The toxicity of streptolysin O for beating mammalian heart cells in tissue culture

Streptolysin O II. Relationship of Sulfyhdryl Groups to Activity

Streptolysin O (SO), a group A streptococcal toxin, exists in two forms, a reduced active state and an oxidized reversibly inactive state. Activity is measured by red blood cell hemolysis. SO is a labile toxin, and, with time, activity is irreversibly lost. The rate of activity loss is slowed by incubation with 0.1 m 2-mercaptoethanol or 0.01 m ethylenediaminetetraacetic acid (EDTA). The effect of EDTA can be reversed by excess MgSO(4). Reversibly oxidized SO is activated by cleavage of disulfide bonds. When the free sulfhydryl groups of the active SO are alkylated with iodoacetamide, complete and irreversible loss of activity results. Periodate (0.01 m) oxidation also causes complete loss of activity which may be due to oxidation of sulfhydryl groups. SO in the active form reacts with Fe(2+), Cu(2+), Ca(2+), and Mg(2+), causing loss of activity in various degrees depending on the ions and the concentration used. Ferric and cupric ions are most effective and cause loss of activity at concentrations on the order of 10(-4)m. The reversibly oxidized form of SO is not influenced by exposure to cupric ions (0.01 m), indicating that the reaction is only with the active form of SO, probably involving the free sulfhydryl groups. These groups may be responsible for the direct binding of the toxin to the target membrane or for the maintenance of the proper conformation for activity.

Comparison of pathogenic factors expressed by group A Streptococci isolated from patients with streptococcal toxic shock syndrome and scarlet fever

Streptococcal toxic shock syndrome (STSS) is an illness with high mortality. To obtain clues to understanding the pathogenesis of STSS, we investigated the expression of several pathogenic factors in ten group A streptococcus (GAS) isolates from ten patients with STSS in Japan, in comparison with ten GAS isolates from children with scarlet fever. The ten scarlet fever-derived GAS isolates were equally low in lethality and anti-phagocytic activity in mice and in the production of streptolysin O (SLO), and equally high in production of superantigenic exotoxins (SAGTs) and cysteine proteinase. By comparison, the ten STSS-derived GAS isolates were heterogeneous in the expression of the above pathogenic factors, which ranged from low to high values. Most of the ten STSS-derived isolates were higher in lethality and anti-phagocytic activity and production of SLO, and lower in the production of SAGTs and cysteine proteinase than the ten scarlet fever-derived isolates. The results suggest that the lethality and anti-phagocytic activity examined in mice and SLO may be involved mainly in the development of most of the ten STSS cases.

Coronary vasoconstriction is the most probable cause of death of rats intoxicated with botulinolysin, a hemolysin produced by Clostridium botulinum

The pathophysiology of lethal intoxication by botulinolysin (Blyn) was studied using anesthetized rats and isolated rat organs. Intravenous injection of 10,000 and 1000 hemolytic units (HU) of Blyn killed rats rapidly while 100 HU of the toxin did not. Congestion and edema of lungs were observed at autopsies of the rats killed by intoxication. Hemoglobinemia was obvious in rats injected with 1000 HU of Blyn but not in rats with 10,000 HU. Electrocardiograms of the intoxicated rats showed depression of T waves but not changes characteristic of hyperpotassemia. All the rats injected with the above doses of Blyn showed a rapid fall in arterial blood pressure (BP) immediately after the toxin injection, and BP soon recovered in rats injected with 100 HU, partially and transiently in rats with 1000 HU, and not in rats with 10,000 HU of Blyn. Perfusion of Blyn (1 HU/ml) to isolated rat hearts caused a rapid and marked increase in perfusion pressure and cessation of spontaneous heart beat. Acetylsalicylic acid (10(-3) M) and quinacrine dihydrochloride (10(-5) M) did not essentially influence the effects of Blyn on the isolated hearts, but verapamil (10(-6) M) inhibited at least the initial increase in perfusion pressure elicited by Blyn. Spontaneous contractions of the isolated atria were little influenced by Blyn (60 HU/ml). Perfusion pressures of isolated kidneys, lungs and livers were also increased by Blyn (1 HU/ml). The results indicate that Blyn caused vasoconstriction but had little direct effect on myocardium. Based on the above findings, we conclude that coronary vasoconstriction elicited by direct action of Blyn causes acute cardiac dysfunction leading to systemic hypotension and death of the intoxicated animals.

