Specificity of diphtheria toxin action on heart and muscle tissues of Guinea pigs

Heart and muscle tissues appear to be specific target organs for the in vivo inhibition of protein synthesis by diphtheria toxin.

Uptake of h-dihydrostreptomycin by macrophages in culture

Mouse peritoneal macrophages, in culture, concentrate significant amounts of (3)H-dihydrostreptomycin, provided that the incubation period is sufficiently extended. Macrophages cultured in vitro from both stimulated and unstimulated animals concentrate the antibiotic from growth or maintenance media. The increase in cell-associated radioactivity is linear for almost a week before a plateau is reached. Calculations based on intracellular volumes of the cells indicate that the intracellular concentration of dihydrostreptomycin may attain levels greater than five times that of the external milieu. No uptake is measurable at 4 C, suggesting an active mechanism of transport into the cell. Phagocytosis of killed bacteria during incubation did not increase uptake of the antibiotic nor did the addition of poly-l-ornithine to the medium augment uptake. A nonphagocytic cell line (BHK-21) concentrated (3)H-dihydrostreptomycin to a lesser extent than the macrophages. These observations suggest that a wide variety of mammalian cells may be permeable to the antibiotic, and thus potential bactericidal action on intracellular bacteria cannot be ignored.

Crystal structure of a biologically inactive mutant of toxic shock syndrome toxin-1 at 2.5 A resolution

Toxic shock syndrome toxin-1 (TSST-1) is one of a family of staphylococcal exotoxins recognized as microbial superantigens. The toxin plays a dominant role in the genesis of toxic shock in humans through a massive activation of the immune system. This potentially lethal illness occurs as a result of the interaction of TSST-1 with a significant proportion of the T-cell repertoire. TSST-1, like other superantigens, can bind directly to class II major histocompatibility (MHC class II) molecules prior to its interaction with entire families of V beta chains of the T-cell receptor (TCR). The three-dimensional structure of a mutant (His-135-Ala) TSST-1 was compared with the structure of the native (wild-type) TSST-1 at 2.5 A resolution. The replacement of His 135 of TSST-1 with an Ala residue results in the loss of T-cell mitogenicity and toxicity in experimental animals. This residue, postulated to be directly involved in the toxin-TCR interactions, is located on the major helix alpha 2, which forms the backbone of the molecule and is exposed to the solvent. In the molecular structure of the mutant toxin, the helix alpha 2 remains unaltered, but the His to Ala modification causes perturbations on the neighboring helix alpha 1 by disrupting helix-helix interactions. Thus, the effects on TCR binding of the His 135 residue could actually be mediated, wholly or in part, by the alpha 1 helix.

A toxic shock syndrome toxin 1 mutant that defines a functional site critical for T-cell activation

Toxic shock syndrome toxin 1 (TSST-1), a superantigen produced by Staphylococcus aureus, is a causative agent of toxic shock syndrome (TSS). This superantigen is a potent stimulator of T cells and macrophages/monocytes, resulting in the release of cytokines that are implicated in the pathogenesis of TSS. This study characterizes a mutant TSST-1, derived by site-directed mutagenesis, that has an alanine substitution at histidine 135 (mutant 135). This single-amino-acid change results in a mutant toxin that has lost mitogenic activity for T cells. In contrast to wild-type TSST-1, this mutant does not induce T cells to express interleukin-2, gamma interferon, or tumor necrosis factor beta (TNF-beta). The inability of mutant 135 to activate T cells is not due to a lack of binding to the class II major histocompatibility complex receptor. In addition, the mutant TSST-1 does not induce expression of TNF-alpha, which plays a role in the development of lethal shock. The lack of TNF-alpha induction by mutant 135 is likely due to its inability to activate T cells. These data suggest that the mutation at histidine 135 in TSST-1 affects toxin interactions with the T-cell receptor rather than the class II major histocompatibility complex receptor.

Biological activity of toxic shock syndrome toxin 1 and a site-directed mutant, H135A, in a lipopolysaccharide-potentiated mouse lethality model

A recombinant of toxic shock syndrome toxin 1 (TSST-1) which contains a single histidine-to-alanine mutation at residue 135 (H135A) was analyzed for toxicity and vaccine potential in a lipopolysaccharide (LPS)-potentiated mouse lethality model. The 50% lethal dose (LD50) of TSST-1 in BALB/c mice was 47.2 micrograms/kg, but H135A was not lethal when tested at a dose equivalent to 10 LD50s of TSST-1. Levels of tumor necrosis factor (TNF) and gamma interferon (IFN-gamma) in serum were, respectively, 10- and 50-fold higher in LPS-potentiated mice injected with 15 LD50s of TSST-1 than in mice given H135A. Mice injected with only TSST-1 did not have elevated levels of TNF or IFN-gamma in serum, while H135A plus LPS or LPS alone elicited identical, yet very low, levels of TNF and IFN-gamma. An enzyme-linked immunosorbent assay of H135A and TSST-1 with anti-TSST-1 serum yielded very similar dose-response curves, which strongly suggests that H135A serologically and conformationally resembles the native toxin. Mice immunized with H135A developed antibodies that recognized TSST-1 in an enzyme-linked immunosorbent assay and afforded protection against a 15-LD50 challenge of TSST-1 plus LPS. The pooled sera of mice immunized with either TSST-1 or H135A also prevented lymphocyte proliferation due to TSST-1.

Role of a carboxy-terminal site of toxic shock syndrome toxin 1 in eliciting immune responses of human peripheral blood mononuclear cells

Staphylococcus aureus toxic shock syndrome toxin 1 (TSST-1) is involved in the pathogenesis of toxic shock syndrome and perhaps other staphylococcal diseases. Recently, the C-terminal part of the TSST-1 toxin has been shown to be responsible for mitogenic activity in animal models. We studied the role of the C-terminal structural unit of TSST-1 with regard to proliferation, cytokine release (tumor necrosis factor alpha [TNF-alpha], interleukin-6 [IL-6], and IL-8), mRNA expression for IL-6, IL-8, IL-10, TNF-alpha, and CD40 ligand (CD40L), synthesis of immunoglobulin E (IgE), IgA, IgG, and IgM, CD23 expression, and soluble CD23 (sCD23) release from human peripheral blood mononuclear cells (PBMC). For this purpose, we used the recombinant wild-type TSST-1 (p17) mutant toxin Y115A (tyrosine residue modified to alanine) and toxin H135A (histidine residue modified to alanine). Unmodified toxin p17 and mutant toxin Y115A, at a concentration below 5 ng, to a lesser degree, induced a strong proliferation. Toxin p17 followed by toxin Y115A was the most pronounced inducer for mRNA expression for IL-10 and CD40L and cytokine generation (mRNA and protein) for TNF-alpha, IL-6, and IL-8. Mutant protein H135A failed to activate human PBMC. Both toxins p17 and, to a lesser degree, Y115A significantly suppressed IL-4- and anti-CD40-induced synthesis of all four Igs as well as IL-4-induced CD23 expression and sCD23 release. Mutant toxin H135A failed to do so. Thus, our data show that a region in the C terminus of TSST-1 is responsible not only for mitogenic activity but also for additional immunomodulating biological activities of TSST-1. More specifically, histidine residue H135A of the 194-amino-acid toxin appears to be critical for the expression of biological activities in a human in vitro model.

