Murine monoclonal antibodies binding to the specific antigens of Aspergillus fumigatus associated with allergic bronchopulmonary aspergillosis

Aspergillus-specific antibodies - Targets and applications

Aspergillus is a fungal genus comprising several hundred species, many of which can damage the health of plants, animals and humans by direct infection and/or due to the production of toxic secondary metabolites known as mycotoxins. Aspergillus-specific antibodies have been generated against polypeptides, polysaccharides and secondary metabolites found in the cell wall or secretions, and these can be used to detect and monitor infections or to quantify mycotoxin contamination in food and feed. However, most Aspergillus-specific antibodies are generated against heterogeneous antigen preparations and the specific target remains unknown. Target identification is important because this can help to characterize fungal morphology, confirm host penetration by opportunistic pathogens, detect specific disease-related biomarkers, identify new candidate targets for antifungal drug design, and qualify antibodies for diagnostic and therapeutic applications. In this review, we discuss how antibodies are raised against heterogeneous Aspergillus antigen preparations and how they can be characterized, focusing on strategies to identify their specific antigens and epitopes. We also discuss the therapeutic, diagnostic and biotechnological applications of Aspergillus-specific antibodies.

Generation of a monoclonal antibody that blocks epithelial binding of unopsonized particles

Alveolar macrophages (AMs) and epithelial cells (ECs) are the first cells in the lung to encounter inhaled environmental particles. The initial interaction between AMs and particles is mediated by specific scavenger receptors, but the nature of the structure(s) on ECs that also bind particles has not been well-described. To characterize the nature of the EC particle receptor, we screened a panel of mouse anti-human EC hybridomas for functional blockade of EC particle binding. This strategy identified a monoclonal antibody (MAb) (EPR1) that blocks binding of titanium dioxide (TiO(2)) particles to the EC line which served as the immunogen (A549), as well as to other EC lines (Beas 2-B, HTB54, HeLa, and MDA-MB-435S). EPR1 demonstrated specific labeling of ECs using immunohistology techniques and its expression could be quantitated by flow cytometry of permeabilized ECs in suspension. MAbs such as EPR1 may prove useful in further analysis of receptors for inhaled particles on lung epithelial cells.

Monoclonal antibodies against a 97-kilodalton antigen from Aspergillus flavus

We prepared a panel of five monoclonal antibodies (MAbs) directed against Aspergillus flavus that all reacted against one 97-kDa antigen by western blot (immunoblot). Flow cytometry demonstrated that these antibodies bound (in increasing degrees) to all morphologic stages of A. flavus growth: conidia, swollen conidia, and hyphae. Cross-reactivity among species was examined by enzyme-linked immunosorbent assay of fungal culture filtrates. Four MAbs reacted with 10 of 11 A. flavus isolates, and the fifth one reacted with 9 of them. One MAb also reacted with A. fumigatus, two reacted with A. niger, A. wentii, and A. nidulans, and all five reacted with A. ochraceus. None reacted with A. terreus, A. glaucus, A. versicolor, or a Penicillium species. Each MAb bound to A. flavus hyphae in formalin-fixed paraffin sections of a muscle biopsy from a confirmed human case of invasive aspergillosis. In summary, these MAbs identified a 97-kDa antigen found on A. flavus that is both surface bound and an exoantigen. Either the same or a cross-reacting antigen is present in A. fumigatus and other Aspergillus species.

Immunogenic potential of Aspergillus nidulans subcellular fractions and their polypeptide components

Cell-free extracts of the ascomycetous fungus Aspergillus nidulans were separated into three subcellular fractions: cell walls, total membranes and cytosol, and two different immunization protocols were used to raise antibodies against them in 12 New Zealand rabbits. The immune response was followed over time by dot and Western blot analyses to determine the immunogenic potential of each individual fraction and their polypeptide components. The IgG fractions, purified from pools of the best sera, were used to analyze in detail the antigenic composition of A. nidulans mycelium. The fast immunization protocol provided a much earlier response and higher sera titres. Cytosols and membranes were more immunogenic than cell walls and, in most cases, a positive correlation was shown between the titre of each serum and the number of detected antigens. The polypeptides of A. nidulans included six major immunodominant antigens of the molecular weights ranging between 13 and 200 kDa.

