Studies on Alternaria allergens. I. Isolation of allergens from Alternaria tenuis and Alternaria solani

Cross-reactivity of Aspergillus, Penicillium, and Stachybotrys antigens using affinity-purified antibodies and immunoassay

In this study, the author examined the cross-reactivities of Stachybotrys chartarum, Aspergillus niger/fumigatus, and Penicillium notatum with affinity-purified rabbit sera. The molds were grown for expression of maximum numbers of antigens, after which they were extracted and mixed with commercially available extracts. The mixture was used for antibody preparation in rabbits, measurement of antibody levels, and for the demonstration of the degree of cross-reactivity. Control rabbits were injected with saline, yet they produced significant levels of immunoglobulin G antibodies against all mold extracts tested. The author interpreted this result to mean that sera obtained from rabbits immunized with pure mold extracts likely reflected cross-reactivity with other molds. Therefore, only affinity-purified antibodies and the most sensitive immunoassay technique (i.e., enzyme-linked immunosorbent assay [ELISA]) were used for the cross-inhibition studies. The antigenic cross-reactivities were as follows: (a) between Aspergillus and Penicillium, 19.6-21.0%; (b) between Stachybotrys and Aspergillus, 8.2-8.7%; and (c) between Stachybotrys and Penicillium, 7.0-9.6%. The findings of this study demonstrate that cross-reactivity studies between different molds require the use of affinity-purified antibodies and a sensitive and quantitative assay with untreated antigens. With the use of such an assay, it was determined that the cross-reactivity between Stachybotrys, Aspergillus, and Penicillium was at approximately 10%, which is less widespread than previously believed.

Examination of Alternaria alternata mutagenicity and effects of nitrosylation using the Ames Salmonella test

Molds of the genus Alternaria are common food pathogens responsible for the spoilage of fruits, vegetables, grains, and nuts. Although consumption of Alternaria alternata-contaminated foodstuffs has been implicated in an elevated incidence of esophageal carcinogenesis, the mutagenic potencies of several A. alternata toxins seem unable to account for the levels of activity found using crude mycelial extracts. In this study, the mutagenic effects of nitrosylation were examined with the major Alternaria metabolites Altenuene (ALT), Alternariol (AOH), Alternariol Monomethyl Ether (AME), Altertoxin I (ATX I), Tentoxin (TENT), Tenuazonic Acid (TA), and Radicinin (RAD) using the Ames Salmonella strains TA98 and TA100. In the absence of nitrosylation, ATX I was mutagenic when tested from 1 to 100 microg/plate in TA98 with rat liver S9 for activation, while AOH and ATX I were weakly mutagenic +/- S9 in TA100. Incubation with nitrite generally increased mutagenic potencies with ATX I strongly mutagenic +/- S9 in both TA98 and TA100, while ALT, AOH, AME, and RAD responses were enhanced in TA100 + S9. However, subsequent examination of three extracts made from A. alternata culture broth, acetone-washed mycelia, and the acetone washes showed a different mutagenic response with both broth and acetone washes directly mutagenic in TA98 and TA100 but with a reduced response + S9. The acetone-washed mycelial extract was found to have the lowest mutagenic activity of the three extracts tested. Nitrosylation had little effect on the mutagenicity of any of the extracts. Thus, while nitrosylation increases the mutagenicity of ATX I, and to a lesser extent that of several other Alternaria toxins, the results demonstrate that Alternaria produces a major mutagenic activity with a S. typhimurium response different from that found with the purified toxins. Efforts are currently underway to chemically identify this mutagenic species. Published 2001 Wiley-Liss, Inc.

Isolation and immunobiochemical characterization of a major allergen (65 kDa) from Fusarium equiseti

Fusarium equiseti is one of the most important species in the class Deuteromycetes (Fungi Imperfecti). For proper diagnosis and immunotherapy, isolation and characterization of allergens of F. equiseti are necessary. In the present study, culture filtrate (CF) extract of F. equiseti was resolved into 35-37 bands on isoelectric focusing pI (3-9) and SDS-PAGE (mol. wt. 10-100 kDa). Most of them were glycoproteins, as identified by PAS staining. F. equiseti CF revealed 15 allergenic proteins on immunoblot with an allergic serum pool. It was fractionated into nine fractions (I-IX) on a Superose-12 column by FPLC. Fraction IV (65 kDa) and fraction VI (25 kDa) were found to be highly allergenic by IgE ELISA. A 65-kDa protein was observed as a major allergen because it was recognized by most of the patient sera on immunoblot. After elution from SDS-PAGE gel, it gave two bands of pI 7.4 and 6.0. Inhibition in IgE-binding components of F. equiseti CF with CF extracts of F. solani and F. moniliforme by immunoprint inhibition assay indicated the allergenicity shared between the extracts of Fusarium species. Data suggested that the 65-kDa is the major allergen in the Fusarium species and can be used for the treatment of allergic patients.