A mutation at histidine residue 135 of toxic shock syndrome toxin yields an immunogenic protein with minimal toxicity

Structure-function studies have revealed that the region between amino acids 115 and 141 of toxic shock syndrome toxin 1 (TSST-1) constitutes a biologically active domain. A critical residue appears to be histidine 135, since a site-directed mutation that alters the histidine to alanine (H135A) results in a loss of mitogenic activity and an absence of toxicity as measured in a rabbit infection model of toxic shock syndrome. We have characterized the mutant toxin further and report here on its immunogenic activity in rabbits and on the protective ability of mutant-specific antibodies in two animal models of toxin-mediated shock. Antibodies raised in rabbits by immunization with the purified H135A are fully cross-reactive with staphylococcal TSST-1 and wild-type recombinant TSST-1 (rTSST-1) expressed in Escherichia coli. The H135A antibodies neutralized the mitogenic activity for murine splenic T cells equally well as did TSST-1-specific polyclonal and monoclonal antibodies. In addition, the H135A antibodies blocked the production of tumor necrosis factor by spleen cells stimulated with rTSST-1. The toxicities of rTSST-1 and H135A were compared in D-galactosamine (D-GalNH2)-sensitized MRL-lpr/lpr mice. The nontoxicity of H135A was confirmed in this murine model of superantigen-induced septic shock. No toxicity of H135A was demonstrable at doses of 60 micrograms, while doses of rTSST-1 as low as 2 micrograms caused significant mortality within 24 to 72 h after challenge. Furthermore, subsequent to challenge of mice with H135A, no elevation in the serum levels of interleukin-2 or tumor necrosis factor was measurable. Passive immunization with H135A antibodies also protected MRL-lpr/lpr mice against lethal challenge with rTSST-1. Finally, rabbits actively immunized with purified H135A did not succumb to infection with a transformed strain of Staphylococcus aureus expressing rTSST-1. Additional animal studies will be required to confirm the immunizing potential of H135A and the efficacy of H135A antibodies as a neutralizing antitoxin.

A fas antigen receptor mutation allows development of toxic shock syndrome toxin-1-induced lethal shock in V beta 8.2 T-cell receptor transgenic mice

Recombinant toxic shock syndrome toxin-1 (rTSST-1) administered to MRL-lpr/lpr TCR V beta 8.2 transgenic mice at doses of 0.1 microgram/mouse resulted in 100% mortality. This was an unexpected finding since TSST-1 does not activate V beta 8.2 T cells. In contrast, control mice heterozygous at the lpr locus and also for the transgene (MRL-lpr/+; V beta 8.2/0) survived doses of superantigen 100 times higher. The transgenic mice which succumbed to rTSST-1 challenge exhibited histopathology of the liver consistent with toxic shock (generalized inflammation and hepatocellular necrosis) as well as substantially elevated serum TNF-alpha, IL-2, and IL-6 cytokine levels. Splenic T cells derived from transgenic mice stimulated with rTSST-1 in vitro did not undergo detectable proliferation as measured in a standard mitogen assay. However, PCR amplification of cDNA prepared from the V beta 8.2 splenocytes revealed the presence of minor populations of TSST-1-reactive V beta elements (i.e. V beta 3 and V beta 15). Furthermore, an expansion of the V beta 3 and V beta 15 T-cell families was detected by PCR assay of spleen cell cultures stimulated with rTSST-1. These results suggested that the exquisite sensitivity of the MRL-lpr/lpr V beta 8.2 transgenic animals to rTSST-1 was not dependent exclusively on T-cell proliferation but was augmented by the influence of a defective fas antigen receptor expressed in homozygous lpr mice. To test this hypothesis more directly, we compared the sensitivity of MRL-lpr/lpr mice (not carrying the V beta 8.2 transgene) to MRL-+/+ mice. The MRL-lpr/lpr fas antigen-defective mice were substantially more susceptible to rTSST-1 challenge. Mice carrying the lpr mutation on another genetic background (C57BL/6.C3H-lpr/lpr) were also more sensitive to rTSST-1 challenge than were C57BL/6.C3H-+/+ mice. Although induction of toxic shock is clearly associated with T-cell proliferation, defects in fas antigen receptor or ligand may also contribute substantively to superantigen-mediated lethal shock by still undefined mechanisms.

Toxicity of recombinant toxic shock syndrome toxin 1 and mutant toxins produced by Staphylococcus aureus in a rabbit infection model of toxic shock syndrome

