Production of a monoclonal antibody against a mannose-binding protein of Acanthamoeba culbertsoni and its localization

Acanthamoeba Mannose and Laminin Binding Proteins Variation across Species and Genotypes

Acanthamoeba is a ubiquitous free-living amoeba capable of being an opportunistic pathogen in humans and animals. A critical step in infection is the adhesion of the amoeba to host cells and tissues, and two major parasite adhesins, mannose-binding protein (MBP) and laminin-binding protein (LBP), are known to recognize the cell surface glycoproteins and those of the extracellular matrix, respectively. In this study, the available genomes of Acanthamoeba were analysed to recover the sequences of MBP and LBP using previously published genetic data. Genes for both proteins were successfully obtained from strains belonging to various genotypes (T4A, T4D, T4G, T4F, T2, T5, T10, T22, T7 and T18), resulting in a single gene for LBP but identifying two types of MBP, MBP1 and MBP2. Phylogenetic analysis based on deduced amino acid sequences shows that both MBP and LBP have a branching pattern that is consistent with that based on 18S rDNA, indicating that changes in both proteins occurred during diversification of Acanthamoeba lines. Notably, all MBPs possess a conserved motif, shared with some bacterial C-type lectins, which could be the recognition site for mannose binding.

Detection of Acanthamoeba from Acanthamoeba Keratitis Mouse Model Using Acanthamoeba-Specific Antibodies

Although the prevalence of Acanthamoeba keratitis (AK) is rare, its incidence in contact lens wearers has increased. Acanthamoeba infections can lead to the loss of vision if the diagnosis and treatment are delayed. In this study, we investigated the diagnostic potential of two antibodies raised against the adenylyl cyclase-associated protein (ACAP) and periplasmic binding protein (PBP) of A. castellanii in the AK mouse model. The specificity of ACAP and PBP antibodies to Acanthamoeba was confirmed by immunocytochemistry. AK mouse models were produced by corneal infections with A. castellanii trophozoites for 7 days and 21 days. Enzyme-linked immunosorbent assay results revealed that both ACAP and PBP antibodies successfully detected Acanthamoeba antigens in the tears and eyeball lysates of the AK mouse model. The detection levels of Acanthamoeba antigens were similar at both infection time points. Anti-Acanthamoeba IgG, IgA, and IgM antibodies were evaluated from the sera of the AK mouse model. Notably, IgM and IgA antibody responses were highest and lowest at both time points, respectively. Our findings revealed that both ACAP and PBP antibodies could detect Acanthamoeba antigens in the tears and eyeball lysates of the AK mouse model. These results provide important information for understanding Acanthamoeba infections and developing a new diagnostic tool for AK.

Specific Detection of Acanthamoeba species using Polyclonal Peptide Antibody Targeting the Periplasmic Binding Protein of A. castellanii

Acanthamoeba keratitis (AK) is a rare ocular disease, but it is a painful and sight-threatening infectious disease. Early diagnosis and adequate treatment are necessary to prevent serious complications. While AK is frequently diagnosis via several PCR assays or Acanthamoeba-specific antibodies, a more specific and effective diagnostic method is required. This study described the production of a polyclonal peptide antibody against the periplasmic binding protein (PBP) of A. castellanii and investigated its diagnostic potential. Western blot analysis showed that the PBP antibody specifically reacted with the cell lysates of A. castellanii. However, the PBP antibody did not interact with human corneal epithelial (HCE) cells and the other 3 major causative agents of keratitis. Immunocytochemistry (ICC) results revealed the specific detection of A. castellanii trophozoites and cysts by PBP antibodies when A. castellanii were co-cultured with HCE cells. PBP antibody specificity was further confirmed by co-culture of A. castellanii trophozoites with F. solani, S. aureus, and P. aeruginosa via ICC. The PBP antibody specifically reacted with the trophozoites and cysts of A. polyphaga, A. hatchetti, A. culbertsoni, A. royreba, and A. healyi, thus demonstrated its genus-specific nature. These results showed that the PBP polyclonal peptide antibody of A. castellanii could specifically detect several species of Acanthamoeba, contributing to the development of an effective antibody-based AK diagnostics.

