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Activation of the complement sequence by extracts of bacteria and fungi associated with hypersensitivity pneumonitis

J J Marx, D K Flaherty

    The Journal of Allergy and Clinical Immunology
    |April 1, 1976
    PubMed

    Insights

    Certain microbes, like Micropolyspora faeni, can trigger complement (C) consumption in hypersensitivity pneumonitis. This immune system response occurs even without detectable antibodies, suggesting direct microbial involvement in the disease process.

    Area of Science:

    • Immunology
    • Microbiology
    • Pulmonary Medicine

    Background:

    • Hypersensitivity pneumonitis (HP) is an immune-mediated lung disease.
    • Complement (C) system activation is implicated in HP pathogenesis.
    • The role of specific microbial antigens in complement consumption in HP requires further elucidation.

    Purpose of the Study:

    • To investigate complement consumption by antigens associated with hypersensitivity pneumonitis.
    • To determine if microbial extracts can activate the complement system independently of antibodies.

    Main Methods:

    • Complement consumption assays were performed using Micropolyspora faeni antigens.
    • The conversion of C3PA (C3 proactivator) to C3A was measured.
    • Extracts from various fungal and bacterial species were tested for complement-activating properties.

    Main Results:

    • Micropolyspora faeni, in the presence of precipitating antibodies, consumed complement similarly to a known antigen-antibody system (BSA-anti BSA).
    • An extract of M. faeni consumed complement and converted C3PA to C3A even without detectable antibodies.
    • Three Aspergillus species and two Thermoactinomyces vulgaris strains also demonstrated C3PA conversion activity.
    • Mucor racemosus, Hormodendrum sp., and Penicillium extracts did not convert C3PA.

    Conclusions:

    • Microbial antigens from Micropolyspora faeni can directly activate the complement system, leading to C3PA conversion.
    • This direct complement activation by microbial components may play a significant role in hypersensitivity pneumonitis pathogenesis.
    • Several other microbial species, including Aspergillus and Thermoactinomyces, possess similar complement-activating capabilities.

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