Menstrually associated toxic shock syndrome (TSS) is attributed primarily to the effects of staphylococcal exotoxin toxic shock syndrome toxin 1 (TSST-1). A region of the 194-amino-acid toxin spanning residues 115 through 144 constitutes a biologically active site. Several point mutations in the TSST-1 gene in that region result in gene products with reduced mitogenic activity for murine T cells. In this study we evaluated the toxicity of recombinant TSST-1 and several mutants of TSST-1 made by transformed Staphylococcus aureus during in vivo growth in a rabbit infection model of TSS. The toxicities of the transformed strains of S. aureus for rabbits correlated with the mitogenic activities of the recombinant toxins. An isolate originally obtained from a patient with a confirmed case of TSS (S. aureus 587) implanted in a subcutaneous chamber served as a positive control. TSST-1 produced in vivo led to lethal shock within 48 h, and a TSST-1-neutralizing antibody (monoclonal antibody 8-5-7) administered to rabbits challenged with S. aureus 587 prevented fatal illness. Rabbits infected with transformed S. aureus RN4220 expressing wild-type toxin (p17) or mutant toxins retaining mitogenic activity for T cells succumbed within a similar time frame. Blood chemistries of samples obtained from infected animals before death indicated abnormalities in renal and hepatic functions similar to those induced by parenteral injection of purified staphylococcal TSST-1. Mutant toxin 135 (histidine modified to alanine at residue 135) possessed only 5 to 10% of the mitogenic activity of wild-type toxin. Rabbits challenged with transformed S. aureus RN4220 expressing mutant toxin 135 exhibited only mild transient illness. Mutant toxin 135 retained reactivity with monoclonal antibody 8-5-7 and by several criteria was conformationally intact. Toxin from a double mutant, 141.144, with alanine substitutions at residues 141 (histidine) and 144 (tyrosine), also was devoid of mitogenic activity. In this case, antibody recognition was lost. Mutant toxins 115 and 141 were found to possess approximately half-maximal mitogenic activity. Rabbits challenged with S. aureus RN4220 expressing either 115 or 141 toxin succumbed to lethal shock. We conclude that the ability of TSST-1 to activate murine T cells in vitro and its expression of toxicity leading to lethal shock in rabbits are related phenomena.

Activation of in vitro proliferation of human T cells by a synthetic peptide of toxic shock syndrome toxin 1

A 21-mer synthetic peptide (KGEKVDLNTKRTKKSQHTSEG), designated TSST-1(58-78), was constructed from the primary structure of the toxic shock syndrome toxin 1 (TSST-1). The peptide reacted with a panel of neutralizing monoclonal antibodies (MAbs) to whole TSST-1 in solid-phase immunoassays. TSST-1(58-78) promoted the in vitro proliferation of human peripheral blood mononuclear cells (PBMC) in a dose-dependent manner. Minimum dose required for stimulation (P less than or equal to .05 microM) was 0.75 microM peptide. This mitogenic effect was abrogated by incubation of the peptide with MAbs to whole TSST-1 before addition to PBMC. The ability of TSST-1(58-78) to stimulate the proliferation of highly purified resting human T cells was analyzed. Significant proliferation (P less than or equal to .01) was observed only in the presence of increasing populations of monocytes added to the cultures. Adherent human monocytes exposed to TSST-1(58-78) released tumor necrosis factor. Thus, some of the immunoregulatory properties attributed to TSST-1 are demonstrated by the region of the toxin represented by the peptide TSST-1(58-78).

Cyclosporin A treatment converts Leishmania donovani-infected C57BL/10 (curing) mice to a noncuring phenotype

Cyclosporin A prevents visceralization of Leishmania major infection of BALB/c mice (N. C. Behforouz, C. D. Wenger, and B. A. Mathison, J. Immunol. 136:3067-3075, 1986; W. Solbach, K. Forberg, E. Kammerer, C. Bogdan, and M. Rollinghoff, J. Immunol. 134:702-707, 1986). We report that cyclosporin A exacerbates disseminated leishmaniasis caused by L. donovani in C57BL/10 mice. Normal mice challenged with 5 x 10(6) amastigotes intravenously cleared the infection within several months by spontaneous acquisition of cell-mediated immunity. In contrast, cyclosporin A administered daily intraperitoneally at a dose of 1.25 mg per mouse prevented development of curative immunity and converted C57BL/10 (curing) mice to a noncuring phenotype. A rationale for the contrasting effects of cyclosporin A in the two murine models of leishmaniasis is provided.

Mutants of staphylococcal toxic shock syndrome toxin 1: mitogenicity and recognition by a neutralizing monoclonal antibody

Toxic shock syndrome toxin 1 (TSST-1), a 22-kilodalton protein made by strains of Staphylococcus aureus harboring the chromosomal toxin gene, may elicit toxic shock syndrome in humans. In vitro, TSST-1 induces T cells to proliferate and macrophages to secrete interleukin-1. To conduct a structure-function analysis, point mutations on the TSST-1 gene were generated by site-directed mutagenesis to identify amino acids critical for activity of the toxin. Specific tyrosine and histidine residues were replaced by alanines. Wild-type and mutant TSST-1 gene constructs were expressed in Escherichia coli, and the products were tested for their mitogenic potential and reactivity with a TSST-1 neutralizing monoclonal antibody (MAb 8-5-7). Four of the mutants were similar to the wild type; i.e., the mutant toxins stimulated murine T cells and reacted with MAb 8-5-7 equally as well as the wild type. Two mutants exhibited a decrease in mitogenic activity, but one of these retained the capacity to bind with MAb 8-5-7 while the other was no longer recognized by the same antibody. One double mutant demonstrated minimal mitogenic activity and did not react in enzyme-linked immunosorbent and immunoblot assays with MAb 8-5-7. The data show that specific residues near the carboxy terminus of TSST-1 are essential for mitogenic activity and in forming the epitope recognized by neutralizing MAb 8-5-7.

Passive protection of rabbits infected with toxic shock syndrome-associated strains of Staphylococcus aureus by monoclonal antibody to toxic shock syndrome toxin 1

The effectiveness of passive immunization was assessed in an infection model of toxic shock syndrome (TSS) in which monoclonal antibody to TSS toxin 1 (TSST-1) was administered intravenously to rabbits. Previously implanted infection chambers were inoculated with Staphylococcus aureus strains RN4710 and D4508. The former strain carries the TSST-1 gene on plasmid pRN6201; the latter is a TSST-1-negative clinical isolate obtained from a patient with nonmenstrual TSS. Purified monoclonal antibody, MAb 8-5-7 (IgG), was administered in two doses of approximately 1.25 mg each 24 hours before and 24 hours after infection. MAb 8-5-7 provided complete protection against both the TSS-like syndrome and the mortality that occurred in unprotected rabbits infected with strain RN4710 but did not provide complete protection in rabbits infected with strain D4508; three of the five rabbits either displayed signs of illness or died despite treatment. Western-blot analyses of the extracellular proteins produced by strains RN4710 and D4508 that used MAb 8-5-7 as a probe revealed that only TSST-1 produced by RN4710 reacted with the antibody. Thus, if MAb 8-5-7 partially protected animals against infections with strain D4508, the protection appears to have been nonspecific.

