Immunoglobulin constant regions provide stabilization to the paratope and enforce epitope specificity.

Constant domains in antibody molecules at the level of the Fab (CH1 and CL) have long been considered to be simple scaffolding elements that physically separate the paratope-defining variable (V) region from the effector function-mediating constant (C) regions. However, due to recent findings that C domains of different isotypes can modulate the fine specificity encoded in the V region, elucidating the role of C domains in shaping the paratope and influencing specificity is a critical area of interest. To dissect the relative contributions of each C domain to this phenomenon, we generated antibody fragments with different C regions omitted, using a set of antibodies targeting capsular polysaccharides from the fungal pathogen, Cryptococcus neoformans. Antigen specificity mapping and functional activity measurements revealed that V region-only antibody fragments exhibited poly-specificity to antigenic variants and extended to recognition of self-antigens, while measurable hydrolytic activity of the capsule was greatly attenuated. To better understand the mechanistic origins of the remarkable loss of specificity that accompanies the removal of C domains from identical paratopes, we performed molecular dynamics simulations which revealed increased paratope plasticity in the scFv relative to the corresponding Fab. Together, our results provide insight into how the remarkable specificity of immunoglobulins is governed and maintained at the level of the Fab through the enforcement of structural restrictions on the paratope by CH1 domains.

Antibody-guided in vivo imaging of Aspergillus fumigatus lung infections during antifungal azole treatment.

Invasive pulmonary aspergillosis (IPA) is a life-threatening lung disease of immunocompromised humans, caused by the opportunistic fungal pathogen Aspergillus fumigatus. Inadequacies in current diagnostic procedures mean that early diagnosis of the disease, critical to patient survival, remains a major clinical challenge, and is leading to the empiric use of antifungal drugs and emergence of azole resistance. A non-invasive procedure that allows both unambiguous detection of IPA and its response to azole treatment is therefore needed. Here, we show that a humanised Aspergillus-specific monoclonal antibody, dual labelled with a radionuclide and fluorophore, can be used in immunoPET/MRI in vivo in a neutropenic mouse model and 3D light sheet fluorescence microscopy ex vivo in the infected mouse lungs to quantify early A. fumigatus lung infections and to monitor the efficacy of azole therapy. Our antibody-guided approach reveals that early drug intervention is critical to prevent complete invasion of the lungs by the fungus, and demonstrates the power of molecular imaging as a non-invasive procedure for tracking IPA in vivo.

Peptidorhamanomannan: A surface fungal glycoconjugate from Scedosporium aurantiacum and Scedosporium minutisporum and its recognition by macrophages.

The genus Scedosporium is composed of clinically relevant fungal species, such as Scedosporium aurantiacum, Scedosporium apiospermum, and Scedosporium boydii. Surface molecules have been described that play crucial roles in fungi-macrophage interaction, and many of them are pathogen-associated molecular patterns (PAMPs). The present study aims to characterize peptidoglycans obtained from Scedosporium aurantiacum and Scedosporium minutisporum, a clinical and an environmental isolate, respectively, and compare their roles in pathogen-host interaction. Both molecules were characterized as peptidorhamnomannans (PRMs), similar to what has been already described for other Scedosporium species. Rabbit immune sera obtained by injecting whole cells from each species recognized both fungal cells and purified PRMs, suggesting that a cross-reaction occur between both fungi. Immunofluorescent microscopy revealed that PRMs are exposed on fungal surface. Prior incubation of purified molecules with immune sera before adding to cells led to loss of fluorescent, indicating that PRM is a major molecule recognized by immune sera. Fungi-macrophage interaction revealed that S. aurantiacum is able to survive more inside phagocytic cells than S. minutisporum, and PRM from both fungi plays a role in phagocytosis when the purified molecule is pre-incubated with macrophage. In addition, PRM induce nitric oxide release by macrophages. Our data indicate that PRM is an important PAMP exposed on fungal surface with the potential of immune modulation.

