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Antibody-independent complement consumption by Micropolyspora faeni
Abstract:
Micropolyspora faeni is an etiologic agent of hypersensitivity pneumonitis, a disease with an ill-defined mechanism of pathogenesis. Many reports have suggested an immunologic mechanism. A number of laboratories have demonstrated a nonantibody-mediated activation of the complement cascade. This study was undertaken to define the pathway of the complement consumption induced by M. faeni. We utilized an extract of M. faeni grown on synthetic media rather than the more common double dialysis extracts. Complement consumption by this extract was easily demonstrable in the absence of detectable antibody, but was inhibited by EDTA and MgEGTA. With the exception f C1, all of the early components of the classical pathway were markedly reduced following incubation of normal human serum with this extract. C1 was poorly consumed. In addition, factor B conversion to B was not inhibited by 10 mM MgEGTA suggests that the alternative pathway may also be affected. The generation of M. faeni-dependent chemotactic factor(s) from serum demonstrates that the complement cascade is being activated rather than inhibited.
Insights
Micropolyspora faeni activates the complement cascade, a key part of the immune response, in hypersensitivity pneumonitis. This study clarifies the specific complement pathways involved in this M. faeni-induced reaction.
Area of Science:
- Immunology
- Microbiology
Background:
- Micropolyspora faeni is linked to hypersensitivity pneumonitis.
- The pathogenesis of this disease is not fully understood, but immune mechanisms are suspected.
- Previous studies indicate non-antibody-mediated complement activation by M. faeni.
Purpose of the Study:
- To elucidate the specific complement pathway(s) activated by Micropolyspora faeni.
- To investigate the role of M. faeni extracts in complement consumption.
- To understand the immunologic basis of hypersensitivity pneumonitis.
Main Methods:
- Utilized a synthetic media extract of M. faeni.
- Assessed complement consumption in normal human serum incubated with M. faeni extract.
- Employed EDTA and MgEGTA to inhibit complement pathways.
- Analyzed consumption of classical and alternative pathway components.
- Measured generation of M. faeni-dependent chemotactic factors.
Main Results:
- M. faeni extract induced complement consumption without detectable antibody.
- Complement consumption was inhibited by EDTA and MgEGTA.
- Early classical pathway components (except C1) were significantly reduced.
- Factor B conversion was not inhibited by MgEGTA, suggesting alternative pathway involvement.
- M. faeni activated complement, leading to chemotactic factor generation.
Conclusions:
- Micropolyspora faeni activates both classical and alternative complement pathways.
- This activation is antibody-independent and contributes to hypersensitivity pneumonitis pathogenesis.
- The findings provide insights into the immunologic mechanisms of M. faeni-induced lung disease.