Proliferative response and cytokine production of bovine peripheral blood mononuclear cells induced by the superantigens staphylococcal enterotoxins and toxic shock syndrome toxin-1

Photoactivated Gallium Porphyrin Reduces Staphylococcus aureus Colonization on the Skin and Suppresses Its Ability to Produce Enterotoxin C and TSST-1

Staphylococcus aureus is a key pathogen in atopic dermatitis (AD) pathogenicity. Over half of AD patients are carriers of S. aureus. Clinical isolates derived from AD patients produce various staphylococcal enterotoxins, such as staphylococcal enterotoxin C or toxic shock syndrome toxin. The production of these virulence factors is correlated with more severe AD. In this study, we propose cationic heme-mimetic gallium porphyrin (Ga3+CHP), a novel gallium metalloporphyrin, as an anti-staphylococcal agent that functions through dual mechanisms: a light-dependent mechanism (antimicrobial photodynamic inactivation, aPDI) and a light-independent mechanism (suppressing iron metabolism). Ga3+CHP has two additive quaternary ammonium groups that increase its water solubility. Furthermore, Ga3+CHP is an efficient generator of singlet oxygen and can be recognized by heme-target systems such as Isd, which improves the intracellular accumulation of this compound. Ga3+CHP activated with green light effectively reduced the survival of clinical S. aureus isolates derived from AD patients (>5 log10 CFU/mL) and affected their enterotoxin gene expression. Additionally, there was a decrease in the biological functionality of studied toxins regarding their superantigenicity. In aPDI conditions, there was no pronounced toxicity in HaCaT keratinocytes with both normal and suppressed filaggrin gene expression, which occurs in ∼50% of AD patients. Additionally, no mutagenic activity was observed. Green light-activated gallium metalloporphyrins may be a promising chemotherapeutic to reduce S. aureus colonization on the skin of AD patients.

Relationship between virulence factors and antimicrobial resistance in Staphylococcus aureus from bovine mastitis

OBJECTIVES

This review summarizes the literature on the role of virulence and antimicrobial resistance genes of Staphylococcus aureus in bovine mastitis, focusing on the association between these characteristics and their implications for public and animal health.

CONCLUSIONS

There is the possibility of antimicrobial resistance gene exchange among different bacteria, which is of serious concern in livestock husbandry, as well as in the treatment of human staphylococcal infections.

Staphylococcal Immune Evasion Proteins: Structure, Function, and Host Adaptation

Staphylococcus aureus is a successful human and animal pathogen. Its pathogenicity is linked to its ability to secrete a large amount of virulence factors. These secreted proteins interfere with many critical components of the immune system, both innate and adaptive, and hamper proper immune functioning. In recent years, numerous studies have been conducted in order to understand the molecular mechanism underlying the interaction of evasion molecules with the host immune system. Structural studies have fundamentally contributed to our understanding of the mechanisms of action of the individual factors. Furthermore, such studies revealed one of the most striking characteristics of the secreted immune evasion molecules: their conserved structure. Despite high-sequence variability, most immune evasion molecules belong to a small number of structural categories. Another remarkable characteristic is that S. aureus carries most of these virulence factors on mobile genetic elements (MGE) or ex-MGE in its accessory genome. Coevolution of pathogen and host has resulted in immune evasion molecules with a highly host-specific function and prevalence. In this review, we explore how these shared structures and genomic locations relate to function and host specificity. This is discussed in the context of therapeutic options for these immune evasion molecules in infectious as well as in inflammatory diseases.

The Immunology of Mammary Gland of Dairy Ruminants between Healthy and Inflammatory Conditions

The health of dairy animals, particularly the milk-producing mammary glands, is essential to the dairy industry because of the crucial hygienic and economic aspects of ensuring production of high quality milk. Due to its high prevalence, mastitis is considered the most important threat to dairy industry, due to its impacts on animal health and milk production and thus on economic benefits. The MG is protected by several defence mechanisms that prevent microbial penetration and surveillance. However, several factors can attenuate the host immune response (IR), and the possession of various virulence and resistance factors by different mastitis-causing microorganisms greatly limits immune defences and promotes establishment of intramammary infections (IMIs). A comprehensive understanding of MG immunity in both healthy and inflammatory conditions will be an important key to understand the nature of IMIs caused by specific pathogens and greatly contributes to the development of effective control methods and appropriate detection techniques. Consequently, this review aims to provide a detailed overview of antimicrobial defences in the MG under healthy and inflammatory conditions. In this sense, we will focus on pathogen-dependent variations in IRs mounted by the host during IMI and discuss the potential ramifications of these variations.