In this work, peptidorhamnomannans from Scedosporium aurantiacum and Scedosporium minutisporum have been characterized. These molecules play important roles in phagocytosis and oxidative burst in peritoneal macrophages and are recognized by immune sera.

Characterization of an Uncinocarpus reesii-expressed recombinant tube precipitin antigen of Coccidioides posadasii for serodiagnosis.

Early and accurate diagnosis of coccidioidomycosis, also known as Valley fever, is critical for appropriate disease treatment and management. Current serodiagnosis is based on the detection of patient serum antibodies that react with tube precipitin (TP) and complement fixation (CF) antigens of Coccidioides. IgM is the first class of antibodies produced by hosts in response to coccidioidal insults. The highly glycosylated ß-glucosidase 2 (BGL2) is a major active component of the TP antigen that stimulates IgM antibody responses during early Coccidioides infection. The predominant IgM epitope on BGL2 is a unique 3-O-methyl-mannose moiety that is not produced by commonly used protein expression systems. We genetically engineered and expressed a recombinant BGL2 (rBGL2ur), derived from Coccidioides, in non-pathogenic Uncinocarpus reesii, a fungus phylogenetically related to the Coccidioides pathogen. The rBGL2ur protein was purified from the culture medium of transformed U. reesii by nickel affinity chromatography, and the presence of 3-O-methyl mannose was demonstrated by gas chromatography. Seroreactivity of the purified rBGL2ur protein was tested by enzyme-linked immunosorbent assays using sera from 90 patients with coccidioidomycosis and 134 control individuals. The sensitivity and specificity of the assay with rBGL2ur were 78.8% and 87.3%, respectively. These results were comparable to those obtained using a proprietary MiraVista Diagnostic (MVD) IgM (63.3% sensitivity; 96.3% specificity), but significantly better than the ID-TP assay using non-concentrated patient sera (33.3% sensitivity; 100% specificity). Expression of rBGL2ur in U. reesii retains its antigenicity for coccidioidomycosis serodiagnosis and greatly reduces biosafety concerns for antigen production, as Coccidioides spp. are biological safety level 3 agents.

Self-Assembly of Antigen Proteins into Nanowires Greatly Enhances the Binding Affinity for High-Efficiency Target Capture.

High-efficiency target capture is an essential prerequisite for sensitive immunoassays. However, the current available immunoassay approaches are subject to deficient binding affinities between predator-prey molecules that greatly restrict the target capture efficiency and immunoassay sensitivity. Herein, we present a new strategy through the self-assembly of antigen proteins into nanowires to enhance the binding affinity between an antigen and antibody. Through the genetic fusion of antigen proteins (e.g., HIV p24) with the yeast amyloid protein Sup35 self-assembly domain, specific antigen nanowires (Ag nanowires) were constructed and demonstrated a remarkable enhancement in binding affinity compared with that of the monomeric antigen molecule. The Ag nanowires were further combined with magnetic beads to form a 3D magnetic probe based on a seed-induced self-assembly strategy. Taking advantage of both the strong binding affinity and the rapid magnetic separation and enrichment capacity, the specific 3D magnetic probe achieved a 100-fold improvement in detection sensitivity within a significantly shorter period of 20 min over that of the conventional enzyme-linked immunosorbent assay method.

Serological proteomic biomarkers to identify Paracoccidioides species and risk of relapse.

The sensitivity of the double agar gel immunodiffusion test is about 90% in patients with untreated paracoccidioidomycosis (PCM), but it is much lower in cases of relapse. In addition, serum from patients with PCM caused by Paracoccidioides lutzii, frequent in the Midwest region of Brazil, do not react with the classical antigen obtained from Pb B-339. These findings showed the need for alternative diagnostic methods, such as biological markers through proteomics. The aim of this study was to identify biomarkers for the safe identification of PCM relapse and specific proteins that could distinguish infections caused by Paracoccidioides brasiliensis from those produced by Paracoccidioides lutzii. Proteomic analysis was performed in serum from 9 patients with PCM caused by P. brasiliensis, with and without relapse, from 4 patients with PCM produced by P. lutzii, and from 3 healthy controls. The comparative evaluation of the 29 identified plasma proteins suggested that the presence of the immunoglobulin (Ig) alpha-2 chain C region and the absence of Ig heavy chain V-III TIL indicate infection by P. lutzii. In addition, the absence of complement factor B protein might be a predictor of relapse. The evaluation of these proteins in a higher number of patients should be carried out in order to validate these findings.