Characterization of a Peptide Antibody Specific to the Adenylyl Cyclase-Associated Protein of Acanthamoeba castellanii

Acanthamoeba keratitis (AK) is a rare infectious disease and accurate diagnosis has remained arduous as clinical manifestations of AK were similar to keratitis of viral, bacterial, or fungal origins. In this study, we described the production of a polyclonal peptide antibody against the adenylyl cyclase-associated protein (ACAP) of A. castellanii, and evaluated its differential diagnostic potential. Enzyme-linked immunosorbent assay revealed high titers of A. castellanii-specific IgG and IgA antibodies being present in low dilutions of immunized rabbit serum. Western blot analysis revealed that the ACAP antibody specifically interacted with A. castellanii, while not interacting with human corneal epithelial (HCE) cells and other causes of keratitis such as Fusarium solani, Pseudomonas aeruginosa, and Staphylococcus aureus. Immunocytochemistry (ICC) results confirmed the specific detection of trophozoites and cysts of A. castellanii co-cultured with HCE cells. The ACAP antibody also specifically interacted with the trophozoites and cysts of 5 other Acanthamoeba species. These results indicate that the ACAP antibody of A. castellanii can specifically detect multiple AK-causing members belonging to the genus Acanthamoeba and may be useful for differentially diagnosing Acanthamoeba infections.

Various brain-eating amoebae: the protozoa, the pathogenesis, and the disease

Among various genera of free-living amoebae prevalent in nature, some members are identified as causative agents of human encephalitis, in which Naegleria fowleri followed by Acanthamoeba spp. and Balamuthia mandrillaris have been successively discovered. As the three dominant genera responsible for infections, Acanthamoeba and Balamuthia work as opportunistic pathogens of granulomatous amoebic encephalitis in immunocompetent and immunocompromised individuals, whereas Naegleria induces primary amoebic meningoencephalitis mostly in healthy children and young adults as a more violent and deadly disease. Due to the lack of typical symptoms and laboratory findings, all these amoebic encephalitic diseases are difficult to diagnose. Considering that subsequent therapies are also affected, all these brain infections cause significant mortality worldwide, with more than 90% of the cases being fatal. Along with global warming and population explosion, expanding areas of human and amoebae activity in some regions lead to increased contact, resulting in more serious infections and drawing increased public attention. In this review, we summarize the present information of these pathogenic free-living amoebae, including their phylogeny, classification, biology, and ecology. The mechanisms of pathogenesis, immunology, pathophysiology, clinical manifestations, epidemiology, diagnosis, and therapies are also discussed.

Production of a monoclonal antibody against a galactose-binding protein of Acanthamoeba castellanii and its cytotoxicity

In this study, it was confirmed whether the galactose-binding protein (GBP) was present in Acanthamoeba castellanii, and its function on a target cell was confirmed by production of an antibody against the GBP. Since the genes for GBP have not yet been identified at all, the purification of GBP was done using galactose-beads from amoebial lysates, and monoclonal antibodies were produced using cell fusion. GBP was confirmed to have a size of about 35 kDa. After the third immunization with purified GBP in BALB/c mice, monoclonal antibody production was analyzed. The clone cultured before limiting dilution was named 2AB2 and showed the highest antibody titer in the culture supernatant of a 24-well plate. AF6 clone cultured after limiting dilution showed an antibody titer of 0.259 in a 75-T flask. Antibodies generated by collecting ascites by injecting monoclonal colonies into the abdominal cavity of mice were confirmed through gel analysis and were observed to belong to the isotype of the IgM having kappa chains. Since the cytotoxicity of A. castellanii was inhibited by about 26% by the monoclonal antibody against GBP, it was confirmed that the antibody against GBP had an inhibitory effect on cytotoxicity. This study was the first report on GBP isolated and purified from A. castellanii, and similarly to a mannose-binding protein (MBP), its involvement in contact-dependent cytotoxicity was demonstrated with monoclonal antibody production.