Superantigen gene profiles, genetic relatedness and biological activity of exosecretions of Staphylococcus aureus isolates obtained from milk of cows with clinical mastitis

This study evaluated the superantigen gene profiles, genetic relatedness and biological activity of exosecretions of 50 Staphylococcus aureus isolates obtained from milk of cows with clinical mastitis. Genomic relatedness of S. aureus was determined by pulsed field gel electrophoresis analysis of macro-restricted chromosomes. The presence of genes encoding superantigens was confirmed by multiplex PCR. To study the biological activity of S. aureus exosecretions, the supernatants from bacterial liquid cultures were classified into three groups: those with leukotoxin‐like properties, those with superantigen‐like properties and those with no particular activity on leukocytes cultured in vitro. It was shown that all analyzed bacterial isolates belonged to the same clonal type and harbored the same combination of superantigen genes, namely sed, selj and ser. However, 22% of all isolates produced factors with superantigen‐like and 48% of them with leukotoxin‐like activities. Finally, although there were no detectable genetic differences between the analyzed bacterial isolates, the virulence factors secreted by them differed considerably.

Influence of S. aureus exosecretions on cytokine profile in bovine leukocyte cultures in vitro

The aim of the research was to evaluate the in vitro effect of Staphylococcus aureus exosecretions on the expression of genes encoding IL-2 and IL-12 and secretion of IFN-γ and TNF-α, in bovine leukocyte cultures in vitro. The research was based on 30 S. aureus isolates collected from milk samples from cows with clinical mastitis. Supernatants prepared from the bacterial liquid cultures, which were used to treat leukocytes, were divided into three groups: one with superantigen-like properties, one with leukotoxic-like properties and the one without superantigen or leukotoxic-like properties. The MNC, PMN and MIX (consisted of MNC and PMN leukocytes) cultures were grown and treated with the supernatants. The work shows that the effect on the cytokine gene expression and cytokine secretion caused by S. aureus exosecretions is mainly due to the presence of virulence factors connected with superantigen-like activity and less with leukotoxic-like activity whereas exosecretions of other activity are not or only slightly involved in this process.

Tumor necrosis factor alpha increases P-glycoprotein expression in a BME-UV in vitro model of mammary epithelial cells

P-glycoprotein is an efflux pump belonging to the ATP-binding cassette super-family that influences the bioavailability and disposition of many drugs. Mammary epithelial cells express various drug transporters including P-glycoprotein, albeit at low level during lactation. During inflammatory reactions, which can be associated with changes in epithelial barrier functions, pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) are elevated in milk and serum. In this study, the role of TNF-α in the regulation of P-glycoprotein was determined in cultured BME-UV cells, an immortalized bovine mammary epithelial cell line. The protein production of P-glycoprotein and mRNA expression of bABCB1, the gene encoding P-glycoprotein, were increased after 24 h of TNF-α exposure. The highest observed effects for TNF-α on the regulation of P-glycoprotein was after 72 h of exposure. Protein and mRNA expression also increased significantly after 120 h of TNF-α exposure, but was lower than the level observed in the cells exposed to TNF-α for 72 h. The apical to basolateral flux of digoxin, a P-glycoprotein substrate, was decreased in the TNF-α-exposed epithelium. This effect was reversed when verapamil or ketoconazole, compounds known to interact with P-glycoprotein, were added together with digoxin into the donor compartment. Probenecid, a compound known to interact with organic anion transporters, but not P-glycoprotein, did not increase the flux of digoxin. This model has important implications for understanding the barrier function of the mammary epithelium and provides insight into the role of P-glycoprotein in the accumulation and/or removal of xenobiotics from milk and/or plasma.

Long-term staphylococcal enterotoxin C1 exposure induces soluble factor-mediated immunosuppression by bovine CD4+ and CD8+ T cells

Regulatory T cells (T(regs)) help control the development and maintenance of protective immunity and can lead to aberrant immune responses to some pathogens. Several lines of evidence suggest that T(regs) are induced by exposure to superantigens (SAgs) in vitro or in vivo. In this study, bovine peripheral blood mononuclear cells (PBMC) were exposed in vitro to a relatively low dose (5 ng/ml) of staphylococcal enterotoxin C1 (SEC1) for up to 10 days. Upon stimulation, CD4+ and CD8+ T cells initially proliferated at similar rates. Subsequently, from days 6 through 10, most CD4+ and CD8+ T cells proliferated regardless of Vbeta specificity, but the proliferation of CD8+ T cells occurred more vigorously. The transcription of CD25 and CD152 genes increased, whereas that of interleukin-2 (IL-2) decreased. gammadelta T cells appeared to be unresponsive. An increase in the transcription of IL-10 and transforming growth factor beta (TGF-beta) genes in SEC1-stimulated cultures was attributed to the CD4+ CD25+ T-cell subpopulation. The expression of Foxp3 mRNA also increased and was accompanied by the upregulation of CD152 and the downregulation of IL-2 transcription, suggesting that cells in this subpopulation are T(regs). Functionally, SEC1-stimulated CD4+ T cells suppressed the proliferation of naive PBMC in response to heat-killed-fixed Staphylococcus aureus. The suppression was partially mediated by IL-10 and TGF-beta, another characteristic of certain types of T(regs.) The CD8+ T-cell population also suppressed naive PBMC through another mechanism not mediated by IL-10 or TGF-beta. These results provide further insight into the potential mechanisms by which SAgs could contribute to evasion of the immune response, affecting the outcome of infection or colonization.

