Identification of Microcystis aeruginosa Peptides Responsible for Allergic Sensitization and Characterization of Functional Interactions between Cyanobacterial Toxins and Immunogenic Peptides

BACKGROUND The cyanobacterium species Microcystis aeruginosa produces microcystin and an array of diverse metabolites believed responsible for their toxicity and/or immunogenicity. Previously, chronic rhinitis patients were demonstrated to elicit a specific IgE response to nontoxic strains of M. aeruginosa by skin-prick testing, indicating that cyanobacteria allergenicity resides in a non-toxin-producing component of the organism. OBJECTIVES We sought to identify and characterize M. aeruginosa peptide(s) responsible for allergic sensitization in susceptible individuals, and we investigated the functional interactions between cyanobacterial toxins and their coexpressed immunogenic peptides. METHODS Sera from patients and extracts from M. aeruginosa toxic [MC(+)] and nontoxic [MC(-)] strains were used to test IgE-specific reactivity by direct and indirect ELISAs; 2D gel electrophoresis, followed by immunoblots and mass spectrometry (MS), was performed to identify the relevant sensitizing peptides. Cytotoxicity and mediator release assays were performed using the MC(+) and MC(-) lysates. RESULTS We found specific IgE to be increased more in response to the MC(-) strain than the MC(+) strain. This response was inhibited by preincubation of MC(-) lysate with increasing concentrations of microcystin. MS revealed that phycocyanin and the core-membrane linker peptide are the responsible allergens, and MC(-) extracts containing these proteins induced β-hexosaminidase release in rat basophil leukemia cells. CONCLUSIONS Phycobiliprotein complexes in M. aeruginosa have been identified as the relevant sensitizing proteins. Our finding that allergenicity is inhibited in a dose-dependent manner by microcystin toxin suggests that further investigation is warranted to understand the interplay between immunogenicity and toxicity of cyanobacteria under diverse environmental conditions. CITATION Geh EN, Ghosh D, McKell M, de la Cruz AA, Stelma G, Bernstein JA. 2015. Identification of Microcystis aeruginosa peptides responsible for allergic sensitization and characterization of functional interactions between cyanobacterial toxins and immunogenic peptides. Environ Health Perspect 123:1159-1166; http://dx.doi.org/10.1289/ehp.1409065.