Oral streptococci show diversity in resistance to complement immunity

Area of Science:

• Microbiology
• Immunology
• Oral Health

Background:

• Commensal oral streptococci, including Mitis and Sanguinis groups, can cause systemic infections.
• Mechanisms by which these bacteria evade host immune responses are not well understood.

Purpose of the Study:

• To investigate the susceptibility of oral Mitis and Sanguinis streptococci to complement-mediated immunity.
• To compare immune evasion strategies between oral commensal strains and those causing systemic infections.

Main Methods:

• Quantified complement opsonin deposition (C3b/iC3b) and binding to C-reactive protein (CRP) and IgG using flow cytometry.
• Assessed opsonophagocytosis by human neutrophils mediated by complement and/or Fc receptors.

Main Results:

• Streptococcus sanguinis strains exhibited lower complement opsonization and reduced binding to CRP and IgG compared to other species.
• Strains of Streptococcus gordonii and Mitis groups isolated from systemic infections showed greater resistance to complement opsonization than oral isolates.
• Complement deposition correlated with opsonophagocytosis in Mitis species.

Conclusions:

• Established species-specific susceptibility profiles to complement immunity for Mitis and Sanguinis streptococci.
• Demonstrated that strains causing systemic infections possess enhanced mechanisms for evading complement immunity.
• Highlighted the need to identify molecular factors involved in complement evasion by oral streptococci.