Inflammatory effect of cleaved bovine lactoferrin by elastase on staphylococcal mastitis

Elastase activity and concanavalin A (Con A) low affinity bovine lactoferrin (bLf) molecule were detected in mammary gland secretions (MGSs) from mammary glands (MGs) with clinical staphylococcal mastitis. Changes in clinical symptoms correlated with increases in both elastase activity and the concentration of Con A low-affinity Lf in MGSs from mastitic MGs. Bovine Lf treated with elastase (elastase-Lf) showed various small bLf molecules and the same image on Con A two-dimensional immunoelectrophoresis as low Con A affinity bLf in MGSs. We confirmed the presence of four common bLf peptides for the elastase-bLf and low Con A affinity bLf molecules in mastitic MGSs, and synthesized four peptides. Strong mRNA expression of interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) was induced in bovine mammary epithelial cells on stimulation with low Con A affinity bLf, elastase-bLf, and GQRDLLFKDSAL, a synthesis bLf peptide based on nuclear factor kappa B (NFkappaB) activation. These results suggest that bLf was cleaved by elastase, and that this cleavage changed the physical function of Lf. Our results indicate that elastase induced production of low Con A affinity bLf, including the bLf peptide GQRDLLFKDSAL, and had an inflammatory effect on staphylococcal mastitis.

Prevalence of Enterotoxin and Toxic Shock Syndrome Toxin Genes inStaphylococcus aureusIsolated from Milk of Cows with Mastitis

Staphylococcus aureus isolated from milk of cows with mastitis were evaluated for the prevalence of 16 enterotoxin genes (sea-see and seg-seq) and toxic shock syndrome toxin gene (tsst-1). Of 78 S. aureus examined, 73 (93.6%) were positive for one or more enterotoxin genes and these were divided into 36 groups by the presence of different enterotoxin genes. Enterotoxin genes including sen (84.6%), sem (71.8%), sei (60.3%) and sed (52.6%) were found frequently, while seg (24.4%), seq (16.7%), seo (12.8%), and seb (1.3%) were found at lower frequencies. Toxic shock syndrome toxin (tsst-1) gene was detected in 20 (25.6%) isolates and was always found in combination with other enterotoxin genes. The majority (88.5%) harbored more than one enterotoxin gene in different combinations. Eight S. aureus isolates (10.3%) were positive for sed, sei, sem, and sen; six (7.7%) possessed sed, seg, sei, sem, sen, and tsst-1; five (6.4%) had sei, sem, and sen; and four (5.1%) had sei, and sen. One isolate was positive for seb along with other SE genes including sed, seh, sem, sen, seq, and tsst-1. None of the isolates carried other enterotoxin genes (sea, sec, see, sej, sek, sel, and sep). PFGE profiles revealed 15 distinct pulsotypes among the 78 S. aureus isolates evaluated. PFGE and enterotoxin gene profiles did not match with each other because a single pulsotype carried different combinations of enterotoxin genes. The majority of S. aureus isolated from milk of mastitic cows carried newly described SE genes sem, sen and sei along with classical SE genes, sed and tsst-1. This is the first report describing the high prevalence of newly described enterotoxin genes, sem and sen in S. aureus from bovine mastitis. The high prevalence of enterotoxin genes and tsst-1 in S. aureus may be important as it is relevant to udder pathogenicity and food hygiene.

Staphylococcus aureus enterotoxin D is secreted in milk and stimulates specific antibody responses in cows in the course of experimental intramammary infection

An enterotoxin D (SED)-producing strain of Staphylococcus aureus was used to infect one mammary gland of each of 17 lactating dairy cows. All glands became infected and shed bacteria over a sampling period of 3 weeks. Serum and milk antibodies specific for SED were monitored by an enzyme-linked immunosorbent assay for 12 weeks. Elevated anti-SED antibodies were detected in all cows after infection, and immunoglobulin of the G2 subclass comprised most of the specific serum response. SED was detected in mastitic milk samples from two cows at levels of 5 to 10 ng/ml. An in vitro lymphocyte proliferation assay showed that SED at levels below 10 pg/ml induced proliferation of bovine lymphocytes and that sheep antiserum specific for SED neutralized this proliferative response. Sera obtained from the cows pre- and postinfection inhibited lymphocyte proliferation at SED concentrations of 10 and 50 ng/ml, respectively. The addition of SED to whole blood or to isolated neutrophils had no significant effect on neutrophil function in vitro. The results show that SED is secreted during mammary gland infection, is mitogenic for bovine lymphocytes, and stimulates the production of specific antibodies.