PRODUCTION OF SINGLE CHAIN FRAGMENT VARIABLE (scFv) ANTIBODY AGAINST PARANOSEMA LOCUSTAE ALPHA/BETA-HYDROLASE AND IMMUNOLOCALIZATION OF MICROSPORIDIAN ENZYME IN THE INFECTED HOST CELL.

Microsporidia is a widespread group of fungi-related intracellular parasites. Direct contact of the most microsporidia species with host cytoplasm suggests that these parasites may control physiological processes of infected cells by secretion of various proteins. In previous experiments, secretion of significant amounts of microsporidia Paranosema locustae alpha/beta-hydrolase into infected cells of Locusta migratoria fat bodies was demonstrated using polyclonal antibodies against the enzyme. However, heterologous expression of microsporidian hydrolase in yeast Pichia pastoris cells was not accompanied by its secretion. In this study, we have constructed library of recombinant single chain antibodies (scFv-fragments) against proteins of fat bodies of infected locusts and isolated mini-antibody specifically recognizing the studied enzyme using phage display technology. Immunoblotting and immunofluorescent microscopy with selected scFv-fragment confirmed secretion of two different in size forms of P. locustae alpha/beta-hydrolase into infected host cell. Prospects of scFv-fragment use to explore the role of microsporidian hydrolase in host-parasite relations and mechanism of its secretion are discussed in the paper.

Novel nanoscale bacteriophage-based single-domain antibodies for the therapy of systemic infection caused by Candida albicans.

Candida albicans (C. albicans) is an important human commensal and opportunistic fungal pathogen. Secreted aspartyl proteinases (Saps) are a major virulence trait of C. albicans, and among these proteases Sap2 has the highest expression levels. It is possible that antibodies against Sap2 could provide an antifungal effect. In this study, two phages displaying anti-rSap2 single chain variable fragments (scFvs) were screened from human single fold scFv libraries, and their potential therapeutic roles were evaluated using a murine model infected by C. albicans. The in vivo efficacies were assessed by mortality rates, fungal burden and histological examination. Overall survival rates were significantly increased while the colony counts and infectious foci were significantly decreased after treatment with the scFv-phages relative to the control groups. In order to investigate the immune response provoked by scFv-phages, three kinds of cytokines (Th1, Th2 and Th17 types) were measured and a clear immune response was observed. These findings suggest that anti-rSap2 scFv-phages have potential in the therapy of systemic infection caused by C. albicans.

Alt a 15 is a new cross-reactive minor allergen of Alternaria alternata.

Alternaria alternata is one of the most common saprophytes worldwide that is clinically and epidemiologically associated with severe asthma. Therefore, the identification and characterization of all A. alternata allergens are of major clinical importance. This study describes a new cross-reactive A. alternata allergen that was officially named Alt a 15 by the official Allergen Nomenclature Subcommittee. The complete coding region for Alt a 15 was amplified using 5' and 3' rapid amplification of cDNA ends and PCR. The recombinant protein was produced in Escherichia coli as a 65-kDa fusion protein, and the protein sequence exhibits high homology with several important fungal allergens. Immunoblotting analyses revealed that IgE antibodies from A. alternata-sensitized patients (n=59) bound to rAlt a 15 with a prevalence of 10.2%. All patients who presented sIgE to rAlt a 15 were apparently poly-sensitized to A. alternata and C. lunata. The extensive cross-reactivity between A. alternata and C. lunata serine proteases was confirmed using immunoblotting inhibition assays. Overall, Alt a 15 is an important new cross-reactive allergen of A. alternata that explains some allergies to A. alternata without Alt a 1 sensitization and initial diagnostic errors for allergies to Alternaria. This molecule may improve the accuracy of the diagnosis, the understanding, and the management of IgE-mediated fungal diseases.