Distribution and expression of toxic shock syndrome toxin 1 gene among Staphylococcus aureus isolates of toxic shock syndrome and non-toxic shock syndrome origin

Toxic shock syndrome toxin 1 (TSST-1), plays a significant role in the pathogenesis of TSS. TSST-1 production is subject to physiologic and environmental constraints. Thus, DNA probes that detect the chromosomal gene encoding the toxin are of value diagnostically, epidemiologically, and for studies of gene expression. Several synthetic oligonucleotide probes complementary to two regions of the TSST-1 gene were used to ascertain the presence of this gene in the chromosomal DNA of 261 strains of S. aureus from various TSS-related and non-TSS-related sources. Isolates were from clinically confirmed menstrual and nonmenstrual cases of TSS and from healthy vaginal carriers of S. aureus. Other strains tested included clinical non-TSS isolates and food poisoning-associated staphylococcal isolates. Detection of the TSST-1 gene by the labeled gene probes correlated in all but two cases with production of TSST-1. Ten Centers for Disease Control (CDC) strains that were isolated from TSS patients and did not produce TSST-1 were also examined, as were several strains of Staphylococcus epidermidis isolated from patients with suspected TSS. Neither group of strains possessed the TSST-1 gene. Finally, a 7-kilobase DNA restriction fragment of S. aureus containing the entire TSST-1 gene was transformed into Escherichia coli strains HB101 and DH5 alpha via a plasmid vector.

Endotoxin enhancement of toxic shock syndrome toxin 1-induced secretion of interleukin 1 by murine macrophages

The purpose of this study was to determine whether endotoxin could augment toxic shock syndrome toxin 1 (TSST-1)-induced production of interleukin 1 (IL-1) by murine macrophages. Macrophages from C3H/HeJ or C57Bl/6 mice were stimulated with purified TSST-1 alone or in combination with lipopolysaccharide (LPS). A dramatic synergistic thymocyte-proliferative response was induced by supernatants from C57Bl/6 macrophages stimulated with both TSST-1 and LPS. No enhanced response was induced by supernatants from C3H/HeJ macrophages. A portion of the enhanced response induced by C57Bl/6 macrophage supernatants was attributed to synergism between IL-1 and residual TSST-1 in the thymocyte assay. The addition of monoclonal antibody to TSST-1 to the supernatants eliminated the effects of residual TSST-1 in the thymocyte assay and demonstrated a synergistic induction of IL-1. These data (1) show that LPS can enhance macrophage responsiveness to TSST-1; (2) suggest that TSST-1 not only induces IL-1 secretion but also enhances target cell responsiveness to IL-1; and (3) further support the role of IL-1 in the pathogenesis of toxic shock syndrome.

Enhanced phagocytosis, killing, and serum sensitivity of Escherichia coli and Staphylococcus aureus treated with sub-MICs of imipenem

The influence of pretreatment of Escherichia coli and Staphylococcus aureus with sub-MICs of the new beta-lactam antibiotic imipenem on phagocytosis and killing by murine peritoneal macrophages and the susceptibility of these organisms to serum bactericidal activity were studied. The effects of imipenem, a round form inducer in gram-negative rods, and piperacillin, a filamentous form inducer, were compared. Bacteria grown in the presence of sub-MICs of imipenem or piperacillin were incubated for 30 min with macrophage monolayers in the absence of antibiotic. Phagocytosis, killing, and survival within macrophages were evaluated by microbiological and fluorescence microscope assays. Bacteria grown in the presence of a sub-MIC of imipenem were phagocytized and killed in numbers significantly higher than untreated or piperacillin-treated bacteria were. Intracellular bacteria pretreated with a sub-MIC of imipenem were also readily killed by lymphokine-activated macrophages. Prior treatment with a sub-MIC of imipenem resulted in an increased susceptibility of E. coli but not S. aureus to the bactericidal activity of immune serum. Imipenem treatment and immune serum acted synergistically to enhance phagocytosis and killing. The data indicate that exposure of E. coli and S. aureus to a sub-MIC of imipenem enhances the susceptibility of these potential pathogens to cellular and humoral host defense mechanisms.

Protection of rabbits in an infection model of toxic shock syndrome (TSS) by a TSS toxin-1-specific monoclonal antibody

An anti-TSST-1-specific monoclonal antibody (MAb 8-5-7) was tested for its protective capacity in a rabbit infection model to toxic shock syndrome (TSS). The challenge strain of Staphylococcus aureus (RN4710), which contained a plasmid encoding TSS toxin-1, was introduced into previously implanted chambers. Purified monoclonal antibody (1.25 mg of immunoglobulin G) administered parenterally 1 day before and 1 day after initiation of infection provided complete protection against the TSS-like syndrome and the mortality which occurred in unprotected rabbits.

Kinetics of phagocytosis and killing of E. coli by murine macrophages in presence of different serum preparations

In this study we evaluated the kinetics of phagocytosis and killing of E. coli by thioglycollate-elicited murine peritoneal macrophages and the role of specific antibodies and complement present in different serum preparations in modulating these processes. In our system phagocytosis of E. coli by macrophage monolayer was exponential for 180 min. The killing activity was high in the first 30-60 min and then virtually ceased. The least phagocytosis and killing occurred in presence of heat-inactivated fetal calf serum (HFCS). These activities were 2-fold increased in presence of normal mouse serum (NMS) or heat-inactivated newborn calf serum (HNCS) and were highly stimulated in presence of immune mouse serum (IMS). IMS without complement was less efficient in enhancing phagocytosis and killing by macrophages. However when IMS or HNCS were deprived of specific antibodies their activity was remarkably reduced. When macrophages containing phagocytized bacteria were reincubated with different sera, multiplication of intracellular E. coli occurred with HFCS, NMS or antibody-deprived IMS or HNCS. In contrast, a significant decrease in the survival of intracellular bacteria was seen in presence of IMS, HNCS or complement-deprived IMS. The results indicated that specific bacterial antibodies play a major role in the phagocytic process and in the activation of killing mechanisms. However optimal macrophage activity resulted from the presence of both specific antibodies and complement.