Age-dependent differences in cytokine and antibody responses after experimental RSV infection in a bovine model

Respiratory syncytial virus (RSV) causes severe respiratory disease in both infants and calves. As in humans, bovine RSV (BRSV) infections are most severe in the first 6 months of life. In this study, experimental infection with BRSV was performed in calves aged 1-5, 9-16 or 32-37 weeks. Compared to younger animals, older calves showed significantly less fever and lower TNFalpha levels and less virus-specific IFNgamma release. In addition, blood from older animals had more mononuclear cells, more B cells and stronger BRSV-specific IgA and neutralising antibody responses to infection. A strong "inflammatory" but weak humoral antiviral response in very young animals suggests that enhanced inflammation contributes to disease during RSV infection during the early postnatal period.

Tumor necrosis factor-alpha up-regulation in spontaneously proliferating cells derived from bovine leukemia virus-infected cattle

We previously reported that tumor necrosis factor alpha (TNF-alpha) was one of the cytokines that contributed to the leukemogenesis caused by bovine leukemia virus (BLV). To determine if the spontaneous cell proliferation observed in the late disease stages, such as persistent lymphocytosis and lymphosarcoma, correlated with the expression level of TNF-alpha, we analyzed the mRNA expression levels for TNF-alpha in spontaneously proliferating PBMCs derived from BLV-infected cattle. The mean mRNA expression level for TNF-alpha was higher in the spontaneously proliferating PBMCs derived from BLV-infected cattle than in non-spontaneously proliferating PBMCs from normal cattle. The TNF-alpha protein level in the PBMCs was determined by flow cytometric analysis, and it was noted that most of the cells expressing membrane-bound TNF-alpha in the spontaneously proliferating cells were CD5+ or sIgM+-cells. Additionally, in order to determine if this spontaneous proliferation can be blocked by anti-bovine TNF-alpha MAb, the spontaneously proliferating PBMCs from a BLV-infected cattle were cultured in the presence of the MAb. The addition of this MAb at the beginning of the 72 h-cultivation clearly inhibited spontaneous proliferation of cells in a dose-dependent manner, indicating the direct involvement of TNF-alpha in the spontaneous proliferation of PBMCs during the late disease stage. These data suggest that an aberrant expression of TNF-alpha might contribute to the progression of bovine leukosis in animals which develop persistent lymphocytosis of B-cells or B-cell lymphosarcoma.

Pattern of enterotoxin genes seg, seh, sei and sej positive Staphylococcus aureus isolated from bovine mastitis

PCR detection of the genes encoding the newly described staphylococcal enterotoxins (SE) SEG, SEH, SEI and SEJ was carried out for 104 randomly selected Staphylococcus aureus field strains isolated from cases of bovine mastitis. Sixty-one (58.7%) isolates were positive for one or more of these novel enterotoxin genes. Thirty-six field strains were classified as carrier of seg, 22 of sei gene and 23 were positive for sej gene. None of the 104 investigated ruminant S. aureus strains carried the seh gene. Thirty-seven of these S. aureus strains showed a combination of genes encoding enterotoxin types SEA to SEE or toxic shock syndrome toxin 1 (TSST 1). Thirteen cultures harboured only one, 28 two, 12 three and 8 four enterotoxin genes. Among the 61 S. aureus field strains 14 (23.0%) were positive for the genes encoding SEJ and SED and 10 (16.4%) isolates for those encoding SEG and SEI. Isolates harbouring the sed/sej genes were further characterized by macrorestriction analysis and pulsed-field-gelelectrophoresis (Pfge). Macrorestriction analysis revealed six patterns. Nine of these14 S. aureus isolates (64.3%) exhibited two patterns with a high degree of relationship (>80%).

The cytokines of bovine mammary gland: prospects for diagnosis and therapy

The lack of efficacy of conventional strategies for the maintenance of healthy udders in domestic cattle has prompted studies on the use of cytokines for this purpose. The adjuvant use of recombinant bovine cytokines, such as IL-2, IFN-gamma and TNF-alpha, in normal mammary gland, mobilizes innate and acquired immunity. However, stimulated immunity does not prevent or eradicate infection, particularly in the case of Staphylococcus aureus mastitis. Cytokines do, however, improve the bactericidal efficiency of certain antibiotics. The subtle and sensitive changes in the cytokine network of normal and mastitic bovine mammary gland may encourage the use of cytokines in the diagnosis and prognosis of udder health. Numerous studies support this hypothesis, and detection and monitoring of cytokines could become an important alternative management for udder health. The use of cytokines in the immunotherapy, diagnosis and prognosis of mastitis will grow with knowledge of the cytokine network in bovine mammary glands and the development of efficient cytokine diagnostic techniques.

