Although numerous epidemiological and clinical studies have shown a definite relationship between a previous infection with strains of Group A streptococci and the appearance of sequelae (rheumatic fever, arthritis, nephritis), the mechanisms which lead to their development are still not fully understood. Since man is the only animal species which suffers from natural infections with Group A streptococci, and since it is agreed that viable streptococci cannot usually be isolated from the lesions characteristic of the chronic complications, Koch’s postulate can at best incriminate these micro-organisms only in the etiology of the acute infections but not in their subsequent complications. Despite many attempts to duplicate rheumatic fever, arthritis and acute glomerulonephritis in laboratory animals including higher apes, as a rule, the tissue lesions which developed in some of the animals bore little resemblance to the human lesions, and no true duplication of a disease syndrome similar to that seen in human beings has been reported. Two major theories have been proposed by various investigators to explain the nature of poststreptococcal complications. One theory proposes that the toxic effects of some streptococcal products (streptolysins O and S, erythrogenic toxin, proteinase, cell-wall mucopeptide-polysaccharide complex) are responsible for the initiation of the chronic lesions in the heart, joint and kidney characteristic of poststreptococcal diseases. The second theory suggests that the immunopathological phenomena (immune complex disease, cross-reactive immunity, delayed hypersensitivity) which develop in certain pa- tients who have become sensitized to one or more of the streptococcal products are responsible for the initiation of the disease in man. These two hypotheses are not, of course, mutually exclusive. Although no unified theory has been advanced which adequately explains the nature of the various post- streptococcal complications, a combination of both views may fit many, if not all, the features characteristic of these sequelae. Some theories on the pathogenesis of human poststreptococcal diseases and on the mechanisms of tissue injury induced by Group A streptococci have been recently reviewed (Taranta and Uhr, 1971; Ginsburg, 19720, b). The purpose of this paper is to describe some of the mechanisms by which Group A streptococci localize and persist in mammalian tissues and to relate the experimental models to the pathogenesis of poststreptococcal sequelae in man.

The cell-sensitizing factor (SF) of group A streptococci is a teichoic acid which can sensitize mammalian cells to agglutination and lysis in the presence of anti ·SF antibodies and complement. SF is highly immunogenic in the rabbit when bound naturally to some constituent of the streptococcus cell, but only feebly so when it is extracted from the cells by phenol. Both rabbit and human antibodies to SF, which are mainly associated with the macroglobulin fraction (IgM) of serum, are destroyed by treatment with 2-mercaptoethanol. While human anti-SF antibodies are readily destroyed by freezing and thawing and by heating to 58 C, the rabbit anti-SF antibodies are not destroyed at 64 C and are relatively resistant to repeated freezing and thawing. Complexes formed between SF and rabbit antibodies fix complement both in the absence and presence of red blood cells (RBC). Anti-SF antibodies interact with SF and prevent the latter from sensitizing RBC. Rabbits immunized with heat-killed streptococci and which developed anti-SF antibodies, developed severe arthritis when SF was injected into their knee joints. The arthritic lesions were characterized by a marked proliferation of the synovial membrane, a chronic inflammatory exudate and the accumulation of large numbers of lymphocytes in the form of "pseudolymphatic follicles." Nonimmunized animals failed to develop such lesions. It is suggested that sensitization of cells with SF during streptococcal infection may lead to passive immune cytolysis and may thus contribute to the pathogenicity of streptococci.

Earlier reports had described the presence, in supernates of streptococcal steady-state cultures, of a macromolecular toxin which causes infiltrative and necrotic lesions in the heart and liver of rabbits and changes in the serum level of certain enzymes and lipids. In the present study, following treatment of the culture supernate concentrates with trichloroacetic acid and ethanol, and dialysis, material with these biologic activities has been found, in the dialysate, and was not excluded by Sephadex G-15. The molecular weight of the toxin, by this criterion, is near that of vitamin B12.

Streptolysin S exists in a cell-bound form and as an extracellular complex between a nonspecific carrier (serum, serum albumin, ribonucleic acid [RNA], Triton, Tween) and a hemolytic moiety (probably a peptide) synthesized by streptococci. Although all the forms of streptolysin S, at 100 hemolytic units, killed mouse leukocyte monolayers, the time needed to kill 100% of the cells varied with the different streptolysin S preparations. Whereas 30 min was sufficient for the cell-bound hemolysin to kill all of the cells, 60 and 180 min were required when RNA streptolysin S and serum streptolysin S, respectively, were employed. Addition of 10% mouse serum to RNA streptolysin S or to cell-bound hemolysin delayed the killing of the leukocytes. The delayed killing observed with serum and albumin hemolysins is probably due to competition for the hemolytic moiety between the carrier molecules and target sites (phospholipids) upon the leukocyte membrane. Serum streptolysin S must be constantly incubated with the cells for 90 min for 100% of the cells to undergo cytopathic changes upon subsequent incubation for an additional 90 min. Streptolysin S inhibitor (trypan blue) added to the system after 30 or 60 min of incubation resulted in the killing of 50 and 100% of the leukocytes, respectively, when the cells were further incubated for 120 min. It is suggested that 30 min of incubation was not sufficient for the transfer of enough streptolysin S molecules upon the cell surface to allow killing of all of the cells. Sublethal amounts of streptolysin S, streptolysin O, and saponin suppressed phagocytosis of streptococci by mouse peritoneal macrophages. This effect was abolished by inhibitors of streptolysin S (trypan blue) and of streptolysin O and saponin (cholesterol). With sublethal amounts of streptolysin S, no inhibition of the reduction of nitro blue tetrazolium by nonphagocytosing cells was observed, but these amounts of streptolysin S caused a 50% inhibition of the reduction of nitro blue tetrazolium by phagocytosing leukocytes. It is suggested that some metabolic systems, which are normally enhanced during phagocytosis, have been affected by sublethal doses of streptolysin S. The results indicate that the in vivo production of small amounts of streptolysins S and O by group A streptococci may inhibit phagocytosis and may thus contribute to the invasiveness and pathogenicity of this microorganism.