Production of a recombinant protein from Alternaria containing the reported N-terminal of the Alt a1 allergen

Allergen content of extract derived from Alternaria is somewhat variable. Allergenic molecules from Alternaria that appear as differing molecular size bands on IgE probed immunoblots may have a great deal of sequence homology and differ only in the length of the amino acid chain. One method to study this problem is to produce recombinant proteins from Alternaria. To explore these possibilities, the following experiments were performed. A strain of Alternaria was grown on minimum salts and glucose in a fermentation container with constant stirring and aeration. Rapidly expanding mycelia were removed from the culture and mRNA was extracted. Purified mRNA was reacted with reverse transcriptase and an aliquot of first copy single strand DNA was enriched for the presence of DNA coding for an Alternaria allergen by PCR amplification. Modified DNA was then spliced into lambda gt11 phage and yielded a recombinant library with 10(5) PFU. The library was screened for the presence of allergenic proteins using IgE containing human sera from Alternaria-sensitive patients. Positive plaques were cloned. PCR analysis of positive clones using an oligonucleotide from the reported N-terminal sequence of Alt a1 indicated an insert of 295 base pairs. Sequence analysis yielded a reading frame containing 84 amino acid and confirmed that this segment contained the code for the reported N-terminal amino acid sequence of Alt a1. A computer search for this sequence found no homologous proteins in the Entrez sequences. Northern blotting studies on RNA purified from nine strains of Alternaria with the radiolabeled 247 BP DNA fragment indicated that this sequence was present in all strains. The 247 BP nucleotide was spliced into the Pflag vector and clones containing insert in the proper reading frame were identified. The presence of recombinant protein in the clones was verified by SDSPAGE time studies. Protein produced in time studies was shown by immunoblotting and sandwich EIA to bind human IgE from Alternaria sensitive patients. This recombinant protein, containing amino acid sequence for Alt a1, is bound by human IgE and therefore should be useful as a model for studying allergy to the native Alternaria glycoprotein. Further research should define where this sequence occurs in the Alternaria genome and should determine the sequence of the entire protein.

Studies on shared antigenic/allergenic components among fungi

Fungal allergens have been found to be one of the most prevalent aeroallergens in India. Knowledge of shared/unique components among different fungi is necessary for proper diagnosis and treatment of patients allergic to fungi. In the present study, crude extracts (CE) of 11 common fungi (Alternaria alternata, Aspergillus flavus, Asp. fumigatus, Asp. niger, Asp. tamarii, Asp. versicolor, Cladosporium herbarum, Curvularia lunata, Mucor hiemalis, Penicillium citrinum, and Fusarium solani) were characterized by isoelectric focusing (IEF), SDS-PAGE, and immunoblot. On IEF (pI 3-9), the number of protein bands was found to be greatest (46) in M. hiemalis extract. SDS-PAGE exhibited a varied number of bands, generally 18-40, with mol. mass ranging from 14 to 100 kDa. IgG-specific immunoprint using rabbit anti-F. solani CF antibodies demonstrated a mol. mass distribution of shared antigenic proteins of 14-100 kDa in most of the fungi. Shared allergenicity was observed in a number of allergenic proteins in fungal extracts with mol. mass ranging between 14 and 70 kDa on IgE-specific immunoblot using pooled sera of patients allergic to Fusarium. A 45-kDa protein was found to be common among these fungi on immunoblot with patients as well as with rabbit antibodies. F. solani CF extract contained more antigenic/allergenic proteins than F. solani CE. It was concluded that F. solani CF shared several antigenic/allergenic components with CE of other common fungi. This fact needs to be taken into account when fungal extracts are used in diagnosis and immunotherapy of allergic patients.

Comparison of different extraction methods of Alternaria allergens

Spore and mycelial allergens of two species of Alternaria (A. brassicicola and A. alternata) extracted under two different conditions were analyzed by radiorocket immunoelectrophoresis, crossed radioimmunoelectrophoresis, and Western blotting with a pool of sera from Alternaria-allergic patients. More allergens were extracted after disruption of the cells if protease inhibitors and a phenol-binding component were included in the homogenization buffer. However, the 31 kDa major allergen was extracted in about the same amount, either by incubation or by cell breakage of the cells. This 31 kDa allergen was present in higher concentration in the mycelium than in the spore. The difference between the two species studied is less than between spore and mycelium from the same species.

Standardization of fungal allergens

The ability of various fungi to induce human IgE-mediated disease, especially allergic asthma, has been well established. The relative clinical importance of fungal aeroallergens varies considerably in different geographic areas. The magnitude of exposure to fungal aeroallergens can be quantitated more precisely by newer immunochemical assays than by more traditional fungal cultures or quantitation of fungal spores by microscopy. Although the wide variations in biologic potency among commercial mold allergenic extracts have been appreciated for decades, only recently have laboratory technologic advances and the production of international reference extracts permitted the development of standardized fungal extracts of defined potency. Future efforts should be directed toward documenting the expected diagnostic and therapeutic advantages of such standardized fungal extracts.

Immunological studies on Alternaria sensitivity. Use of crossed radioimmunoelectrophoresis, precipitins and enzyme-linked immunosorbent assay

Characterization of the immunological response to Alternaria in sensitive subjects is not complete. We used crossed radioimmunoelectrophoresis (CRIE) to identify antigens in Alternaria extracts reacting with IgE antibody in five patients with Alternaria-sensitive asthma, four with Alternaria-induced rhinitis, three non-allergic asthmatics, and three normal controls. All five Alternaria-asthma patients and three of four Alternaria-rhinitis patients showed IgE binding to a third antigen. These results suggest an analogy of Alternaria antigens with that found in ragweed pollen extracts, i.e. that IgE antibody is directed against more than one antigen. Using the enzyme-linked immunosorbent assay (ELISA), we found a significant difference (P less than 0.05, unpaired Student's t-test) in IgG binding between Alternaria-sensitive asthmatics and normal controls. There was no apparent difference in IgG binding between untreated Alternaria-sensitive asthmatics and those receiving high-dose immunotherapy.