedding, and body weight gain (BWG). Notably, higher levels of protective efficacies were observed when the four recombinant E. faecalis delivering target proteins were combined.

Conclusion

Chickens orally administrated with three or four, especially the four combined recombinant E. faecalis stimulated specific immune responses, which provided anti-coccidial effects. This study offers an idea for future development of novel vaccines based on multi-antigens delivered by probiotic bacteria.

Evaluation of a subunit vaccine candidate (Biotech Vac Cox) against Eimeria spp. in broiler chickens

This study evaluated growth performance and cross-protection against Eimeria spp. using a subunit coccidia vaccine in 2 independent challenge experiments. In both trials, chickens were challenged with E. acervulina, E. maxima, and E. tenella oocysts. In Exp 1, 1000-day-old chickens were allocated in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 35, and 42. On d 34, coccidia lesions were scored. Oocysts per gram of feces (OPG) were evaluated on d 28, 35, and 42. In Exp 2, 900-day-old chickens were assigned in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 27, 35, and 42, and lesion scores and OPG at d 27. In Exp 1, chickens vaccinated had significantly lower feed intake (FI) at d 21 and feed conversion ratio (FCR) at d 35 compared to control chickens (P < 0.05). Vaccinated chickens showed a significant reduction (P ≤ 0.05) in OPG for E. maxima to nondetectable levels and for all coccidian species at d 42 compared to control chickens. In Exp 2, the chickens vaccinated showed a significant increase in BW, BW gain (BWG) and reduction in FCR on d 27, 35, and 42 (P ≤ 0.05). Vaccinated chickens had significantly lower (P ≤ 0.05) lesion scores for all 3 Eimeria species. Moreover, vaccinated chickens had a reduction in total OPG of 35.50% (P = 0.0739). Studies to evaluate the serological and mucosal immune response are currently being evaluated. This inactivated, orally delivered subunit vaccine offers significant cross-protection to Eimeria spp. and eliminates the needs to treat broilers with live oocysts, enhanced ease of use, and greater biosecurity to producers.

Full-length transcriptome sequence analysis of Eimeria necatrix unsporulated oocysts and sporozoites identifies genes involved in cellular invasion

Eimeria necatrix is one of the most pathogenic chicken coccidia and causes avian coccidiosis, an enteric disease of major economic importance worldwide. Eimeria parasites have complex developmental life cycles, with an exogenous phase in the environment and an endogenous phase in the chicken intestine. Oocysts excreted by chickens rapidly undergo meiosis and cell division to form eight haploid sporozoites (SZ). SZ liberated from sporocysts in the chicken intestine migrate to their preferred site of development to initiate cellular invasion. To date, almost nothing is known about the proteins that mediate parasite invasion in E. necatrix. In order to discover genes with functions involved in cellular invasion, the transcriptome profiles of E. necatrix unsporulated oocysts (UO) and SZ were analyzed using a combination of third-generation single-molecule real-time sequencing (TGS) and second-generation sequencing (SGS) followed by qRT-PCR validation. Correction of TGS long reads by SGS short reads resulted in 34,932 (UO) and 23,040 (SZ) consensus isoforms. After subsequent assembly, a total of 4949 and 4254 genes were identified from UO and SZ libraries, respectively. A total of 8376 genes were identified as differentially expressed genes (DEGs) between SZ and UO. Compared to UO, 4057 genes were upregulated and 4319 genes were downregulated in SZ. Approximately 1399 and 1758 genes were defined as stage-specific genes in SZ and UO, respectively. Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that 2978 upregulated SZ genes were clustered into 29 GO terms, and 857 upregulated SZ genes were associated with 26 KEGG pathways. We also predicted a further 50 upregulated SZ genes and 73 upregulated UO genes encoding microneme proteins, apical membrane antigens, rhoptry neck proteins, rhoptry proteins, dense granule proteins, heat shock proteins, calcium-dependent protein kinases, cyclin-dependent kinases, cGMP-dependent protein kinase, and glycosylphosphatidylinositol-anchored surface antigens. Our data reveal new features of the E. necatrix transcriptional landscape and provide resources for the development of novel vaccine candidates against E. necatrix infection.

Eimeria tenella Translation Initiation Factor eIF-5A That Interacts With Calcium-Dependent Protein Kinase 4 Is Involved in Host Cell Invasion

Eimeria tenella is an apicomplexan, parasitic protozoan known to infect poultry worldwide. An important calcium-dependent protein kinase (CDPK) has been identified in plants, green algae, ciliates and apicomplexan, such as E. tenella. CDPKs are effector molecules involved in calcium signaling pathways, which control important physiological processes such as gliding motility, reproduction, and host cell invasion. Given that CDPKs are not found in the host, studying the functions of CDPKs in E. tenella may serve as a basis for developing new therapeutic drugs and vaccines. To assess the function of CDPK4 in E. tenella (EtCDPK4), a putative interactor, translation initiation factor eIF-5A (EteIF-5A), was screened by both co-immunoprecipitation (co-IP) and His pull-down assays followed by mass spectrometry. The interaction between EteIF-5A and EtCDPK4 was determined by bimolecular fluorescence complementation (BiFC), GST pull-down, and co-IP. The molecular characteristics of EteIF-5A were then analyzed. Quantitative real-time polymerase chain reaction and western blotting were used to determine the transcription and protein levels of EteIF-5A in the different developmental stages of E. tenella. The results showed that the transcription level of EteIF-5A mRNA was highest in second-generation merozoites, and the protein expression level was highest in unsporulated oocysts. Indirect immunofluorescence showed that the EteIF-5A protein was found throughout the cytoplasm of sporozoites, but not in the refractile body. As the invasion of DF-1 cells progressed, EteIF-5A fluorescence intensity increased in trophozoites, decreased in immature schizonts, and increased in mature schizonts. The secretion assay results, analyzed by western blotting, indicated that EteIF-5A was a secreted protein but not from micronemes. The results of invasion inhibition assays showed that rabbit anti-rEteIF-5A polyclonal antibodies effectively inhibited cell invasion by sporozoites, with an inhibition rate of 48%.