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Variable susceptibility to opsonophagocytosis of group A streptococcus M-1 strains by human immune sera

A Villaseñor-Sierra1, W M McShan, D Salmi

  • 1Centro de Investigacion Biomedica de Occidente (CIBO), Instituto Mexicano del Seguro Social, Guadalajara, Mexico.

The Journal of Infectious Diseases
|November 24, 1999
PubMed

Insights

Immunity to group A streptococci (GAS) depends on antibodies to M protein, but strain-specific factors also impact opsonization and killing. Amino acid changes in M-1 protein can cause resistance to immune sera.

Area of Science:

  • Microbiology
  • Immunology
  • Infectious Diseases

Background:

  • Immunity to group A streptococci (GAS) is traditionally linked to type-specific antibodies against the M protein.
  • Emerging evidence suggests that immunity might be strain-specific rather than solely M-type specific.

Purpose of the Study:

  • To investigate the susceptibility of diverse GAS M-1 strains to opsonization and killing by convalescent sera.
  • To identify genetic and molecular factors influencing GAS resistance to host immune responses.

Main Methods:

  • Utilized a sensitive chemiluminescence assay and standard bactericidal assays to compare opsonization and killing of 70 GAS M-1 strains.
  • Sequenced the emm1 gene of 10 strains exhibiting variable opsonization susceptibility.

Main Results:

  • Identified significant variability in opsonization susceptibility among GAS M-1 strains.
  • Found 100% homology in the emm1 gene for 9 out of 10 strains, with strain CS-190 showing substitutions linked to opsonization resistance.
  • Demonstrated that amino acid substitutions in the M-1 protein and non-M protein factors influence phagocytosis resistance.

Conclusions:

  • Amino acid variations within the M-1 protein can impair opsonization by immune sera.
  • Non-M protein factors contribute to phagocytosis resistance in GAS strains of the same M type.
  • These factors may explain the sustained prevalence of M-1 strains globally.

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