Neutralization of toxic shock syndrome toxin-1 by monoclonal antibodies in vitro and in vivo

Sixteen monoclonal antibodies (MAbs) directed against toxic shock syndrome toxin-1 (TSST-1) were generated by immunization of mice with purified TSST-1 and subsequent fusion of spleen cells with myeloma cells. Antibody-producing clones, identified by an enzyme-linked immunosorbent assay, were maintained as ascites tumors, and MAbs were purified by protein A chromatography. High-titered clones were further characterized and tested for the ability to neutralize several biological activities of TSST-1. The MAbs, which are of several immunoglobulin subtypes, reacted specifically with purified TSST-1 and TSST-1 present in Staphylococcus aureus culture supernatants. Three MAbs neutralized TSST-1-induced mitogenesis in a dose-dependent manner. Three of eight MAbs tested were able to neutralize induction by TSST-1 of interleukin-1 production by human monocytes. One neutralizing MAb, 8-5-7, was tested for the ability to protect rabbits from a constant infusion of TSST-1. Rabbits given the MAb had an attenuated clinical illness and were protected from the hypocalcemia, lipemia, and hepatic and renal insufficiency seen in control rabbits. Six of seven control rabbits died, compared with only one of seven rabbits treated with MAb 8-5-7. These experiments suggest that MAb 8-5-7 is directed against an antigenic determinant critical to the toxicity of TSST-1 and that the MAbs should be useful as probes in structure-function analyses of the TSST-1 molecule.

Synergistic induction of interleukin-1 by endotoxin and toxic shock syndrome toxin-1 using rat macrophages

We studied interleukin-1 (IL-1) secretion by rat peritoneal exudate macrophages stimulated with purified toxic shock syndrome toxin-1 (TSST-1). TSST-1 was observed to be a more potent inducer of IL-1 than was endotoxin. The induction of IL-1 secretion by TSST-1 was not blocked by polymyxin B but could be blocked by monoclonal antibodies directed against TSST-1. Synergistic induction of IL-1 was observed when the cells were stimulated with TSST-1 and endotoxin. The sequence of addition was found to be important for the synergistic response. Enhanced IL-1 production was observed only when macrophages were exposed to endotoxin before or simultaneously with TSST-1. Prior exposure of macrophages to TSST-1 had no enhancing effect on endotoxin-induced IL-1 secretion. We conclude that stimulation of the macrophage by endotoxin enhances the responsiveness of the cells to TSST-1 and may thereby play a role in the pathogenesis of toxic shock syndrome.

Thioglycollate elicited macrophages demonstrate enhanced virus replication and depressed bacterial killing

Thioglycollate elicited peritoneal macrophages of Balb/c mice exhibited minimal antibacterial activity against Listeria monocytogenes but were fully permissive for the replication of ectromelia virus. By comparison, resident and LPS elicited macrophages did not exhibited depressed antibacterial activity nor did they support viral replication. The thioglycollate effects were demonstrated in macrophages cultured in vitro and also in intact Balb/c mice. Mice given thioglycollate intraperitoneally and challenged by the same route suffered overwhelming virus and bacterial infections as a result of early local proliferation within peritoneal macrophages with subsequent spread to the liver. Balb/c mice challenged intravenously with similar doses of the virus of bacterial pathogen after administration of thioglycollate by the i.p. route did not succumb to either infection. Thus the ability of thioglycollate to compromise cellular host defenses against the infectious agents appears to be site specific; i.e. restricted to the peritoneal cavity where exudate macrophages and challenge inocula first come into contact.

Receptor-mediated entry of diphtheria toxin into monkey kidney (Vero) cells: electron microscopic evaluation

To express toxicity in living cells, diphtheria toxin (DT) must cross a membrane barrier and reach its target in the cytosol. Here we examine the entry of DT into the toxin-sensitive monkey kidney (Vero) cells. Using electron microscopy we directly demonstrated for the first time that DT is internalized by receptor-mediated endocytosis, i.e., via clathrin-coated pits, and enters the endosomal system. Methylamine, which is known to protect cells from DT, stopped the movement of toxin to coated areas of the cell membrane. In the presence of amine, prebound biotinyl-DT was internalized, but toxicity was inhibited. Biochemical evidence revealed that methylamine maintained toxin molecules at a site accessible to neutralization by antitoxin. The data suggest that DT entering Vero cells in the presence of methylamine is sequestered within the cell and does not express toxicity.

Visceral leishmaniasis in congenic mice of susceptible and resistant phenotypes: T-lymphocyte-mediated immunosuppression

This paper continues a comparative study (A. D. Nickol and P. F. Bonventre, Infect. Immun. 50:160-168, 1985) describing immune responses exhibited by congenic, Lshs mouse strains C57B1/10 (cure) and B10.D2 (noncure) during the course of disseminated leishmaniasis. We report that sublethal whole-body irradiation of B10.D2 mice before challenge with Leishmania donovani converted the noncuring mice to a curing phenotype. Splenic lymphocytes from L. donovani-infected B10.D2 mice failed to proliferate in response to parasite antigen stimulation in vitro. Splenic lymphocytes from irradiated, cured B10.D2 mice regained the capacity to respond to the parasite antigen stimulus. Transfer of T cells but not B cells from L. donovani-infected B10.D2 mice prevented the acquisition of immunity and recovery from infection in X-irradiated mice. In addition, a splenic T-cell population from L. donovani-infected B10.D2 mice suppressed the proliferation in vitro of parasite antigen-stimulated lymphocytes of irradiation-cured B10.D2 mice. Suppressor T cells were not demonstrable in the spleens of spontaneously cured C57B1/10 mice. Splenic lymphocytes from infected B10.D2 mice were deficient in the production of macrophage-activating factor (MAF) upon stimulation by L. donovani antigens in vitro. Deficient MAF production was specific for parasite antigen stimulation, because MAF production subsequent to concanavalin A stimulation of splenic lymphocytes from infected B10.D2 mice was not suppressed. The data suggest that a genetically based immunological defect in B10.D2 mice prevents the acquisition of effective cell-mediated immunity and subsequent elimination of L. donovani from tissue macrophages. The immunological deficit, not apparent in the curing C57B1/10, appears to be caused by the development of parasite antigen-specific suppressor T cells during the course of the disseminated leishmaniasis.

