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Major membrane proteins and lipoproteins as highly variable immunogenic surface components and strain-specific
M Droesse1, G Tangen, I Gummelt
1Institut für Mikrobiologie und Tierseuchen, Tierärztliche Hochschule Hannover, Germany.
Abstract:
Surface antigenic variation was investigated in Mycoplasma arthritidis, an agent that produces chronic arthritis in rats which shares several features with many mycoplasma-induced diseases and thus defines a well-characterized model system. Hyperimmune rabbit antisera (anti-ISR1, anti-PG6, anti-H606 and anti-158p10) to whole M. arthritidis organisms were used as immunological probes in Western immunoblots of four M. arthritidis prototype strains (ISR1, PG6, H606 and D263) and five rat-passaged substrains (ISR1p1, ISR1p7, ISR1p8, 158p10 and D263p1). Several prominent antigens were identified that varied in expression. By Triton X-114 phase fractionation and treatment of whole cells with trypsin and carboxypeptidase Y, these strain-variant antigens were shown to be integral membrane proteins with C-termini and portions of the polypeptide chains oriented outside the membrane. Western blot immunoscreening of a large number of randomly selected clonal isolates and well-established clonal lineages from stock cultures of M. arthritidis ISR1p7, 158p10, PG6 and H606 revealed an expanded repertoire of variant membrane proteins whose expression was subject to independent, reversible phase variation. Colony immunoblots of these clonal populations with a hyperimmune rabbit antiserum to a gel-purified variant membrane protein (P36) showed that this phase switching occurred at a high frequency (10(-4) to 10(-2) per generation). Detailed immunological and biochemical characterization of the phase-variant membrane proteins demonstrated that they are: (i) antigenically related or distinct; (ii) apparently specific to particular strain populations; (iii) proteins or lipoproteins; (iv) major immunogens of M. arthritidis, recognized by serum antibodies from convalescent rat; and (v) able to undergo variation in expression during in vivo passage. Thus, M. arthritidis possesses a complex system capable of creating large repertoires of cell surface phenotypes which may affect the multiple interactions of this organism with its host and dictate its potential as a successful infectious agent and pathogen.
Insights
Mycoplasma arthritidis exhibits surface antigenic variation through a complex system of phase-variable membrane proteins. This variation allows the bacterium to generate diverse cell surface phenotypes, potentially impacting host interactions and pathogenicity.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Mycoplasma arthritidis is a well-characterized model for studying mycoplasma-induced diseases, particularly chronic arthritis in rats.
- Surface antigenic variation is a key mechanism employed by many pathogens to evade host immune responses.
Purpose of the Study:
- To investigate surface antigenic variation in Mycoplasma arthritidis.
- To identify and characterize the variant antigens and the mechanisms regulating their expression.
Main Methods:
- Western immunoblots using hyperimmune antisera against M. arthritidis strains.
- Triton X-114 phase fractionation and enzymatic treatments (trypsin, carboxypeptidase Y) to characterize membrane proteins.
- Western blot and colony immunoblots of clonal isolates and lineages to assess phase variation frequency.
Main Results:
- Identified prominent, strain-variant integral membrane proteins with extracellularly oriented portions.
- Revealed an expanded repertoire of variant membrane proteins exhibiting independent, reversible phase variation at high frequency (10^-4 to 10^-2 per generation).
- Characterized these phase-variant proteins as antigenically related or distinct, potentially strain-specific, major immunogens recognized by convalescent rat sera, and capable of in vivo expression variation.
Conclusions:
- Mycoplasma arthritidis possesses a sophisticated system for generating diverse cell surface phenotypes through phase-variable membrane proteins.
- This antigenic variation system likely contributes to the organism's ability to interact with and persist in the host.
- The findings enhance understanding of M. arthritidis pathogenesis and host-pathogen dynamics.