Molecular characterization of a potential receptor of Eimeria acervulina microneme protein 3 from chicken duodenal epithelial cells

Identification and characterization of the receptors of a microneme adhesive repeat domain of Eimeria maxima microneme protein 3 in chicken intestine epithelial cells

Eimeria maxima microneme protein 3 (EmMIC3) is pivotal in the initial recognition and attachment of E. maxima sporozoites to host cells. EmMIC3 comprises 5 tandem Type I microneme adhesive repeat (MAR) domains, among which MAR2 of EmMIC3 (EmMAR2) has been identified as the primary determinant of EmMIC3-mediated tissue tropism. Nonetheless, the mechanisms through which EmMAR2 guides the parasite to its invasion site through interactions with host receptors remained largely uncharted. In this study, we employed yeast two-hybrid (YTH) screening assays and shotgun LC-MS/MS analysis to identify EmMAR2 receptors in chicken intestine epithelial cells. ATPase H+ transporting V1 subunit G1 (ATP6V1G1), receptor accessory protein 5 (REEP5), transmembrane p24 trafficking protein (TMED2), and delta 4-desaturase sphingolipid 1 (DEGS1) were characterized as the 4 receptors of EmMAR2 by both assays. By blocking the interaction of EmMAR2 with each receptor using specific antibodies, we observed varying levels of inhibition on the invasion of E. maxima sporozoites, and the combined usage of all 4 antibodies resulted in the most pronounced inhibitory effect. Additionally, the spatio-temporal expression profiles of ATP6V1G1, REEP5, TMED2, and DEGS1 were assessed. The tissue-specific expression patterns of EmMAR2 receptors throughout E. maxima infection suggested that ATP6V1G1 and DEGS1 might play a role in early-stage invasion, whereas TMED2 could be involved in middle and late-stage invasion and REEP5 and DEGS1 may participate primarily in late-stage invasion. Consequently, E. maxima may employ a multitude of ligand-receptor interactions to drive invasion during different stages of infection. This study marks the first report of EmMAR2 receptors at the interface between E. maxima and the host, providing insights into the invasion mechanisms of E. maxima and the pathogenesis of coccidiosis.

Host protein EPCAM interacting with EtMIC8-EGF is essential for attachment and invasion of Eimeria tenella in chickens

The five epidermal growth factor-like domains (EGF) of Eimeria tenella microneme protein 8 (EtMIC8) (EtMIC8-EGF) plays a vital role in host cell attachment and invasion. These processes require interactions between parasite proteins and receptors on the surface of host cells. In this study, five chicken membrane proteins potentially interacting with EtMIC8-EGF were identified using the GST pull-down assay and mass spectrometry analysis, and only chicken (Gallus gallus) epithelial cell adhesion molecule (EPCAM) could bind to EtMIC8-EGF. EPCAM-specific antibody and recombinant EPCAM protein (rEPCAM) inhibited the EtMIC8-EGF binding to host cells in a concentration-dependent manner. Furthermore, the rEPCAM protein showed a binding activity to sporozoites in vitro, and a significant reduction of E. tenella invasion in DF-1 cells was further observed after pre-incubation of sporozoites with rEPCAM. The specific anti-EPCAM antibody further significantly decreased weight loss, lesion score and oocyst output during E. tenella infection, displaying partial inhibition of E. tenella infection. These results indicate that chicken EPCAM is an important EtMIC8-interacting host protein involved in E. tenella-host cell adhesion and invasion. The findings will contribute to a better understanding of the role of adhesion-associated microneme proteins in E. tenella.

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.

Evaluation of the immune protective effects of rEmMIC2 and rEmMIC3 from Eimeria magna in rabbits