Visceral leishmaniasis in congenic mice of susceptible and resistant phenotypes: immunosuppression by adherent spleen cells

Visceral leishmaniasis is one of several parasitic diseases of humans characterized by immune suppression. A murine model of disseminated leishmaniasis utilizing inbred strains of specific genetic constitution was used to study the mechanisms of immunosuppression elicited during the course of infection. Resistant (Lshr) and susceptible (Lshs) strains of mice were challenged with amastigotes of Leishmania donovani and evaluated as to immune status at intervals between 2 and 40 weeks after challenge. The proliferative responses of splenic lymphocytes to T-cell mitogens, a B-cell mitogen, and parasite antigens were measured to evaluate the relative immune status of parasitized mice and noninfected control mice. Lymphocytes from resistant C3Heb/FeJ (C3H) mice responded normally to concanavalin A and phytohemagglutinin throughout the course of infection. Parasite antigen responses appeared 2 weeks after challenge of C3H mice and remained vigorous for periods up to 6 months. In contrast, immune suppression during infection was profound in both the curing (C57B1/10) and noncuring (B10.D2) phenotypes of Lshs congenic mice. Both Lshs strains developed severe infection as evidenced by high parasite burdens in the liver and spleen 4 to 5 weeks after challenge; splenic lymphocytes taken from these mice between 2 and 8 weeks became increasingly unresponsive to the T-cell mitogens as well as to parasite antigens. The noncuring B10.D2 mice which suffered chronic infection continued to be suppressed for as long as 40 weeks. C57B1/10 (curing) mice, in contrast, cleared infection between 12 and 16 weeks. After spontaneous recovery or elimination of parasites by antimonial drug therapy, the response of spleen cells to T-cell mitogens or parasite antigens were restored to normal. The spleen cells from the Lshs strains of mice obtained during the height of infection suppressed the proliferative responses of spleen cells from their uninfected counterparts upon cocultivation in vitro. Removal of adherent cells from the suppressive spleen cell populations restored normal mitogen responses. On the basis of adherence characteristics, phagocytosis, and morphology, the suppressor was identified as a macrophage population which appears to be responsible for a nonspecific immunosuppression of Lshs mice with significant parasite burdens of L. donovani.

Enhanced metabolism of Leishmania donovani amastigotes at acid pH: an adaptation for intracellular growth

Amastigotes (tissue forms) of Leishmania donovani isolated from infected hamster spleens carried out several physiological activities (respiration, catabolism of energy substrates, and incorporation of precursors into macromolecules) optimally at pH 4.0 to 5.5. All metabolic activities that were examined decreased sharply above the optimal pH. Promastigotes (culture forms), on the other hand, carried out the same metabolic activities optimally at or near neutral pH. This adaptation to an acid environment may account in part for the unusual ability of amastigotes to survive and multiply within the acidic environment of the phagolysosomes in vivo.

Immunosuppression associated with visceral leishmaniasis of hamsters

Immunosuppression was demonstrated during the course of Leishmania donovani infection of outbred and inbred hamsters. Proliferative responses of splenic lymphocytes to the mitogen concanavalin A (Con A) and to promastigote antigens were used as indicators of immune responsiveness. Although splenic lymphocyte proliferative responses to parasite antigens were demonstrable 3 weeks after challenge, antigen specific lymphocyte responses diminished as the infection progressed. Two types of immunosuppression were demonstrable. The first was a non-specific anergy of splenic lymphocytes to Con A stimulation. Thus, spleen cells from infected animals did not actively suppress the Con A responses of normal lymphocytes in mixed cultures A second immunosuppression mechanism, specific for leishmania antigens was mediated by a nylon wool non-adherent cell population. The suppressor, tentatively identified as a T cell population, inhibited the proliferation of parasite antigen sensitized responder lymphocytes in mixed culture. Elimination of the parasite burden by glucantime therapy restored responsiveness of lymphocytes to parasite antigens. Con A responses, however, remained suppressed 1 week after drug cure.

Synergistic effect of glucantime and a liposome-encapsulated muramyl dipeptide analog in therapy of experimental visceral leishmaniasis

A regimen of immunostimulation with 6-0-stearoyl-N-acetylmuramyl-L-alpha-aminobutyryl-D-isoglutamine, a lipophilic analog of muramyl dipeptide, combined with antimonial drug therapy was evaluated in the treatment of visceral leishmaniasis of mice and hamsters. The combined treatment was found to be more effective in the elimination of Leishmania donovani amastigotes from infected tissue macrophages than was either of the two treatments applied individually. In mice, it was found that immunostimulation of animals prophylactically, therapeutically, or both enhanced the effects of the antimonial drug (Glucantime) administered more than 1 week after a challenge of BALB/c and C57BL/6 mice. The superiority of the combined treatment of the parasite infection was demonstrable in both short-term (14 days) and long-term (40 to 45 days) infections of the two inbred strains of mice. The combined therapy was also effective in preventing the lethal course of leishmaniasis in hamsters which succumb to disseminated disease in the absence of therapeutic intervention. The efficacy of this dual approach to the therapy of disseminated leishmaniasis of experimental animals holds promise for similar application in the treatment of similarly afflicted human populations.

Enhancement of Glucantime therapy of murine Leishmania donovani infection by a synthetic immunopotentiating compound (CP-46,665-1)

The therapeutic efficacy of CP-46,665-1, a synthetic lipoidal amine with proven immunomodulatory and anti-tumor properties, in combination with chemotherapy was evaluated in L. donovani-infected C57Bl/6 mice. Immunostimulation and drug treatment resulted in a 10-fold lesser infection level than in untreated mice, while animals treated with Glucantime alone exhibited only a modest amelioration of the infection. We also studied the capacity of CP-elicited peritoneal macrophages of C57Bl/6 mice cultured alone or in combination with Glucantime and/or lymphokine to eliminate intracellular L. donovani amastigotes. When CP-elicited cells were incubated with Glucantime, they exhibited a significantly higher killing potential than did drug treated thioglycollate-elicited cells. CP-macrophages stimulated with lymphokine alone or in combination with antimonial drug, killed amastigotes more rapidly and efficiently than similarly treated thioglycollate-elicited macrophages. In vivo and in vitro results of this study show that a combined regimen of immunostimulation with CP and antimonial drug is more effective in treatment of L. donovani infection than either treatment alone.

Antibody responses to toxic-shock-syndrome (TSS) toxin by patients with TSS and by healthy staphylococcal carriers

Serum samples taken from women with toxic-shock syndrome (TSS) and from women without a history of TSS were examined for the presence of antibodies to toxic-shock-syndrome toxin (TST). Serum samples from 38 women with TSS and from 70 women with no history of TSS were analyzed by radioimmunoassay (RIA) and by an enzyme-linked immunoadsorbent assay (ELISA). Antitoxin titers obtained by the assays were highly correlated. Antibody levels in sera of women with TSS, or a history of TSS, were significantly lower than levels in sera of women with no prior evidence of TSS. The mean level of antitoxin titers in the total sample of acute, convalescent, and recovered TSS groups was significantly lower than that of the control groups, which consisted of 31 carriers of genital Staphylococcus aureus and a similar number of age- and race-matched noncarriers. Although a trend toward elevated antitoxin titers was apparent after recovery, no vigorous immunologic response to TST was noted. In contrast, the majority of healthy women demonstrated measurable antitoxin titers, a finding indicative of current or prior colonization with TST-producing strains of S. aureus. The data suggest that absence of antibodies to the TSS toxin may be a predisposing factor in the development of clinical disease.

