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Variable Susceptibility to Opsonophagocytosis of Group A Streptococcus M-l Strains by Human Immune Sera

A. Villaseñor-Sierra, W. M. McShan, D. Salmi, E. L. Kaplan, D. R. Johnson and D. L. Stevens
The Journal of Infectious Diseases
Vol. 180, No. 6 (Dec., 1999), pp. 1921-1928
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/30109229
Page Count: 8
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Variable Susceptibility to Opsonophagocytosis of Group A Streptococcus M-l Strains by Human Immune Sera
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Abstract

Immunity to group A streptococci (GAS) is thought to be related to the acquisition of type-specific antibody directed against the M protein. However, recent work suggests that immunity may only be strain and not M-type specific. Therefore, susceptibility of 70 different GAS M1 strains to opsonization and killing by convalescent sera was compared by using a highly sensitive chemiluminescence assay and by standard bactericidal assay. Sequencing of the emm\ gene in 10 strains with variable susceptibility to opsonization revealed 100% homology in 9 strains. Several substitutions in the N-terminal and 2 in the A3 repeat regions of strain CS190 were associated with profound resistance to opsonization. Thus amino acid substitutions within different regions of the M-l protein molecule may adversely affect opsonization by immune sera. In addition, non-M protein factors from identical M types influence susceptibility to phagocytosis. These findings may in part explain the persistently high prevalence of M-l strains worldwide over the last 15 years.

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