Characterization of Anti-Citrinin Specific ScFvs Selected from Non-Immunized Mouse Splenocytes by Eukaryotic Ribosome Display.

Single chain variable fragments (scFvs) against citrinin (CIT) were selected from a scFv library constructed from the splenocytes of non-immunized mice by an improved eukaryotic ribosome display technology in this study. Bovine serum albumin (BSA)/ CIT-BSA and ovalbumin (OVA)/ CIT-OVA were used as the antigens to select specific anti-CIT scFvs. Eukaryotic in situ RT-PCR method was used to recover the selected mRNA after every affinity selection. After six rounds of ribosome display, expression vector pTIG-TRX carrying specific scFv DNAs were constructed and transformed into Escherichia coli BL21 (DE3) for protein expression. Thirteen positive clones were selected out of which three (designated 23, 68 and 109) showed high binding activity and specificity to CIT by indirect ELISA, while no clone showed binding activity with carrier proteins. The three scFvs showed high specificity to CIT and the cross reactivity with other mycotoxins was below 0.01% as determined by indirect competitive ELISA. These specific scFvs offer a potential novel immunoassay method for CIT residues. This study confirmed the effectiveness of the improved eukaryotic ribosome display system and could be used as a reference for the selection of scFvs specific to other small molecules using ribosome display.

Variable Region Identical IgA and IgE to Cryptococcus neoformans Capsular Polysaccharide Manifest Specificity Differences.

In recent years several groups have shown that isotype switching from IgM to IgG to IgA can affect the affinity and specificity of antibodies sharing identical variable (V) regions. However, whether the same applies to IgE is unknown. In this study we compared the fine specificity of V region-identical IgE and IgA to Cryptococcus neoformans capsular polysaccharide and found that these differed in specificity from each other. The IgE and IgA paratopes were probed by nuclear magnetic resonance spectroscopy with (15)N-labeled peptide mimetics of cryptococcal polysaccharide antigen (Ag). IgE was found to cleave the peptide at a much faster rate than V region-identical IgG subclasses and IgA, consistent with an altered paratope. Both IgE and IgA were opsonic for C. neoformans and protected against infection in mice. In summary, V-region expression in the context of the ϵ constant (C) region results in specificity changes that are greater than observed for comparable IgG subclasses. These results raise the possibility that expression of certain V regions in the context of α and ϵ C regions affects their function and contributes to the special properties of those isotypes.

Western blotting as a tool for the serodiagnosis of farmer's lung disease: validation with Lichtheimia corymbifera protein extracts.

Electrosyneresis and double diffusion are immunoprecipitation techniques commonly used in the serological diagnosis of Farmer's lung disease (FLD). These techniques are reliable but lack standardization. The aim of this study was to evaluate Western blotting for the serodiagnosis of FLD. We carried out Western blotting with an antigenic extract of Lichtheimia corymbifera, an important aetiological agent of the disease. The membranes were probed with sera from 21 patients with FLD and 21 healthy exposed controls to examine the IgG antibody responses against purified somatic antigens. Given the low prevalence of the disease, 21 patients could be considered as a relevant series. Four bands were significantly more frequently represented in membranes probed with FLD sera (bands at 27.7, 40.5, 44.0 and 50.5 kDa) than those probed with control sera. We assessed the diagnostic value of different criteria alone or in combination. The diagnostic accuracy of the test was highest with the inclusion of at least two of the following criteria: at least five bands on the strip and the presence of one band at 40.5 or 44.0 kDa. Sensitivity, specificity and positive and negative predictive values were all 81%, and the odds ratio was 18.06. Inclusion of bands of high intensity diminished rather than improved the diagnostic value of the test. We concluded that Western blotting is a valuable technique for the serodiagnosis of FLD. The industrial production of ready-to-use membranes would enable the routine use of this technique in laboratories, and provide reliable and standardized diagnostic results within a few hours.