Aspergillus antigen-induced eosinophil differentiation in a murine model

Eosinophilia is a prominent feature of the cellular response in allergic and parasitic diseases. Allergic bronchopulmonary aspergillosis due to colonization of the lungs of some asthmatics with Aspergillus fumigatus is characterized by high levels of serum immunoglobulin E and peripheral blood (PB) and lung eosinophilia. This study investigates the role of eosinophils in the pathogenesis of allergic bronchopulmonary aspergillosis by using a mouse model. BALB/c mice were immunized intranasally and intraperitoneally with A. fumigatus antigens (Ag), and the eosinophils in PB and bone marrow (BM) were enumerated. Eosinophilopoiesis in BM cultures was studied in the presence of murine recombinant interleukin-5 (mrIL-5) and supernatants from pokeweed mitogen-stimulated spleen cells as the source of eosinophil differentiation factors. Eosinophils were quantitated by direct counting and by estimating eosinophil peroxidase activity. The results indicate that the percentage of eosinophils in the PB (5.77 +/- 1.17) and the BM (11.19 +/- 4.31) of mice exposed to A. fumigatus Ag was higher than in controls (PB, 2.42 +/- 0.76; BM, 5.12 +/- 2.79; P less than 0.01 for both). Similarly, a significant increase in eosinophils was observed in the BM population from mice exposed to A. fumigatus Ag compared with that in controls when cultured with murine recombinant interleukin-5 (23.13 +/- 7.14 versus 13.77 +/- 5.79, P less than 0.01), indicating that the mice exposed to A. fumigatus Ag had significantly greater numbers of eosinophil precursors in their BM. This study demonstrates that A. fumigatus Ag may be involved in the in vivo commitment of stem cells in the eosinophil differentiation pathway.

Monoclonal antibodies bind identically to both spores and hyphae of Aspergillus fumigatus

Immunoelectron microscopy (IEM) was used to determine the binding of six monoclonal antibodies (MoAbs) produced against Aspergillus fumigatus antigens present on or within the conidia and hyphae of the fungus. Antigen-antibody complexes were demonstrated in EM using labelled colloidal gold particles (15 nm). Three out of 6 MoAbs (C9, F12 and H10) reacted only with the cytoplasmic components of A. fumigatus while the remaining three (B12, F6G5 and D6E6) showed reactivity to both cytoplasm and cell wall of the conidia and hyphae. The results indicate that IEM is of considerable value in determining and selecting monoclonal antibodies having specific reactivity with diverse antigenic components.

Immunodiagnosis of aspergillosis

Aspergillus species are ubiquitous fungi and have been implicated as the causative agents of a variety of lung disorders in humans. These disorders include allergic, saprophytic, and systemic manifestations. The allergic disorders mainly affect atopic persons, and invasive or systemic diseases affect immunosuppressed individuals. Immunodiagnosis can help the practitioner diagnose these diseases. Demonstration of circulating antibodies is a useful criterion, but the lack of dependable and standardized antigens is a limiting factor in the diagnosis of most Aspergillus-induced diseases. Despite this limitation, however, immunodiffusion and enzyme-linked immunosorbent assays have been widely used for the detection of antibodies in the sera of patients with aspergillosis. Similarly, crude and semipurified antigens are being used to demonstrate skin hypersensitivity in patients, and several methods have been useful in the detection of antigenemia in patients with invasive aspergillosis. With a growing number of reports on the incidence of aspergillosis and an increase in the number of immunosuppressed individuals in the population, more rapid methods and more reliable reagents for immunodiagnosis are needed. With recent attempts at obtaining reliable reagents for through hybridoma technology and molecular biological techniques, substantial progress toward efficient immunodiagnosis may be achieved.

Characterization of a monoclonal antibody against concanavalin A binding antigen of Aspergillus fumigatus

A monoclonal antibody was produced against a Concanavalin A (Con A) binding major epitope of Aspergillus fumigatus using a novel method of immunization. The antigen was purified using monoclonal antibody affinity chromatography reacted with specific antibodies present in human sera. Both allergic bronchopulmonary aspergillosis and aspergilloma showed high levels of antibody, against this purified antigen, when compared to normal controls. Similar results were obtained when the monoclonal antibody was used in a capture antigen assay. The antibody reacted with several A. fumigatus extracts in rocket electrophoresis demonstrating a single precipitin arc, which disappeared when Con A intermediate gel was used. This monoclonal antibody demonstrated reactivity only with cytoplasmic components of hyphae and spores of A. fumigatus, when a colloidal gold was used as a probe in immunoelectron microscopy.