VARIATION OF MULTIFUNCTIONAL SURFACE BINDING-PROTEINS - A VIRULENCE STRATEGY FOR GROUP-A STREPTOCOCCI

Variation in surface antigens has been well recognized as a mechanism by which pathogenic organisms can avoid elimination and remain as pote ntial pathogens in immunocompetent individuals. A variety of viral and parasitic organisms elude the immune system by varying their surface antigenic structures. Other persistent human pathogens, for example gr oup A streptococci, are associated with cyclic variation in the severi ty of infections without any major change in their surface antigenic s tructures. Recent analysis of group A streptococcal proteins, in parti cular surface M and M-like proteins, has documented the existence of a n array of multifunctional surface proteins which have the ability to bind to a variety of normal human plasma proteins, extracellular matri x components and human cells. The ability to change the functional act ivities of these surface molecules by genetic recombination among memb ers of a closely related M protein supergene family has now been repor ted. In this paper, the potential importance of generating functional heterogeneity in surface binding proteins of group A streptococcus is discussed. The role of these proteins in enabling an organism to sense its environment and express the appropriate virulence factors is prop osed as an explanation for the periodic changes in the frequency and s everity of invasive group A streptococcal infections that can occur in the absence of a toxic-shock-like syndrome.