Inflammatory responses of bovine polymorphonuclear neutrophils induced by staphylococcal enterotoxin C via stimulation of mononuclear cells

To elucidate the pathological roles of staphylococcal enterotoxin C (SEC) in bovine staphylococcal mastitis, a histopathological analysis of SEC-inoculated mammary glands was performed. SEC-inoculated mammary glands exhibited interstitial inflammation, and the leukocytes that migrated into the gland were predominantly polymorphonuclear neutrophils (PMN). In the gland cistern tissues dissected from SEC-inoculated mammary glands, epithelial cellular degeneration was observed. We also investigated the physiological effects of SEC on PMN in vitro. PMN migration was induced by culture supernatant of SEC-stimulated peripheral blood mononuclear cells (S-PBMC sup) but not by that of nonstimulated PBMC (N-PBMC sup). The concentration of interleukin-8 was significantly (P < 0.05) higher in S-PBMC sup than N-PBMC sup, and a significantly (P < 0.05) higher mRNA expression of growth-regulated oncogenes was detected in SEC-stimulated PBMC than in nonstimulated PBMC. Milk PMN collected from SEC-inoculated mammary glands produced more than 2 times the amount of superoxide at 1 day postinoculation (dpi) than at 0 dpi in the presence of phorbol 12-myristate 13-acetate (PMA). PMN cultured with S-PBMC sup for 24 h also produced significantly (P < 0.05) larger amounts of superoxide than those cultured with N-PBMC sup in the presence of PMA. Moreover, S-PBMC sup induced the long-time survival of PMN. These results indicate that SEC induces the activation of PMN via the stimulation of mononuclear cells.

Occurrence and clonal relatedness of sec/tst-gene positive Staphylococcus aureus isolates of quartermilk samples of cows suffering from mastitis

AIMS

To investigate the prevalence of sec/tst-gene positive Staphylococcus aureus in bovine mastitis and to get information about the clonal relatedness of these clinical isolates.

METHODS AND RESULTS

A total of 533 Staph. aureus strains isolated from bovine mastitic quartermilk samples at 493 randomized dairy farms in Hessia, Germany, from January 1997 until June 1998 were examined for enterotoxin C (sec) gene and toxic shock syndrome toxin (tst) gene by multiplex polymerase chain reaction. Fifty-three (9.3%) of the strains were sec/tst-gene positive. Phenotypic TSST-1 production was found in all positive strains by reversed passive latex agglutination test. With DNA macrorestriction analysis, sec/tst-gene positive strains were divided into five different macrorestriction types. Type I (10 isolates) and III (40 isolates) were found to be the predominant types in terms of frequency of isolation in the investigated area. These DNA macrorestriction types differed in only two bands in the 500 and 270 bp region.

CONCLUSIONS

Closely related Staph. aureus strains seem to be responsible for an unusual large proportion of bovine mastitis cases in geographically widely distinct locations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is one of the first reports about the relatedness of sec/tst-gene positive Staph. aureus clinical isolates from bovine mastitis.

Induction of nitric oxide production mediated by tumor necrosis factor alpha on staphylococcal enterotoxin C-stimulated bovine mammary gland cells

Mammary gland (MG) secretions (MGS) derived from secretory cows infected with coagulase-negative staphylococci (CoNS) showed somatic cell counts and lactoferrin similar to levels found in the MGS of secretory cows infected with Staphylococcus aureus. However, nitrite and nitrate (NOx) and staphylococcal enterotoxin C (SEC) were found in MGS infected with S. aureus at much higher levels than in cows infected with CoNS. These results suggested that NOx could be intimately correlated with the production of SEC in secretory cows infected with S. aureus. Therefore, we examined the production of NOx and the expression of proinflammatory cytokines and microsomal cytochrome P450 (CYP450) after injection of SEC into the MGS of secretory cows. We were able to detect NOx and the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) on MG cells of SEC-injected MGS. It was also found that CYP450 in the MG cells from SEC-injected MGS was down-regulated by approximately one-third in comparison with the cells from phosphate-buffered saline-injected MGS. This in vitro system also showed that NOx could be induced in the culture of bovine macrophage-lined cells (FBM-17) with the supernatants of SEC-stimulated bovine peripheral blood lymphocytes (BoPBLs) but not in the culture of peripheral mononuclear cells with SEC-stimulated BoPBLs. The expression of the mRNA for both inducible nitric oxide synthase and TNF-alpha in FBM-17 was enhanced by culturing with the supernatant of SEC-stimulated BoPBLs, although CYP450 was down-regulated. These results indicate that the down-regulation of CYP450 was caused by the production of TNF-alpha in SEC-stimulating MG cells containing macrophages and via NOx production. Therefore, we suggest that NOx released from activated MG cells via the superantigenic activity of SEC caused oxidative damage to the MG in S. aureus-induced mastitis.

Concentrations and specific antibodies to staphylococcal enterotoxin-C and toxic shock syndrome toxin-1 in bovine mammary gland secretions, and inflammatory response to the intramammary inoculation of these toxins