Immunoproteomic analysis reveals a convergent humoral response signature in the Sporothrix schenckii complex.

Sporotrichosis is a polymorphic disease that affects both humans and animals worldwide. The fungus gains entry into a warm-blooded host through minor trauma to the skin, typically by contaminated vegetation or by scratches and bites from a diseased cat. Cellular and humoral responses triggered upon pathogen introduction play important roles in the development and severity of the disease. We investigated molecules expressed during the host-parasite interplay that elicit the humoral response in human sporotrichosis. For antigenic profiling, Sporothrix yeast cell extracts were separated by two-dimensional (2D) gel electrophoresis and probed with pooled sera from individuals with fixed cutaneous and lymphocutaneous sporotrichosis. Thirty-five IgG-seroreactive spots were identified as eight specific proteins by MALDI-ToF/MS. Remarkable cross-reactivity among Sporothrix brasiliensis, Sporothrix schenckii, and Sporothrix globosa was noted and antibodies strongly reacted with the 70-kDa protein (gp70), irrespective of clinical manifestation. Gp70 was successfully identified in multiple spots as 3-carboxymuconate cyclase. In addition, 2D-DIGE characterization suggested that the major antigen of sporotrichosis undergoes post-translational modifications involving glycosylation and amino acid substitution, resulting in at least six isoforms and glycoforms that were present in the pathogenic species but absent in the ancestral non-virulent Sporothrix mexicana. Although a primary environmental function related to the benzoate degradation pathway of aromatic polymers has been attributed to orthologs of this molecule, our findings support the hypothesis that gp70 is important for pathogenesis and invasion in human sporotrichosis. We propose a diverse panel of new putative candidate molecules for diagnostic tests and vaccine development. BIOLOGICAL SIGNIFICANCE: Outbreaks due to Sporothrix spp. have emerged over time, affecting thousands of patients worldwide. A sophisticated host-pathogen interplay drives the manifestation and severity of infection, involving immune responses elicited upon traumatic exposure of the skin barrier to the pathogen followed by immune evasion. Using an immunoproteomic approach we characterized proteins of potential significance in pathogenesis and invasion that trigger the humoral response during human sporotrichosis. We found gp70 to be a cross-immunogenic protein shared among pathogenic Sporothrix spp. but absent in the ancestral environmental S. mexicana, supporting the hypothesis that gp70 plays key roles in pathogenicity. For the first time, we demonstrate with 2D-DIGE that post-translational modifications putatively involve glycosylation and amino acid substitution, resulting in at least six isoforms and glycoforms, all of them IgG-reactive. These findings of a convergent humoral response highlight gp70 as an important target serological diagnosis and for vaccine development among phylogenetically related agents of sporotrichosis.

Radiolabeled Antibodies for Therapy of Infectious Diseases.

Novel approaches to the treatment of infectious diseases are urgently needed. This need has resulted in renewing the interest in antibodies for therapy of infectious diseases. Radioimmunotherapy (RIT) is a cancer treatment modality that utilizes radiolabeled monoclonal antibodies. During the last decade we have translated RIT into the field of experimental fungal, bacterial, and HIV infections. In addition, successful proof of principle experiments with radiolabeled pan-antibodies that bind to antigens shared by major pathogenic fungi have been performed in vitro. The armamentarium of pan-antibodies would result in reducing our dependence on microorganism-specific antibodies and thus would speed up the development of RIT for infections. We believe that the time is ripe for deploying RIT in the clinic to combat infectious diseases.

Design of a Candida albicans disaccharide conjugate vaccine by reverse engineering a protective monoclonal antibody.