Chorismate mutase peptide antibody enables specific detection of Acanthamoeba

Accurate and rapid diagnosis of Acanthamoeba keratitis (AK) is difficult. Although the diagnostic procedure for AK has improved, further development and effective diagnostic tool utilization for AK need to continue. Chorismate mutase is a key regulatory enzyme involved in the shikimate pathway, a metabolic pathway absent in mammals but central for amino acid biosynthesis in bacteria, fungi, algae, and plants. In this study, we describe the identification and production of a polyclonal peptide antibody targeting chorismate mutase secreted by A. castellanii, which could be used for AK diagnosis. Western blot was performed using the protein lysates and conditioned media of the human corneal epithelial (HCE) cells, non-pathogenic Acanthamoeba, pathogenic Acanthamoeba, clinical isolate of Acanthamoeba spp., and other causes of keratitis such as Fusarium solani, Pseudomonas aeruginosa, and Staphylococcus aureus. Polyclonal antibodies raised against A. castellanii chorismate mutase specifically interacted with lysates of Acanthamoeba origin and their culture media, while such interactions were not observed from other samples. Acanthamoeba-specificity of chorismate mutase was also confirmed using immunocytochemistry after co-culturing Acanthamoeba with HCE cells. Specific binding of the chorismate mutase antibody to Acanthamoeba was observed, which were absent in the case of HCE cells. These results indicate that the chorismate mutase antibody of Acanthamoeba may serve as a method for rapid and differential Acanthamoeba identification.

Interactions Between Acanthamoeba culbertsoni and Pathogenic Bacteria and their Inhibition by Lectin-Antibodies

In this study, using pathogenic and non-pathogenic bacteria, it was analyzed whether a polyclonal serum and a monoclonal antibody to A. culbertsoni mannose-binding protein (MBP) could inhibit its interaction. The association of the amoeba with E. coli O157:H7 was very strong at a level of over 100%, but the non-pathogenic E. coli strain was about five times lower at 22%. Pathogenic K. pnueumoniae also showed high association with amoeba by about 92% as compared with pathogenic E. coli O157:H7 and S. agalactiae. The polyclonal serum to MBP inhibited E. coli O157:H7 association to amoeba 2.5 times more than untreated E. coli O157:H7. Monoclonal antibody to MBP also inhibited bacterial association with amoeba but was not stronger than the polyclonal serum. Pathogenic E. coli O157:H7 showed about 88% invasion into amoeba and decreased about 22% as compared with associated E. coli O157:H7. Polyclonal serum to MBP inhibited about 55%, 50%, and 44% in E. coli O157:H7, K. pneumoniae and S. agalactiae, respectively. The invasion of K. pneumoniae and S. agalactiae was not high as polyclonal serum but was about 8% to 10% weaker than polyclonal serum. The pathogenic strains of K. pneumoniae and S. agalactiae showed less decrease in survival as shown at invasion than E. coli O157:H7 without antibody. This study provided the information that the pathogenic bacteria could be more interactive with A. culbertsoni trophozoites as a reservoir host than non-pathogenic E. coli, and the amoeba should interact with bacteria by the MBP lectin.

Production of a polyclonal antibody against inosine-uridine preferring nucleoside hydrolase of Acanthamoeba castellanii and its access to diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a rare disease but its prevalence throughout the globe continues to grow, primarily due to increased contact lens usage. Since early-stage symptoms associated with AK closely resemble those from other corneal infections, accurate diagnosis is difficult and this often results in delayed treatment and exacerbation of the disease, which can lead to permanent visual impairment. Accordingly, developing a rapid Acanthamoeba–specific diagnostic method is highly desired. In the present study, a rapid and differential method for AK diagnosis was developed using the secretory proteins derived from the pathogenic Acanthamoeba. Among the vast quantities of proteins secreted by the pathogenic Acanthamoeba, an open reading frame of the inosine-uridine preferring nucleoside hydrolase (IPNH) gene was obtained. After expressing and purifying the IPNH protein using the pGEX 4T-3 vector system, mice were immunized with the purified proteins for polyclonal antibody generation. Western blot was performed using protein lysates of the human corneal cell, non-pathogenic amoeba, pathogenic amoeba, and clinical amoeba isolate along with lysates from other causes of keratitis such as Staphylococcus aureus, Pseudomonas aeruginosa, and Fusarium solani to confirm Acanthamoeba-specificity. Western blot using the polyclonal IPNH antibody revealed that IPNH was Acanthamoeba-specific since these proteins were only observed in lysates of Acanthamoeba origin or its culture media. Our findings indicate that the IPNH antibody of Acanthamoeba may serve as a potential agent for rapid and differential AK diagnosis.

