Identification of a fibronectin-like molecule on Eimeria tenella

EXPRESSION OF FLOTILLIN-1 ON EIMERIA TENELLA SPOROZOITES AND ITS ROLE IN HOST CELL INVASION

Lipid rafts are detergent-resistant, liquid-ordered microdomains in plasma membranes that are enriched in cholesterol and sphingolipids and involved in intracellular signal transduction, membrane trafficking, and molecular sorting. In this study, we investigated the possibility that lipid rafts on Eimeria tenella sporozoites may act as platforms for host cell invasion. Flotillin-1, a resident protein of lipid rafts, was identified on E. tenella sporozoites and was prominently expressed at the apex of the cells, a region mediating host cell invasion. Pretreatment of sporozoites with antibody against flotillin-1 blocked parasite invasion. Furthermore, the anticoccidial drug, monensin, disrupted the localization of flotillin-1 within raft structures resulting in loss of invasion. We conclude that Eimeria sporozoites utilize lipid rafts containing flotillin-1 for internalization into host cells.

A "chimera" theory on the origin of dicyemid mesozoans: evolution driven by frequent lateral gene transfer from host to parasite

The phylogenetic status of the enigmatic dicyemid mesozoans is still uncertain. Are they primitive multicellular organisms or degenerate triploblastic animals? Presently, the latter view is accepted. A phylogenetic analysis of 18S rDNA sequences placed dicyemids within the animal clade, and this was supported by the discovery of a Hox-type gene with a lophotrochozoan signature sequence. This molecular information suggests that dicyemid mesozoans evolved from an ancestral animal degenerately. Considering their extreme simplicity, which is probably due to parasitism, they might have come from an early embryo via a radical transformation, i.e. neoteny. Irrespective of this molecular information, dicyemid mesozoans retain many protistan-like or extremely primitive features, such as tubular mitochondrial cristae, endocytic ability from the outer surface, and the absence of collagenous tissue, while they do not share noticeable synapomorphy with animals. In addition, the 5S rRNA phylogeny suggests a somewhat closer kinship with protozoan ciliates than with animals. If we accept this clear contradiction, dicyemids should be regarded as a chimera of animals and protistans. Here, we discuss the traditional theory of extreme degeneration via parasitism, and then propose a new "chimera" theory in which dicyemid mesozoans are exposed to a continual flow of genetic information via eating host tissues from the outer surface by endocytosis. Consequently, many of their intrinsic genes have been replaced by host-derived genes through lateral gene transfer (LGT), implying that LGT is a key driving force in the evolution of dicyemid mesozoans.

Involvement of alpha(v)beta3 integrin-like receptor and glycosaminoglycans in Candida albicans germ tube adhesion to vitronectin and to a human endothelial cell line

The present study was undertaken to investigate the expression of alpha(v)beta3 and alpha(v)beta5 integrin-like vitronectin receptors (VNRs) on Candida albicans germ tube and their involvement in its adhesion to vitronectin (VN) and human endothelial cells. By immunofluorescence and FACS analysis, several monoclonal antibodies directed against human alpha(v) or beta3 integrin subunit or alpha(v)beta3 and alpha(v)beta5 heterodimers, positively stained C. albicans germ tubes. C. albicans germ tubes specifically adhered (45-50%) to VN and this adhesion was markedly inhibited by RGD-, but not RGE-containing peptides. Adhesion of C. albicans germ tubes to VN was strongly inhibited by anti-alphav, anti-beta3 or anti-alpha(v)beta3, but not by alpha(v)beta5 monoclonal antibody. C. albicans germ tube adhesion to VN was also inhibited by glycosaminoglycans (GAGs) such as heparin or chondroitin sulphate. Finally, we show that C. albicans germ tubes adhere to the human EA.hy 926 endothelial cell line. This adhesion is markedly blocked by anti-beta3 monoclonal antibody, GRGDSP peptide or heparin, and is completely abolished by their combination. Overall these results indicate that C. albicans germ tube adherence to VN and to a human endothelial cell line is mediated by alpha(v)beta3, but not by alpha(v)beta5-like integrin, and depends on GAGs which may act by regulating alpha(v)beta3 integrin-like/VN adhesive interaction.

Eimeria necatrix virus: intracellular localisation of viral particles and proteins

The presence of the Eimeria necatrix virus was investigated in the following life cycle stages: sporocysts, sporozoites, merozoites, and macrogametes. Electron microscopy revealed virus-like particles (VLPs) in sporozoites, which were purified from sporozoite extracts and used to raise polyclonal antibodies. Viral proteins were identified as RNA polymerase (95 kDa) and the major capsid protein (80 kDa). Polyclonal antibody was used to detect the intracellular localisation of VLPs and proteins. Immunoelectron microscopy and immunohistochemistry identified a viral protein of 95 kDa in all the E. necatrix stages studied, whereas the 80 kDa protein was found only in sporocysts and sporozoites. In addition, no VLPs were found in sporocysts. These results indicate that the synthesis of viral capsid proteins takes place during the early events of sporulation, and is then packaged into novel viruses during the late events. No VLPs were seen and no capsid proteins were found in the merozoites and macrogametes, whereas the 95 kDa RNA polymerase was present in both these stages. In addition, no VLPs or proteins were detected in chicken tissues.

