Staphylococcus aureus Enterotoxin D Is Secreted in Milk and Stimulates Specific Antibody Responses in Cows in the Course of Experimental Intramammary Infection

Abstract

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.Staphylococcus aureus is a major cause of intramammary infection in ruminants and is a causative agent of a range of human and animal diseases. S. aureus mastitis tends to commence with an acute clinical episode which subsequently develops to become a chronic infection (1). The cure rate after antibiotic therapy is low (42). The chronic nature of bovine staphylococcal mastitis and the ability of the bacteria to withstand strong inflammatory responses may be associated with an impairment of the immune response mediated by factors secreted by S. aureus (39).S. aureus produces a family of related superantigens (SAgs) that includes several staphylococcal enterotoxins (SE) and toxicshock-syndrome toxin (TSST) variants (6). Staphylococcal SAgs are prototypical microbial superantigens, characterized by their ability to bind to major histocompatibility complex class II molecules and specific V␤ segments of ␣␤ T-cell receptors (32). SAgs bypass the antigenic specificities of T-cell receptors and stimulate abnormally large numbers of T cells. At extremely low concentrations, these molecules can induce profound disturbances in the homeostasis of the immune system (17, 44). These toxins play a critical role in human toxic shock syndrome and food poisoning, but their possible role in the onsets or maintenance of other diseases is not well understood (41).Geographical differences exist in the occurrence of SAg-producing strains causing mastitis (22). Kenny et al. (19) found that S. aureus strains producing enterotoxin D (SED) alone or in combination with S. aureus enterotoxin C (SEC) and TSST-1 accounted for 22% of the isolates from New York State. In Norway, a previous study showed that 58% of S. aureus isolates expressed SAgs and that the production of SEC and TSST-1 in combination predominated (40). Some reports have suggested that S. aureus...

Cow-to-cow variation in fibroblast response to a toll-like receptor 2/6 agonist and its relation to mastitis caused by intramammary challenge with Staphylococcus aureus

“…In agreement with other experimental challenge models (Bourry and Poutrel, 1996;Tollersrud et al, 2006), there was an increase in anti-S. aureus total IgG present in whey and plasma, and both IgG 1 and IgG 2 observed in the whey from the HR animals. However, elevated concentrations of strain-specific antibodies did not offer an advantage in pathogen clearance for the HR animals.…”

Staphylococcus aureusleucotoxin LukM/F' is secreted and stimulates neutralising antibody response in the course of intramammary infection

“…This suggests that chronic infections, mainly subclinical, elicit Ab responses to leucotoxins also in cattle. A parallel can be made with another potential virulence factor of mastitis-causing S. aureus, enterotoxin D. This enterotoxin was recently shown to be produced in vivo and was found in the milk of a few infected cows, at concentrations active on bovine lymphocytes [19]. Specific Ab were elicited, which were able to neutralize the toxin.…”

Induction of Immunosuppressive CD8+CD25+FOXP3+ Regulatory T Cells by Suboptimal Stimulation with Staphylococcal Enterotoxin C1

“…The causal link of SAgs in the pathogenesis of toxic shock syndrome and food poisoning, in which large amounts of SAgs (1–100 μg/ml) are produced, is well established (4, 11). However, relatively small concentrations of SAgs (0.65 – 5 ng/ml) are produced in more frequently occurring asymptomatic colonization or chronic S. aureus infections (12–14), but the biological relevance of such small concentrations of SAgs in the pathogenesis of S. aureus is not fully understood.…”