To investigate the pathological role of staphylococcal enterotoxins (SEs) and toxic shock syndrome toxin-1 (TSST-1) in bovine mastitis, the production of SEs and TSST-1 was investigated in staphylococci isolated from 120 mammary gland secretions (MGS, 51 from no clinical sign-mammary glands and 69 from staphylococcal mastitic-mammary glands) collected from dairy farms where staphylococcal mastitis frequently occurred in Miyagi and Yamagata prefectures from 1997 to 1998. Concentrations of these toxins and specific antibody titers in each MGS were also measured. Furthermore, SEC and TSST-1 were inoculated into lactating mammary glands and inflammatory responses were analyzed. A high percentage of staphylococci including Staphylococcus aureus and coagulase-negative staphylococci isolated from both no clinical sign- and mastitic-MGS produced both SEC and/or TSST-1. The concentration of SEC increased with the severity of the mastitis, and was significantly higher (P<0.05) in acute mastitic-than in no clinical signs-MGS. Titers of specific antibodies to TSST-1 in MGS were significantly higher (P<0.05) than those to SEC, regardless of whether or not the cows were lactating or mastitic. Specific antibodies purified from MGS neutralized each toxin in vitro. A significant increase (P < 0.05) in somatic cell counts was induced by the intramammary inoculation of SEC but not TSST-1. These findings indicated that SEC rather than TSST-1 plays an important role in the pathology of staphylococcal bovine mastitis. The inflammatory activity of TSST-1 was probably neutralized by specific antibodies in MGS.

The cytokine markers in Staphylococcus aureus mastitis of bovine mammary gland

TaqMan real time PCR was used to study the transcriptional activity of the bovine IL-2, IL-6, IL-12p40, IFN-gamma, TNF-alpha and granulocyte-monocyte colony stimulating factor of whole milk cells in bovine mammary gland experimentally infected with Staphylococcus aureus. Cytokine transcriptional activity was monitored at 7, 24 and 32 h Post-infection (Pi). IL-12 and TNF-alpha levels were significantly elevated at 24 h Pi followed by sharp decrease at 32 h pi. IL-2 level was decreased at 32 h pi. IL-12 and IFN-gamma showed a significant interaction at 24 h pi. The significant elevations of the IL-12 and TNF-alpha transcriptional level most likely indicate their important role in regulation of the immune responses of bovine mammary gland in S. aureus infection. Depression of IL-2 could reflect the suppressive nature of the S. aureus mastitis.

Frequency of superantigen-producing Staphylococcus intermedius isolates from canine pyoderma and proliferation-inducing potential of superantigens in dogs

This preliminary study investigated the potential role of staphylococcal superantigens in the pathogenesis of canine pyoderma. The staphylococcal enterotoxins A (SEA), SEB, SEC and SED, and the toxic shock syndrome toxin-1 (TSST-1) were assayed in isolates from skins of dogs with pyoderma. Culture supernatants from 25 of 96 isolates were positive for multiple superantigens, with SEA and SEC being the most frequently detected. In in vitro stimulation of canine peripheral blood mononuclear cells and quantitative flow cytometry revealed that low concentrations of SEA and SEB were potent stimulators of blastogenesis of T cells.

Costimulatory molecule requirement for bovine WC1+gammadelta T cells' proliferative response to bacterial superantigens

We have previously shown that the proliferation of freshly isolated bovine WC1+gammadelta T cells to superantigens (SAgs) including staphylococcal enterotoxin A (SEA), and staphylococcal enterotoxin B (SEB) or toxic shock syndrome type-1 (TSST-1) required the presence of antigen-presenting cells (APC) and the addition of exogenous interleukin (IL)-2. The costimulatory activity provided by molecules expressed on professional APC for the proliferation of gammadelta T cells has not been addressed hitherto. In the present study, we investigated the ability of two selected APC populations, the dendritic cells (DCs) highly expressing CD80 and CD86 molecules (CD80highCD86high) and the monocytes expressing the same molecules at a rather low level (CD80lowCD86low), to stimulate the proliferation of purified bovine WC1+gammadelta T cells to SAgs. DCs were more efficient than monocytes in inducing gammadelta T-cell proliferation, and this response was dependent on exogenous IL-2 in both presentation modes. Stimulating gammadelta T cells with gradual doses of SAgs or concanavalin A (ConA) resulted in similar dose-dependent reaction profiles suggesting a minimal role of the major histocompatibility complex (MHC). However, significant proliferation was already obtained with the starting doses in the presence of DC compared with monocytes, and higher proliferation was reached with DC at optimal doses. Finally, the addition of monoclonal antibody (MoAb) anti-CD86 markedly inhibited SAgs- and ConA-mediated proliferation, whereas MoAb anti-CD80 had no effect. The combination of both anti-CD80 and anti-CD86, however, suppressed this response. These results suggest that bovine gammadelta T-cell proliferation response requires indubitably CD86 costimulation. The role of CD80 molecule seems less clear.

