Cross-reactivity between streptococcal M surface antigen and human skin

Area of Science:

• Immunodermatology
• Microbial Pathogenesis
• Structural Biology

Background:

• Psoriasis can be initiated by hemolytic streptococcal infections.
• Streptococcal M protein is a key surface antigen involved in pathogenicity.
• Investigating cross-reactivity between M protein and human epidermis is crucial for understanding post-streptococcal psoriasis.

Purpose of the Study:

• To investigate the cross-reactivity between streptococcal M protein and human epidermal components.
• To explore the structural basis for potential molecular mimicry between M protein and keratin.
• To assess the relevance of these cross-reactivities in the pathogenesis of psoriasis.

Main Methods:

• Computer-assisted analysis comparing the amino acid sequence of M protein (M6) with human proteins in a data bank.
• Analysis of conserved alpha-helical 'coiled-coil' configurations in M protein and human keratin.
• Immunohistochemical staining of skin sections using antisera raised against various M proteins.

Main Results:

• Protein M6 showed significant homology with 50-kDa keratin type 1, particularly in heptapeptide repeat patterns forming alpha-helical structures.
• M protein antisera reacted with the stratum corneum of normal and psoriatic epidermis.
• Cytoplasmic staining of keratinocytes was more prominent in lesional psoriatic skin; dendritic cells, endothelium, and smooth muscle also showed reactivity.

Conclusions:

• Structural similarities between streptococcal M protein and human keratin suggest a mechanism for molecular mimicry.
• Observed cross-reactivities between M proteins and skin components may contribute to the pathogenesis of post-streptococcal psoriasis.