Evidence for pseudomonas exotoxin A receptors on plasma membrane of toxin-sensitive lm fibroblasts

Pseudomonas exotoxin A enters mouse LM fibroblasts by receptor-mediated endocytosis and ultimately causes cell death. Here we present evidence for the existence of a specific receptor for the toxin. Toxin association with LM cells at 18 and 37 degrees C, but not at 4 degrees C, was highly specific. At 37 degrees C, the association increased with time, reaching a steady state by 5 h. Binding to paraformaldehyde-fixed cells at 37 degrees C was saturable (Kd = 5.4 nM), was reversible, and indicated ca. 100,000 binding sites per cell. It is believed that receptor-bound toxin is responsible for cell death. Once the kinetics of toxin entry were described, we examined the effect of reduced temperatures on the intracellular processing of toxin and thus its expression. Toxin-induced inhibition of protein synthesis was minimal at temperatures below 20 degrees C. This was seen even though at 20 degrees C sufficient toxin was internalized to kill cells, and toxin enzyme activity was maximal. Internalization of 125I-labeled toxin, but not of 125I-labeled horseradish peroxidase (marker of fluid-phase endocytosis), became rate limiting at 20 degrees C or below. These data suggest that reduced temperatures block a step in the receptor-mediated endocytic pathway essential for the expression of Pseudomonas toxin activity.

Rapid screening assay for toxic shock syndrome toxin production by Staphylococcus aureus

A rapid immunoblot assay (TST-blot) was developed and used to screen Staphylococcus aureus isolates for toxic shock syndrome toxin (TST) production. Growth from an 18-h stab inoculum of S. aureus on brain heart infusion agar was transferred directly to a nitrocellulose sheet. Nonspecific protein binding sites were blocked with bovine serum albumin, and the nitrocellulose sheet was incubated with affinity-purified antibody to TST, followed by incubation with horseradish peroxidase-conjugated protein A. Toxin was visualized by detection of the peroxidase-conjugated protein A-anti TST-TST complex with 4-chloro-1-napthol. The sensitivities and specificities of the TST-blot and Ouchterlony microslide immunodiffusion assay were compared by screening 141 S. aureus isolates for TST production. In both assays, 53 of 141 isolates produced detectable levels of TST, whereas 88 isolates produced no toxin. A 100% concordance was found between the two assays. The TST-blot yielded the same results in less than 24 h as those yielded by the 3-day immunodiffusion assay. Thus, this rapid method for detection of TST in multiple samples appears to be well suited for diagnostic and epidemiological studies. Furthermore, it would appear to be ideal for use in TST genetics research.

Enzymes of carbohydrate metabolism in Leishmania donovani amastigotes

A method for the isolation of Leishmania donovani amastigotes from infected hamster spleen and liver tissues is described. Over 85% of the isolated amastigotes were viable as judged by acridine orange-ethidium bromide staining and in vitro transformation to the promastigote form. A comprehensive survey of the enzymes of carbohydrate metabolism in L. donovani amastigotes and promastigotes was conducted. Amastigotes and promastigotes possess all of the enzymes of the Embden-Meyerhof pathway, hexose monophosphate shunt, and tricarboxylic acid cycle. Cell-free extracts of both forms demonstrate an active glutamate dehydrogenase, thus linking activity which permits entry of pyruvate into the tricarboxylic acid cycle. Both forms demonstrate an active glutamate dehydrogenase, thus linking amino acid metabolism with carbohydrate metabolism. Pyruvate carboxylase, the enzyme responsible for replenishment of C4 acids by heterotrophic CO2 fixation into pyruvate, was also demonstrable in the tissue and insect forms. In general, activities of promastigote enzymes are higher than the amastigote enzymes. Differences between the vertebrate (amastigote) and invertebrate (promastigote) forms in their potential to utilize carbohydrates as substrates would appear to be quantitative rather than qualitative.

Staphylococcal enterotoxin induced mitogenesis: toxin binding and cell-cell interactions

The binding characteristics of 125I-labelled staphylococcal enterotoxin A (125I-SEA), a T-cell mitogen, to murine lymphoid cell subpopulations were analyzed. Both T- and B-lymphocytes from murine spleens possess specific binding sites for SEA, as do T-lymphocytes from thymus. B-lymphocytes appear to have a greater capacity for binding of 125-SEA than do T-lymphocytes from either thymus or spleen. Enterotoxin did not specifically bind to thioglycollate-induced peritoneal exudate cells (PECs), used as a source of macrophages. Adherent PECs however, incorporated 125-ISEA by fluid phase endocytosis. When exposed to SEA and thoroughly washed, macrophages stimulate lymphocyte mitogenesis in spleen or thymus cell cultures not directly exposed to toxin. Maximum mitogenic stimulation took place only when both PECs and lymphocytes were exposed to SEA. The presence of splenic B-lymphocytes enhanced the mitogenic response of thymus derived T-cells to SEA. Thus, B-lymphocytes appear to contribute to SEA mitogenesis. These data suggest that mitogenic stimulation and possibly other immunological phenomena associated with SEA occur as a result of complex interactions between cellular components of the immune system.

Production of staphylococcal enterotoxin F and pyrogenic exotoxin C by Staphylococcus aureus isolates from toxic shock syndrome-associated sources

A total of 136 isolates of Staphylococcus aureus were tested for production of staphylococcal enterotoxin F (SEF) and pyrogenic exotoxin C (PEC), both of which have been identified as reliable indicators of toxic shock syndrome (TSS)-associated strains. SEF and PEC production by isolates from TSS-associated and other sources was tested independently in two laboratories, after which the two sets of data were compared. A 100% concordance between SEF and PEC production was obtained. The TSS toxin candidates were produced by 30 of 136 isolates, and in all instances SEF and PEC were made concurrently by the same strains; in no case was one toxin made and not the other. In the five groups of S. aureus tested, toxins were detected as follows: 23 of 25 (92%) acute TSS isolates, 2 of 48 (4.2%) genital non-TSS isolates, 2 of 16 (12.5%) recovered TSS isolates, 1 of 23 (4.3%) clinical nongenital isolates, and 2 of 24 (8.3%) enterotoxigenic food outbreak isolates. Comparison of purified SEF and purified PEC by immunological and biochemical criteria by immunodiffusion, isoelectric focusing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western blot analysis show that the toxins are immunologically identical and strongly suggest that the two nominal TSS toxins are in fact a single protein.