Characterization of leukocytotoxic and superantigen-like factors produced by Staphylococcus aureus isolates from milk of cows with mastitis

Staphylococcus aureus is a major pathogen for cattle, causing various forms of subclinical and clinical mastitis. Two groups of virulence factors (leukotoxins and superantigens) are supposed to play an important role in the initiation and/or the exacerbation of this disease. In order to detect all known and putative members of leukotoxins and SAgs (superantigens), we tested secreted factors of different S. aureus isolates in flow cytometry-based assays. Isolates were sampled from 68 cows of different farms and cultured for 24h in vitro. Supernatants were then coincubated with purified polymorphonuclear granulocytes (PMN) or combinations of blood mononuclear cells (MNC) and PMN. Viable PMN and MNC were determined by quantitative flow cytometry. In addition, we recorded the proliferation-inducing potential of isolate supernatants for bovine MNC. Based on these criteria, the supernatants of S. aureus isolates fell in three groups. The first group (n=32), termed LT-SNs (leukotoxin-containing supernatants), killed purified granulocytes (neutrophils and eosinophils) in vitro. The second group of supernatants (n=20), termed SAg-SN (superantigen-containing supernatants), induced activation and proliferation of mononuclear cells (MNC) and, only in the presence of MNC, resulted in a selective depletion of neutrophils after 24h in vitro. The third group of supernatants (n=16) contained neither LTs or SAgs. Functionally, SAg-SNs behaved like purified staphylococcal enterotoxin A (SEA) or SEB tested in parallel. The absence of SAg-like activity in LT-SNs was confirmed by heat treatment of LT-SNs, which destroyed the leukocytotoxic activity, but did not reveal any MNC-activating potential. This study, therefore, suggests, that pathogenic S. aureus isolates either produce leukotoxins or superantigens and that both groups of virulence factors can easily be differentiated by the functional assays described. The prevalence of leukotoxin- or superantigen-producing isolates was comparable among cattle with subclinical (LT=41%; SAg=30.8%) mastitis. The higher frequency of LT-producing isolates in cases of clinical mastitis (LT=55.2%; SAg=27.6%) was not significant. At least, these findings argue against the dominant role of superantigens or leukotoxins in S. aureus-induced bovine mastitis.

BOVIGAM: an in vitro cellular diagnostic test for bovine tuberculosis

BOVIGAM which is based on the detection of gamma interferon (IFN- gamma) is a rapid, laboratory assay of a cell mediated immune response that may be used for the detection of tuberculosis (TB) infection in animals. Whole blood is first incubated overnight with bovine PPD, avian PPD or negative control antigens, and IFN- gamma in the supernatant plasma is then measured by EIA. TB infection is indicated by a predominant IFN- gamma response to bovine PPD. Since 1988, BOVIGAM has been extensively trialed on more than 200 000 cattle in Australia, Brazil, Ireland, Northern Ireland, Italy, New Zealand, Romania, Spain and the USA. Sensitivity has varied between 81.8% and 100% for culture-confirmed bovine TB and specificity between 94% and 100%. The IFN- gamma assay detects M. bovis infection earlier than the skin test and in New Zealand is applied to detect skin-test negative cattle with TB, where after slaughter a significant number of IFN- gamma reactors have TB. BOVIGAM is also approved in New Zealand for serial testing skin test positive cattle when non-specificity is suspected. Cattle are tested 7-30 days after a positive caudal fold test. The boosting effect of the skin test on T-cell activity allows blood to be cultured with PPD up to 30 h after collection without effecting accuracy. The BOVIGAM results are not affected by poor nutritional condition and are only mildly and briefly affected by dexamethasone treatment and parturition. IFN- gamma responses of cattle vaccinated with BCG are dose-dependent and short-lived. The BOVIGAM kit is now used routinely in many countries for the detection of M. bovis infected cattle, buffalo and goats.

Tumor necrosis factor alpha and its receptors in experimentally bovine leukemia virus-infected sheep

To examine whether tumor necrosis factor alpha (TNF alpha) contributes to the pathogenesis of bovine leukemia virus (BLV) infection, the mRNA expression patterns of TNF alpha and its receptors, type 1 (TNF R1) and type 2 (TNF R2) were investigated. Sheep inoculated with BLV were divided into two groups; one was BLV-positive and the other BLV-negative based on the detection in peripheral blood mononuclear cells (PBMC). Expression of TNF R1 mRNA was down-regulated in PBMC from the BLV-positive compared to BLV-negative sheep. No difference was shown in the expression levels of TNF R2 mRNA between the two groups. Furthermore, proliferative responses of PBMC in the presence of TNF alpha were observed from the BLV-positive, but not BLV-negative sheep. Membrane-bound TNF alpha (mTNF alpha) is thought to be one of the ligands, inducing B-cell activation. Flow cytometric analysis demonstrated that the number of PBMC, that were positive for mTNF alpha expression, was increased in the BLV-positive sheep. Thus, the expression of TNF alpha and its receptors may be closely associated with lymphocytosis induced by BLV.