Assessment of antibody mediated cytolysis of adult cardiocytes isolated by centrifugation in a continuous gradient of Percoll in patients with acute myocarditis

Principal objections to conventional cytotoxicity assays in cardiac disease with myocytes as target cells are the use of fetal or neonatal myocardium, the cell-membrane of which does not express all antigenic determinants, and the use of trypsin as enzyme for isolation of the cells, since this alters the myolemmal membrane considerably. An improved and rapid procedure for the isolation of intact adult cardiocytes with collaggenase was developed. by means of a performed continuous self-generating silica sol and gradient centrifugation average enrichment of 81% vital myocytes was achieved by a single isopycnic procedure. The yield was improved to 94 +/- 3% vital cells by identical second centrifugation. Cardiocytes isolated by this method were used as target cells in an assay measuring the cytolytic activity of antibodies in the presence of complement: sera of patients suffering from acute viral myocarditis (Coxsackie B- and influenza-virus) with complement fixing antisacrolemmal antibodies (ASA) of the IgG- and IgM-type showed significant cardiocytolysis. ASA are postulated to play a role in the pathogenesis of acute Coxsackie B- and influenza-virus myocarditis.

Suppression of the antistreptolysin O response by cholesterol and by lipid extracts of rabbit skin

Lipids extracted from rabbit skin block the hemolytic capacity of SO and also suppress the neutralizing antibody response to this streptococcal extracellular antigen in rabbith immunized intravenosly. The modification in antibody response is specific for SO; the antibody responses to streptococcal DNase B and to streptococcal NADase are not affected. Cholesterol, a lipid present in abundance in skin, has a similar specific effect on the antigenicity of SO and may be the component responsible for the demonstrated effects of these lipid extracts of skin. In vitro experiments indicate that lipid extracts of rabbit skin have a greater capacity to block the hemolytic capacity of SO than do lipid extracts of rabbit heart, kidney, lung, liver, or spleen. These data support the view that the feeble ASO response observed in patients with streptococcal pyoderma is a result of the abundance of a local lipid inhibitor, such as cholesterol, in the skin. They may also bear on the pathogenesis of rheumatic fever, a complication which apparently does not occur following group A streptococcal pyoderma. Two possible explanations for this remarkable epidemiologic observation, both related to the presence of a local inhibitor, are considered: (a) suppression of the ASO response, the magnitude of which has been correlated with the risk of developing rheumatic fever after streptococcal infection of the throat, and (b) inhibition of the toxicity of SO, which has been shown to have a direct toxic effect on the mammalian heart and on isolated beating myocytes.

Two previously undescribed extracellular streptococcal antigens detectable with naturally occurring human antibodies

Two streptococcal extracellular antigens (X and Y), which are detectable with naturally occurring human antibodies, have been isolated and shown to represent entities distinct from previously described streptococcal enzymes, toxins, and antigens. They are each synthesized by both group C and group A streptococci and appear to be proteins. Both antigens were found to be nonhemolytic and nontoxic for human leucocytes as well as for isolated beating newborn rat heart cells in tissue culture. In addition to being distinct from known streptococcal enzymes, they were also shown to be devoid of several other enzymatic activities.

Oxygen-stable hemolysins of group A streptococci. 8. Leukotoxic and antiphagocytic effects of streptolysins S and O

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.

In vitro organization of dissociated rat cardiac cells into beating three-dimensional structures

When isolated beating ventricular heart cells from newborn rats were grown in tissue culture on untreated polystyrene surfaces, they showed a striking tendency to grow focally in three dimensions from the single layer cell sheets which were formed early in growth. During this process, they frequently formed miniature spherical heart-like masses, which continued to beat and grow in size. These often were somewhat lobulated in appearance, and grew up to 2 mm in diameter. Histological sections of such structures sometimes revealed evidence of appreciable orientation of the cells to each other, in fiber-like units. Electron microscope sections of such mini-hearts showed structures resembling intercalated discs between myocardial cells. The precise factors which induced the cardiac cells to apparently organize into these heart-like structures are not presently known.