A disaccharide-chicken serum albumin conjugate vaccine against Candida albicans infections has been developed by reverse engineering a protective monoclonal antibody, C3.1. The binding site of C3.1 binds short oligosaccharides of ß1,2-linked mannopyranose residues present in the fungal cell wall phosphomannan. By delineating the fine detail of the molecular recognition of the cell wall ß-mannan antigen, a disaccharide epitope was deduced to be the minimum size epitope that should induce the formation of protective antibody. Sequential functional group replacement of disaccharide hydroxyl groups to yield a series of monodeoxy and mono-O-methyl ß1,2-linked mannobioside congeners established that three hydroxyl groups are essential for binding. Two of these, O-3 and O-4, are located on the internal mannose residue of the disaccharide, and a third, O-3', is located on the terminal mannose. Synthesis of a series of trisaccharides that mandate binding of either the reducing or nonreducing disaccharide epitopes provided the final indication that a disaccharide protein conjugate should have the potential to induce protective antibody. When disaccharide was conjugated to chicken serum albumin this vaccine produced antibodies in rabbits that recognized the native cell wall phosphomannan. In proof of concept protection experiments, three immunized rabbits showed a reduction in fungal burden when challenged with live C. albicans.

Synthesis of three trisaccharide congeners to investigate frame shifting of ß1,2-mannan homo-oligomers in an antibody binding site.

Homopolysaccharides such as the protective ß1,2-mannan present in the cell wall of Candida albicans have the capability to bind to antibody in numerous frame shifted modes. A protective monoclonal antibody C3.1 binds this antigen and exhibits a unique binding profile where di and trisaccharides are the most potent inhibitors, while the intrinsic affinities of tetrasaccharide and larger oligomers dramatically decrease with increasing chain length. The design, synthesis and inhibitory activity of three ß1,2-linked trisaccharide congeners is reported. Selective functional group modification was introduced at the terminal reducing or non-reducing mannose residues so that each trisaccharide would be capable of binding to antibody in only one of the possible frame shifted modes. Inhibition data show that C3.1 has the highest affinity for internally situated disaccharide epitopes but can bind the terminal non-reducing disaccharide of a trisaccharide epitope.

[Using of antibodies against Microsporia Hsp70 family proteins for analysis of secretome of intracellular parasites].

Microsporidia is a large group of fungi-related unicellular parasites with obligate intracellular lifestyle. Unlike other protozoan intracellular parasites (Kinetoplastida and Apicomplexa), most microsporidian species develop in direct contact with the host cell cytoplasm. This fact, acquisition of unique transporters to exploit host metabolic system (alongside the strong minimization of own machinery) and predicted repertoire of microsporidia secretome altogether suggest an active role of parasite proteins in the control of infected cell. Lack of information about secretome of microsporidia intracellular stages is largely due to the methodological difficulties of working with the obligate intracellular parasites. An important problem of such study is the contamination of preparations of host cell cytoplasm by inner (nonsecreted) parasite proteins. Even the homogenization of infected tissue in mild conditions and removal of parasite cells by low-speed centrifugation may result in their partial disruption. We expressed the fragments of three Hsp70 family chaperones from the microsporidium Paranosema (Antonospora) locustae in bacteria Escherichia coli. Immunoblotting with proteins of microsporidia intracellular stages and infected host tissue (locust fat bodies) demonstrated that antibodies against recombinant polypeptides may be used to monitor the integrity of parasite cells during homogenization of infected host tissue and subsequent removal of parasites by centrifugation.

An altered camelid-like single domain anti-idiotypic antibody fragment of HM-1 killer toxin: acts as an effective antifungal agent.

