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Infect. Immun., 05 1997, 1773-1785, Vol 65, No. 5
C Citti, MF Kim and KS Wise
Variation in Vlp surface proteins of Mycoplasma hyorhinis was evaluated in
terms of its role in determining susceptibility of organisms to growth
inhibition by host antibodies (Abs). High-frequency switching of Vlp
surface lipoproteins has been studied in isogenic lineages of M. hyorhinis
SK76. In these lineages, the products of three genes, vlpA, vlpB, and vlpC,
are subject to phase and size variation in vitro, which occur through
distinct mutator elements that independently govern the expression of each
vlp gene (promoter mutations) or the size of the vlp gene product (by
intragenic expansion or contraction of a 3' region containing tandem
repeats). Isogenic clonal variants of M. hyorhinis SK76 expressing distinct
profiles of Vlp products were assessed for their susceptibility to
complement-independent growth inhibition by serum Abs of swine
experimentally infected with the arthritigenic SK76 strain. Invariably,
variants expressing longer versions of VlpA, VlpB, or VlpC (each expressed
individually) were completely resistant to host immune serum Abs, whereas
variants expressing shorter allelic versions of each Vlp were susceptible.
The target of growth-inhibiting Abs was not the Vlp products, since removal
of anti-Vlp Abs had no effect on the inhibitory activity of the host immune
serum on susceptible variants. Escape variant populations derived by
propagating susceptible variants in an immune (versus control) host serum
revealed a strong selection for the long-Vlp phenotype, irrespective of the
identity of the Vlp expressed. Apparent mutational pathways of acquiring
the protective phenotype included mutational switches to express long vlp
genes that had been transcriptionally silent or switches to elongate
expressed vlp genes. These results suggest that a major function of the Vlp
system is to shield the wall-less mycoplasma surface from host Abs capable
of binding vital (and as-yet-unidentified) surface antigens of this
organism.
Copyright © 1997, American Society for Microbiology
Elongated versions of Vlp surface lipoproteins protect Mycoplasma hyorhinis escape variants from growth-inhibiting host antibodies
Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri-Columbia, 65212, USA.
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