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Infection and Immunity, January 2000, p. 107-112, Vol. 68, No. 1
Institute for Laboratory Medicine, Lund
University, Lund, Sweden
Received 26 July 1999/Returned for modification 30 August
1999/Accepted 29 September 1999
Group A streptococcal M proteins are type-specific virulence
factors that inhibit phagocytosis. We used two M proteins, M5 and
Emm22, to analyze the influence of genetic background on the properties
of M proteins. Mutant strains, engineered to lack these M proteins,
were complemented with genes encoding the homologous or heterologous M
protein, and the complemented strains were analyzed for phagocytosis
resistance. Neither the M5 nor the Emm22 protein conferred phagocytosis
resistance in the heterologous background, but they did do so in the
homologous background. This was not due to lack of surface expression
in the heterologous background. Moreover, the M5 and Emm22
proteins expressed in heterologous background appeared to have
normal structure, since they were not affected in their ability to bind
different human plasma proteins. In particular, M5 or Emm22 had
normal ability to bind human complement inhibitors, a property that has
been implicated in phagocytosis resistance. Results similar to those
obtained with M5 and Emm22 were obtained in experiments with the M6 and
Emm4 proteins. Together, these data suggest that the surface expression
of M protein alone may not be sufficient to confer phagocytosis
resistance and consequently that strain-specific factors
other than M and Emm proteins may contribute to the ability of group A
streptococci to resist phagocytosis.
0019-9567/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Strain-Specific Restriction of the Antiphagocytic
Property of Group A Streptococcal M Proteins
*
Corresponding author. Mailing address: Institute for
Laboratory Medicine, Section for Microbiology, Immunology, and
Glycobiology, Sölvegatan 23, S-22362 Lund, Sweden. Phone:
46-46-173238. Fax: 46-46-189117. E-mail:
ulf.sjobring{at}mig.lu.se.
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