Phage-display and competitive panning elution leads to the identification of minimum-sized antigen binders together with conventional antibodies from a mouse cDNA library constructed from HM-1 killer toxin neutralizing monoclonal antibody (nmAb-KT). Antigen-specific altered camelid-like single-domain heavy chain antibody (scFv K2) and a conventional antibody (scFv K1) have been isolated against the idiotypic antigen nmAb-KT. The objectives of the study were to examine (1) their properties as compared to conventional antibodies and also (2) their antifungal activity against different pathogenic and non-pathogenic fungal species. The alternative small antigen-binder, i.e., the single-domain heavy chain antibody, was originated from a conventional mouse scFv phage library through somatic hyper-mutation while selection against antigen. This single-domain antibody fragment was well expressed in bacteria and specifically bound with the idiotypic antigen nmAb-KT and had a high stability and solubility. Experimental data showed that the binding affinity for this single-domain antibody was 272-fold higher (K(d)=1.07×10(-10) M) and antifungal activity was three- to fivefold more efficient (IC(50)=0.46×10(-6) to 1.17×10(-6) M) than that for the conventional antibody (K(d)=2.91×10(-8) M and IC(50)=2.14×10(-6) to 3.78×10(-6) M). The derived single-domain antibody might be an ideal scaffold for anti-idiotypic antibody therapy and the development of smaller peptides or peptide mimetic drugs due to their less complex antigen-binding site. We expect that such single-domain synthetic antibodies will find their way into a number of biotechnological or medical applications.

Analysis of the cellular Aspergillus fumigatus proteome that reacts with sera from rabbits developing an acquired immunity after experimental aspergillosis.

Invasive aspergillosis caused by the mould Aspergillus fumigatus is a life-threatening lung or systemic infection in the immunocompromised host. In this study, a protective immune response against the disease was achieved in two infected rabbits, and the cellular fungal antigenic proteome that mediated such a response was investigated against the background of vaccine development efforts. Altogether, 59 different Aspergillus proteins were found becoming reactive in the course of the developing immunity, many of which are described in this context for the first time. These included proteins related to oxidative stress management, glycolysis and other metabolic pathways. As oxidative stress is suspected to be one of the major defense mechanisms, the results may indicate at least in part a continuous response of the pathogen to evade the host's immune system. In addition, proteins with suspected cell surface association or crucial function for fungal cell development were identified. As these antigens are newly recognized during the process of the developing immunoprotection, they may not only represent valuable infection markers but also importantly broaden the list of possible vaccine candidates.

Effect of anti-glycosphingolipid monoclonal antibodies in pathogenic fungal growth and differentiation. Characterization of monoclonal antibody MEST-3 directed to Manpalpha1-->3Manpalpha1-->2IPC.

BACKGROUND: Studies carried out during the 1990's demonstrated the presence of fungal glycoinositol phosphorylceramides (GIPCs) with unique structures, some of them showed reactivity with sera of patients with histoplasmosis, paracoccidioidomycosis or aspergillosis. It was also observed that fungal GIPCs were able to inhibit T lymphocyte proliferation "in vitro", and studies regarding the importance of these molecules to fungal survival showed that many species of fungi are vulnerable to inhibitors of sphingolipid biosynthesis. RESULTS: In this paper, we describe a detailed characterization of an IgG2a monoclonal antibody (mAb), termed MEST-3, directed to the Paracoccidioides brasiliensis glycolipid antigen Pb-2 (Manpalpha1-->3Manpalpha1-->2IPC). mAb MEST-3 also recognizes GIPCs bearing the same structure in other fungi. Studies performed on fungal cultures clearly showed the strong inhibitory activity of MEST-3 on differentiation and colony formation of Paracoccidioides brasiliensis, Histoplasma capsulatum and Sporothrix schenckii. Similar inhibitory results were observed when these fungi where incubated with a different mAb, which recognizes GIPCs bearing terminal residues of beta-D-galactofuranose linked to mannose (mAb MEST-1). On the other hand, mAb MEST-2 specifically directed to fungal glucosylceramide (GlcCer) was able to promote only a weak inhibition on fungal differentiation and colony formation. CONCLUSIONS: These results strongly suggest that mAbs directed to specific glycosphingolipids are able to interfere on fungal growth and differentiation. Thus, studies on surface distribution of GIPCs in yeast and mycelium forms of fungi may yield valuable information regarding the relevance of glycosphingolipids in processes of fungal growth, morphological transition and infectivity.