Rabbits injected intravenously with extracellular products ("toxins") of group A streptococci develop myocardial, muscular, and hepatic lesions. When such animals are then challenged with fluorochrome-labeled group A streptococci or with titanium oxide particles the labeled bacteria or particles localize within phagocytic cells in the tissue lesions caused by the toxins. Similarly, labeled streptococci or titanium oxide particles will also localize within phagocytic cells in skin lesions of guinea pigs that develop delayed hypersensitivity to tuberculin or to bovine gamma globulin. It is proposed that a combined mechanism of injury and localization of bacteria in damaged tissues may be responsible for poststreptococcal sequelae or other chronic inflammatory diseases.

Studies on the host parasite relationship in experimental streptococcal infections have been greatly aided by fluorescent antibody techniques (1). By such methods it is possible to follow the localization and persistence of group A streptococcal antigen in cells and tissues of laboratory animals (2-6). To detect such antigens by fluorescent techniques, frozen sections are often employed and the antisera to streptococcal antigens must be repeatedly absorbed with organ powders to remove nonspecific staining. The present communication describes a simple method for applying a label of fluorescein isothiocyanate (FITC) to living group A streptococci, streptococcal cell-wall fragments,mucopeptides, and streptococcal Lforms. Such labeled streptococci and products were found to persist for long periods of time in inflammatory sites in the muscle and heart of mice and rabbits.