Development and use of monoclonal antibodies to chicken fibronectin to show that the chicken hepatocellular carcinoma cell line, LMH, constitutively expresses fibronectin

Fibronectin (Fn) is a high molecular weight glycoprotein and acute phase reactant that contributes to a variety of cellular activities including proliferation and wound healing. Production of Fn is influenced by cytokines such as IL-1alpha, IL-6 and TNF -alpha, and in serum Fn levels can function as an indicator of sepsis and reticulo-endothelial function. Here we describe the production of a panel of mAb to chicken Fn and give evidence that a chicken hepatocellular carcinoma cell line, LMH, constitutively expresses Fn. A capture ELISA to measure chicken Fn was developed using an IgG1 mAb (AV62) as the capture Ab, and biotinylated AV63 (IgG2b) as the detecting Ab. This study identified a single commercially available mAb directed against human Fn that also recognised chicken Fn. By contrast, the anti-chicken Fn mAbs did not cross-react with either human or bovine Fn.

Immunohistochemical study of S100-like protein in Eimeria brunetti and Eimeria acervulina

We have investigated the expression of a calcium-binding protein, the S100 protein, in Eimeria brunetti and Eimeria acervulina stages. For this purpose, paraffin sections of distal ileum and bursa of Fabricius or duodenum from experimentally infected chickens were treated with anti-alpha-S100 (anti-alpha subunit of S100 protein) and anti-beta-S100 (anti-beta subunit of S100 protein) monoclonal antibodies and anti-S100 whole molecule polyclonal antibody. The avidin-biotin peroxidase method was used to demonstrate immunoreactivity. In the ileum, our results reveal a positive immunoreaction for the beta subunit and S100 whole molecule within the macrogametes of E. brunetti, whereas they were devoid of immunostaining after treatment of the paraffin sections with the anti-alpha-S100 antiserum. Schizonts and oocysts of E. brunetti and all the E. acervulina stages gave a negative reaction after treatment with any of the three antiserum used in the study. This result indicated that the S100 protein molecules within these stages were not recognized by the antibodies, suggesting that these molecules are different from those identified in macrogametes of E. brunetti. By contrast, in the epithelial cells, lining the lumen of the bursa of Fabricius, macrogametes of E. brunetti were stained by the three antibodies used. These results may indicate the existence of metabolic adaptations that enable the parasite to invade tissue sites different from those where the parasite usually develops.

Progress in recombinant vaccine development against coccidiosis. A review and prospects into the next millennium

The increasing problems encountered by the poultry industry, despite the extensive use of drugs, have emphasised the need for an immunological solution for the economic damage caused by the Eimeria parasite. Although immunity develops relatively fast following a natural infection, to induce protection by using parasite extracts or single antigens appears more difficult. Nevertheless, the development of a vaccine based on defined antigens seems the best solution in the long run. At the VIth International Coccidiosis Conference in 1993 the first promising results were reported from small-scale experiments using recombinant antigens. This review summarises the advances in this field of research from 1993 onwards. Although since then not many reports have been published about the effects of using recombinant. antigens as a vaccine against coccidiosis, a number of interesting new proteins which could be considered good targets for such a vaccine have been described and are referred to herein. Proteins involved in the process of invasion of the host cell by the extracellular parasite are regarded as key components in the developmental cycle of the parasite. These components possibly bind to receptors on the host cell. Interference with this process could be a target of the protective immune response. Progress has also been made in characterising the immune mechanisms activated by infection with the parasite. From experimental mouse models and from studies in chickens, a better insight has been obtained towards the involvement of CD4- and CD8-type T cells in, respectively, the inductor and the effector branch of the immune response, although not all questions have been answered. Several antigens have been selected using T-cell stimulation and cytokine assays and these are reviewed. In a third section, mostly unpublished results of our own experiments dealing with the use of live vectors to present defined antigens such as Ea1A and EaSC2, a parasite refractile body transhydrogenase and a lactate dehydrogenase, respectively, are summarised. Partial protection could be induced using Salmonella typhimurium as a carrier for these antigens, in that the oocyst output was reduced by up to 50% after challenge and weight gain could be improved by 5-10% over non-vaccinated challenged chickens, when tested in a floor-pen trial. Similar results were obtained when these antigens were presented by viral vectors such as Fowlpox virus or Herpes virus of turkey. These data seem to offer good prospects for the accomplishment of a safe and efficaceous vaccine based on recombinant DNA technology. These expectations are corroborated by recent breakthrough in transfection of related parasites such as Plasmodium and Toxoplasma gondii, and by the increasing amount of genomic information becoming available every day, the impact of which cannot even be estimated yet. These new technologies will allow us to solve the complex problems that we once created ourselves.