Efficacy of combined immunostimulation and chemotherapy in experimental visceral Leishmaniasis

A regimen of combined immunostimulation and chemotherapy for the elimination of Leishmania donovani amastigotes was evaluated. An in vitro experimental model utilized cultured peritoneal macrophages from C57B1/6 mice infected with L. donovani tissue forms. Partial or complete activation of macrophages as judged by killing of tumor cells significantly enhanced the efficacy of sodium antimony gluconate (Pentostam). The quantity of drug required for elimination of parasites from immunostimulated cells was considerably lower than that required to achieve comparable amastigote killing in thioglycolate-elicited macrophages. In contrast, amphotericin B cleared infected cells of amastigotes at comparable drug levels when tested with immunostimulated and unstimulated macrophages. Several drugs tested inhibited the conversion of amastigotes to promastigotes in vitro but were ineffective in killing of intracellular tissue forms. Allopurinol and difluoromethylornithine (DMFO) blocked amastigote conversion significantly. These drugs at high concentrations, however, exerted only minimal toxicity for amastigotes residing within macrophages. Efficacy of combined therapy was also demonstrated in vivo. Immunoenhancement of L. donovani-infected mice with Corynebacterium parvum vaccine combined with a regimen of sodium antimony gluconate was significantly more effective than was immunotherapy or drug therapy alone.

A role for oxygen-dependent mechanisms in killing of Leishmania donovani tissue forms by activated macrophages

Leishmania donovani, the causative agent of visceral leishmaniasis, infects macrophages (M phi ) of susceptible vertebrates. Immunologically activated M phi are leishmanicidal, but the mechanisms involved in the killing process are not well defined. We sought to investigate the role of reactive oxygen intermediates in the killing of L. donovani. Both the free-swimming promastigote and the intracellular amastigote forms were found to be susceptible to killing in vitro by hydrogen peroxide and other oxygen intermediates. Upon phagocytosis by mouse peritoneal M phi, promastigotes elicited a significantly stronger respiratory burst compared with amastigotes as measured by release of superoxide anion. Although amastigotes do not elicit a strong burst of M phi oxidative metabolism during the initial phagocytic event, immunologically activated M phi that acquired leishmanicidal capacity could be triggered to release substantial amounts of H2O2. Hence, the development of leishmanicidal capacity was correlated temporally with enhanced H2O2 generation by the M phi. In contrast, M phi that lost their ability to release significant amounts of H2O2 after several days in culture were unable to eliminate their parasite burden. Catalase markedly inhibited the elimination of amastigotes by lymphokine-stimulated M phi. In toto, the results implicate reactive oxygen intermediates in killing of the tissue form of L. donovani by its host cell, the mononuclear phagocyte.

A role for oxygen-dependent mechanisms in killing of Leishmania donovani tissue forms by activated macrophages

Leishmania donovani, the causative agent of visceral leishmaniasis, infects macrophages (M phi ) of susceptible vertebrates. Immunologically activated M phi are leishmanicidal, but the mechanisms involved in the killing process are not well defined. We sought to investigate the role of reactive oxygen intermediates in the killing of L. donovani. Both the free-swimming promastigote and the intracellular amastigote forms were found to be susceptible to killing in vitro by hydrogen peroxide and other oxygen intermediates. Upon phagocytosis by mouse peritoneal M phi, promastigotes elicited a significantly stronger respiratory burst compared with amastigotes as measured by release of superoxide anion. Although amastigotes do not elicit a strong burst of M phi oxidative metabolism during the initial phagocytic event, immunologically activated M phi that acquired leishmanicidal capacity could be triggered to release substantial amounts of H2O2. Hence, the development of leishmanicidal capacity was correlated temporally with enhanced H2O2 generation by the M phi. In contrast, M phi that lost their ability to release significant amounts of H2O2 after several days in culture were unable to eliminate their parasite burden. Catalase markedly inhibited the elimination of amastigotes by lymphokine-stimulated M phi. In toto, the results implicate reactive oxygen intermediates in killing of the tissue form of L. donovani by its host cell, the mononuclear phagocyte.

Development of protective immunity against bacterial and viral infections in tumor-bearing mice coincident with suppression of tumor immunity

This report addresses the question whether Meth A (methylcholanthrene-induced fibrosarcoma) tumor bearing Balb/c mice are able to develop specific antimicrobial immunity. Although specific suppressor T lymphocytes appeared during tumor growth which prevented expression of antitumor immunity, the development of protective immunity to L monocytogenes, S. pneumoniae or ectromelia virus infections was unimpaired. The Meth A tumor produced a soluble immunosuppressive factor which inhibited lymphocyte and macrophage functions in vitro. Tumor growth failed to inhibit the formation of immunoglobulin essential to antipneumococcal immunity, or the development of a specific acquired cellular resistance of primary importance in immunity to listeria and ectromelia virus infections. That tumor growth did not interfere with the development of cell mediated immunity was demonstrated by the effective transfer of antilisteria immunity by immune spleen from tumor-bearing mice.

The epidemiology of genital colonization with Staphylococcus aureus

The prevalence of genital colonization with Staphylococcus aureus, including strains that have been associated with toxic shock syndrome, was studied in 600 women. Nine percent of these women were colonized with S. aureus, 5% of whom had positive vaginal cultures, and 1% were colonized with toxin-producing strains. Black women were colonized with S. aureus, including toxin-producing strains, as frequently or more frequently than white women. The highest colonization rates occurred in postpartum women. Trends toward increasing colonization occurred in relation to decreasing age and socioeconomic status. There were no statistically significant relationships between genital colonization with S. aureus and the use of tampons, oral contraceptives, or a variety of other personal habits and health problems. Genital cultures taken in consecutive menstrual cycles indicated that 35% of women with S. aureus were persistent carriers, and the rest either intermittent or transient carriers. Toxin-producing S. aureus was also identified in family members of women carrying the same organism. This report defines the prevalence of genital colonization in a large population of women, characterizes the women with S. aureus, and describes epidemiologic features of genital carriage.