Purified bovine WC1+ gamma delta T lymphocytes are activated by staphylococcal enterotoxins and toxic shock syndrome toxin-1 superantigens: proliferation response, TCR V gamma profile and cytokines expression

In this study, the ability of purified bovine gammadelta T cells in vitro to be activated by superantigens (SAg) was investigated. Freshly isolated WC1(+) gammadelta T cells, in the presence of autologous glutaraldehyde-fixed or gamma-irradiated antigen presenting cells (APC) and IL-2, were incubated with staphylococcal enterotoxins A and B (SEA and SEB), and toxic shock syndrome toxin-1 (TSST-1). Both a proliferative response and the expression of particular T cell receptor genes of the gamma variable (TCR Vgamma) repertoire family were induced. Genes encoding TCR Vgamma1 and TCR Vgamma2 family, but not TCR Vgamma5 were detected. The cells also expressed cytokine transcripts, namely, those of IL-12, IFN-gamma and TNF-alpha, but not IL-2, IL-4, IL-6, IL-7 and IL-10. The activation and proliferation of freshly isolated gammadelta T cells by non-processed antigens required two signals, one originating from the APC and a second dependent on exogenous IL-2. Our results show that purified bovine WC1(+) gammadelta T cells could be driven to proliferate and to express a particular TCRVgamma profile in response to superantigen activation. The possible implication of cytokines expressed by bovine gammadelta T cells in immunopathogenesis is discussed.

Interaction of staphylococcal toxic shock syndrome toxin-1 and enterotoxin A on T cell proliferation and TNFα secretion in human blood mononuclear cells

BACKGROUND

The majority of menstrual toxic shock syndrome (MTSS) cases are caused by a single clone of Staphylococcus aureus that produces both toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin A (SEA).

OBJECTIVE

To determine whether the two superantigens interact to cause an enhancement of biological activity in human peripheral blood mononuclear cells (PBMCs).

DESIGN

PBMCs from nine healthy donors were stimulated with TSST-1 or SEA, either alone or in combination at their minimum effective concentrations.

SETTING

In vitro study.

INTERVENTIONS

Human PBMCs were stimulated in vitro with TSST-1 (1 pg/mL), SEA (0.1 pg/mL) or combination for 20 to 72 h. Mitogenic response was determined by [(3)H]-thymidine incorporation. PBMC culture supernatants were assayed for the presence of tumour necrosis factor-alpha (TNFα), interleukin (IL)-1β and IL-6 by ELISA.

MAIN RESULTS

The combination of TSST-1 and SEA induced significantly greater mitogenesis in human PBMCs compared with either toxin alone (P<0.05, paired Student's t test, two-tailed). Similarly, the production of TNFα in culture supernatants was significantly greater in the combination of TSST-1 and SEA compared with either TSST-1 or SEA alone (P<0.05). In contrast, no enhancement in the levels IL-1 or IL-6 was observed.

CONCLUSIONS

These data suggest that the co-production of TSST-1 and SEA by S aureus may provide some biological advantage to the organism throughs an enhanced effect of these superantigens on T cell activation and TNF secretion.

Activation of bovine lymphocyte subpopulations by staphylococcal enterotoxin C

Staphylococcus aureus is a major mastitis-causing pathogen in cattle. The chronic nature of bovine staphylococcal mastitis suggests that some products or components of S. aureus may interfere with the development of protective immunity. One class of molecules that could be involved are superantigens (SAgs). Although a significant number of mastitis isolates produce SAgs, the effect of these molecules on the bovine immune system is unresolved. To determine if immunosuppression caused by SAgs could play a role in pathogenesis, we monitored bovine lymphocytes exposed to staphylococcal enterotoxin C1 (SEC1). Activation of bovine lymphocytes by either SEC1 or concanavalin A (ConA) was influenced by the gammadelta/alphabeta T-cell ratio in the culture. Compared to ConA-induced stimulation, cultures stimulated with SEC1 generated small numbers of CD4+ alphabeta T cells expressing high levels of interleukin-2 receptor alpha chain (IL-2R alpha) and major histocompatibility complex class II (MHCII), suggesting that SAg exposure does not lead to full activation of these cells. This state of partial activation was most pronounced in cultures with a high gammadelta/alphabeta ratio. In contrast, significant numbers of CD8+ alphabeta T cells expressed high levels of IL-2R alpha and MHCII, regardless of the gammadelta/alphabeta ratio and the stimulant used. CD8+ blasts in cultures stimulated with SEC1 also expressed another activation marker, ACT3, previously detected predominantly on thymocytes and CD4+ T cells. Although gammadelta CD2- and CD2+ T cells expressed MHCII and IL-2R alpha following stimulation with SEC1, only a few cells increased to blast size, suggesting that they were only partially activated. The results suggest ways in which SAgs might facilitate immunosuppression that promotes the persistence of bacteria in cattle and contributes to chronic intramammary infection.

Elevated levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) activities in the sera and milk of cows with naturally occurring coliform mastitis

The presence of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) activities was determined in milk and serum of cows with naturally occurring coliform mastitis (CFM). TNF-alpha was detected in the sera from 26 of 32 cows with CFM. TNF-alpha levels were higher in the sera than in the milk. IL-6 was high in the sera of surviving CFM animals, but was low in animals that died and in healthy controls. Furthermore, the mean level of IL-6 was 20-fold higher in the milk than in the sera of mastitic cows. The level of IL-6 in the serum was correlated to that in the milk in individual animals. The presence of IL-6 and TNF-alpha in the sera appears to relate to severe clinical condition of CFM, in the milk whereas they may play a role in generating inflammation of the mammary gland.