Experimental arthritis induced by atypical strains of Streptococcus pyogenes.

Experimental arthritis was induced in Sprague-Dawley rats by intraarticular injection of whole-cell sonicates, heat-killed cells and cell-wall preparations of typical and atypical strains of Group-A streptococci (Streptococcus pyogenes). The non-haemolytic nitrosoguanidine-derived mutant and the naturally occurring Lowry strain induced a similar but less severe form of arthritis. Direct immunofluorescent staining demonstrated maximum fluorescence in the sections of articular joint taken 60 days after injection. The level of immune complexes increased for up to 90 days after injection of cell walls or whole-cell sonicates and correlated well with the development of the chronic stage of arthritis observed in haematoxylin and eosin and fluorescence staining of thin tissue sections.