Acanthamoeba spp. monoclonal antibody against a CPA2 transporter: a promising molecular tool for acanthamoebiasis diagnosis and encystment study

Free-living amoeba of the genus Acanthamoeba are ubiquitous protozoa involved in opportunistic and non-opportunistic infection in humans, such as granulomatous amoebic encephalitis and amoebic keratitis. Both infections have challenging characteristics such as the formation of the resistant cysts in infected tissues, hampering the treatment and most usual diagnosis depending on time-consuming and/or low sensitivity techniques. The use of monoclonal antibodies presents itself as an opportunity for the development of more effective alternative diagnostic methods, as well as an important and useful tool in the search for new therapeutic targets. This study investigated the possibility of using a previously produced monoclonal antibody (mAb3), as a diagnostic tool for the detection of Acanthamoeba trophozoites by direct and indirect flow cytometry and immunofluorescence. Immunoprecipitation assay and mass spectrometry allowed the isolation of the antibody's target and suggested it is a transporter part of the CPA (cation: proton antiporter) superfamily. In vitro tests indicate an important role of this target in Acanthamoeba's encystment physiology. Our results support the importance of studying the role of CPA2 transporters in the context of acanthamoebiasis, as this may be a way to identify new therapeutic candidates.

The most abundant cyst wall proteins of Acanthamoeba castellanii are lectins that bind cellulose and localize to distinct structures in developing and mature cyst walls

Background

Acanthamoeba castellanii, which causes keratitis and blindness in under-resourced countries, is an emerging pathogen worldwide, because of its association with contact lens use. The wall makes cysts resistant to sterilizing reagents in lens solutions and to antibiotics applied to the eye.

Methodology/Principal findings

Transmission electron microscopy and structured illumination microscopy (SIM) showed purified cyst walls of A. castellanii retained an outer ectocyst layer, an inner endocyst layer, and conical ostioles that connect them. Mass spectrometry showed candidate cyst wall proteins were dominated by three families of lectins (named here Jonah, Luke, and Leo), which bound well to cellulose and less well to chitin. An abundant Jonah lectin, which has one choice-of-anchor A (CAA) domain, was made early during encystation and localized to the ectocyst layer of cyst walls. An abundant Luke lectin, which has two carbohydrate-binding modules (CBM49), outlined small, flat ostioles in a single-layered primordial wall and localized to the endocyst layer and ostioles of mature walls. An abundant Leo lectin, which has two unique domains with eight Cys residues each (8-Cys), localized to the endocyst layer and ostioles. The Jonah lectin and glycopolymers, to which it binds, were accessible in the ectocyst layer. In contrast, Luke and Leo lectins and the glycopolymers, to which they bind, were mostly inaccessible in the endocyst layer and ostioles.

Conclusions/Significance

The most abundant A. castellanii cyst wall proteins are three sets of lectins, which have carbohydrate-binding modules that are conserved (CBM49s of Luke), newly characterized (CAA of Jonah), or unique to Acanthamoebae (8-Cys of Leo). Cyst wall formation is a tightly choreographed event, in which lectins and glycopolymers combine to form a mature wall with a protected endocyst layer. Because of its accessibility in the ectocyst layer, an abundant Jonah lectin is an excellent diagnostic target.

A half century ago, investigators identified cellulose in the Acanthamoeba cyst wall, which has two layers and conical ostioles that connect them. Here we showed cyst walls contain three large sets of cellulose-binding lectins, which localize to the ectocyst layer (a Jonah lectin) or to the endocyst layer and ostioles (Luke and Leo lectins). We used the lectins to establish a sequence for cyst wall assembly when trophozoites are starved and encyst. In the first stage, a Jonah lectin and glycopolymers were present in dozens of distinct vesicles. In the second stage, a primordial wall contained small, flat ostioles outlined by a Luke lectin. In the third stage, a Jonah lectin remained in the ectocyst layer, while Luke and Leo lectins moved to the endocyst layer and ostioles. A description of the major events during cyst wall development is a starting point for mechanistic studies of its assembly.