Eimeria magna is a common pathogen in rabbits, which results in lethargy, weight loss, diarrhea, and even death in severe cases after infection. The current method for preventing rabbit coccidiosis is to add anticoccidial drugs to the diet. However, there are many concerns about drug resistance and drug residues. In our study, the rEmMIC2 and rEmMIC3 proteins were cloned and expressed to evaluate potential as recombinant subunit vaccine candidate antigens. The protective effects of rEmMIC2 and rEmMIC3 were evaluated by the relative weight gain ratio, oocyst decrease rate, anticoccidial index, feed conversion ratio, pathological alterations, clinical symptoms, specific IgG antibody, and cytokine levels in rabbits. The molecular weights of rEmMIC2 and rEmMIC3 were 18.69 kDa and 17.47 kDa, respectively. After the coccidia challenge, the control groups showed anorexia and soft poop, whereas the experimental group showed few anorexia symptoms. Significantly different from the control group, the relative weight gain ratios of the immunized rEmMIC2 and rEmMIC3 groups were 78.37% and 75.29%, respectively, and the oocyst reduction was 77.95% and 76.09%, respectively, and the anticoccidial index was 171.12 and 169.29, respectively. IgG antibody, IFN-γ, IL-4, IL-10, and IL-17 levels were significantly increased in the experimental group. The results showed that rEmMIC2 and rEmMIC3 have potential as vaccine candidate antigens.

Designing multiepitope-based vaccine against Eimeria from immune mapped protein 1 (IMP-1) antigen using immunoinformatic approach

Drug resistance against coccidiosis has posed a significant threat to chicken welfare and productivity worldwide, putting daunting pressure on the poultry industry to reduce the use of chemoprophylactic drugs and live vaccines in poultry to treat intestinal diseases. Chicken coccidiosis, caused by an apicomplexan parasite of Eimeria spp., is a significant challenge worldwide. Due to the experience of economic loss in production and prevention of the disease, development of cost-effective vaccines or drugs that can stimulate defence against multiple Eimeria species is imperative to control coccidiosis. This study explored Eimeria immune mapped protein-1 (IMP-1) to develop a multiepitope-based vaccine against coccidiosis by identifying antigenic T-cell and B-cell epitope candidates through immunoinformatic techniques. This resulted in the design of 7 CD8⁺, 21 CD4⁺ T-cell epitopes and 6 B-cell epitopes, connected using AAY, GPGPG and KK linkers to form a vaccine construct. A Cholera Toxin B (CTB) adjuvant was attached to the N-terminal of the multiepitope construct to improve the immunogenicity of the vaccine. The designed vaccine was assessed for immunogenicity (8.59968), allergenicity and physiochemical parameters, which revealed the construct molecular weight of 73.25 kDa, theoretical pI of 8.23 and instability index of 33.40. Molecular docking simulation of vaccine with TLR-5 with binding affinity of - 151.893 kcal/mol revealed good structural interaction and stability of protein structure of vaccine construct. The designed vaccine predicts the induction of immunity and boosted host's immune system through production of antibodies and cytokines, vital in hindering surface entry of parasites into host. This is a very important step in vaccine development though further experimental study is still required to validate these results.

Eimeria acervulina Microneme Protein 3 Inhibits Apoptosis of the Chicken Duodenal Epithelial Cell by Targeting the Casitas B-Lineage Lymphoma Protein

Eimeria acervulina (E. acervulina) causes coccidiosis in poultry which persists as economic pain worldwide. Most damage to the intestinal mucosa results from apoptosis of the infected intestinal epithelial cells. The Microneme protein 3 (MIC3) protein is a key virulence factor in some parasites involved in host cell apoptosis inhibition. Here, we studied whether and how MIC3 affects the apoptosis in E. acervulina infected chicken duodenal epithelial cells. Through flow cytometry (FCM), we found that the presence of merozoites and the overexpression of MIC3 significantly decreased apoptosis and the activity of caspase-3 in chicken duodenal epithelial cells at 4, 6, and 8 h post merozoite infection (P < 0.01). Silencing the Casitas B-lineage lymphoma (CBL) protein, a host receptor for MIC3 with shRNA was shown to promote apoptosis in the chicken duodenal epithelial cells. The early apoptotic rate of host cells in the lentiviral-MIC3 group was significantly lower than that in the lentiviral-MIC3 + shRNA CBL group at 4 h after MIC3 expression (P < 0.01), and it was moderately decreased in the lentiviral-MIC3 + shRNA CBL group compared with that in the shRNA CBL group. Our data indicated that MIC3 inhibited early apoptosis of E. acervulina infected chicken duodenal epithelial cells by targeting host receptor-CBL protein. These findings unveiled one of the mechanisms of how intracellular parasites affect the apoptosis of infected host cells, which provided a deeper understanding of their pathogenesis.