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Certain strains of Staphylococcus aureus express one or both of two related, but immunologically distinct, exfoliative toxins (ETA and ETB). These toxins induce the symptoms associated with staphylococcal scalded skin syndrome. Both ETs have been shown to stimulate T cell proliferation. Recently, it was reported that ETA is a superantigen that stimulates T cells bearing human Vbeta2 or several murine Vbetas. However, other investigators have proposed that the superantigenicity reported for ETA resulted from contaminants in commercial preparations. This present study addresses those conflicting reports by assessing the biological and immunologic activities of highly purified rETs. ETA and ETB required APCs to induce selective polyclonal expansion of several human Vbetas (huVbetas), although, neither toxin expanded huVbeta2. ETB induced expansion of murine T cells bearing Vbetas 7 and 8, those that have the highest homology to the huVbetas expanded by ETA and ETB. Although flow cytometry of ETB-stimulated T cells matched PCR results, stimulation by ETA reduced percentages of T cells positive for several huVbetas that had been shown to have increased levels of mRNA transcripts. ETA and ETB induced contrasting reactions in vivo. In rabbits, ETB was moderately pyrogenic and enhanced susceptibility to lethal shock, while ETA lacked both activities. Predictions based on comparisons with other superantigens suggest molecular regions potentially involved in receptor binding in the ETA crystal structure and a modeled ETB three-dimensional structure. These results show that ETs are superantigens with unique properties that could account for the discrepancies reported.

Persistent intramammary infections of dairy cows with Staphylococcus aureus may involve immunosuppression mediated by bacterial toxins such as enterotoxins and other super-antigens (SAgs). Previously we found that stimulation of bovine PBMC with staphylococcal enterotoxin C (SEC) induced a unique phenotype of activated CD8+ T cells expressing a newly identified activation molecule, ACT3. In the present study we found that SEC induced the expression of interleukin (IL)-4 and IL-10 mRNAs, two cytokines associated with type 2 responses. Elevated levels of IL-4 and IL-10, observed between day 0 and day 4 of culture, were associated with temporary inhibition of proliferative responses of T cells, evidenced by a decrease in numbers of CD4+ T cells and a small increase in numbers of CD8+ T cells. Vigorous proliferation of T cells occurred between days 4 and 7 of culture and with a bias towards CD8+ T cells. Acquisition of the ACT3+ phenotype by CD8+ T cells was preceded by induction of IL-4 mRNA. Thus, in the bovine system, SAgs may hinder protective responses by inducing type 2 cytokines, which interfere with immune clearance of many microbial pathogens. The results of the study are consistent with the hypothesis that SAgs are involved in immunosuppression, and suggest possible immunomodulatory mechanisms.

There is a need for experimental systems allowing study of host responses generated by continuous, low-level exposures to parasites. To assess the pulmonary inflammatory responses in different types of exposure to infection we used bronchoalveolar lavage (BAL). Rats sensitized by 500 Nippostrongylus brasiliensis larvae given in 20 doses over a 4-wk period (group T) and challenged with 500 larvae 33 days after the initial exposure were compared to rats initially given 1 sensitizing dose of 500 larvae (group B) and also to naive, sham-treated (group S) rats, subsequently challenged with 500 larvae. BAL performed prior to final challenge revealed markedly increased numbers of macrophages and eosinophils in group T, but there were only minor changes in numbers of these cells in group B. After final challenge, numbers of BAL macrophages and eosinophils were greater in group T than in group B, although in group B there was a rapid increase in numbers of these cells. Changes in numbers of BAL neutrophils were not correlated with previous sensitization to N. brasiliensis. Thus, there was a pronounced influx of leucocytes into the pulmonary lumen after secondary challenge in rats sensitized by repeated exposures to low doses of larvae.

Broncho-alveolar lavage (BAL) has become a routine method of sampling airway and alveolar milieu. Variations of BAL techniques, such as application of chest massage, may have an effect on cell yields. We compared numbers and composition of cells obtained by BAL with and without chest massage from naive rats and from rats infected 7 days earlier with 3,000 larvae of Nippostrongylus brasiliensis. Both techniques revealed significant increases in numbers of agranulocytes and granulocytes after N. brasiliensis infection, but the total yield of cells was 4-5 times greater when massage was used. The use of massage consistently increased the yield of macrophages, but did not result in consistently greater yields of lymphocytes or granulocytes.

The effects of exposure of rats to repeated low-level (trickle) infections with Nippostrongylus brasiliensis were assessed by measuring intestinal and lung worm burdens. Worm recoveries from the intestine, made during a period of trickle infection in rats of different ages, showed a virtually complete rejection of intestinal worms in old rats and a partial rejection in young rats. Recoveries from lungs were made in young rats after challenge infection with 500 third-stage (L3) larvae, given after a 2- or 4-wk period of sensitization, during which rats were infected with 10 or 20 doses of 25 larvae. Such trickle infections elicited a strong host response to a challenge infection, manifested by low recoveries of larvae and an increased duration of larval retention in lungs. In another group of rats sensitized by a single dose of 250 L3 larvae, the recovery of larvae from challenge infection and their clearance from the lungs were similar to these observed in rats uninfected prior to challenge. The effect of trickle infections on preintestinal stages was most pronounced and consistent in rats exposed to larvae the greater numbers of times and over the longest period.

There is a need for experimental systems allowing study of host responses generated by contin- uous, low-level exposures to parasites. To assess the pulmonary inflammatory responses in different types of exposure to infection we used bronchoalveolar la- vage (BAL). Rats sensitized by 500 Nippostrongylus brasiliensis larvae given in 20 doses over a 4-wk period (group T) and challenged with 500 larvae 33 days after the initial exposure were compared to rats initially giv- en 1 sensitizing dose of 500 larvae (group B) and also to naive, sham-treated (group S) rats, subsequently challenged with 500 larvae. BAL performed prior to final challenge revealed markedly increased numbers of macrophages and eosinophils in group T, but there were only minor changes in numbers of these cells in group B. After final challenge, numbers of BAL mac- rophages and eosinophils were greater in group T than in group B, although in group B there was a rapid increase in numbers of these cells. Changes in numbers of BAL neutrophils were not correlated with previous sensitization to N. brasiliensis. Thus, there was a pro- nounced influx of leucocytes into the pulmonary lumen after secondary challenge in rats sensitized by repeated exposures to low doses of larvae.

The effects of exposure of rats to repeated low-level (trickle) infections with Nippostrongylus brasiliensis were assessed by measuring intestinal and lung worm burdens. Worm recoveries from the intestine, made during a period of trickle infection in rats of different ages, showed a virtually complete rejection of intestinal worms in old rats and a partial rejection in young rats. Recoveries from lungs were made in young rats after challenge infection with 500 third-stage (L3) larvae, given after a 2- or 4-wk period of sensitization, during which rats were infected with 10 or 20 doses of 25 larvae. Such trickle infections elicited a strong host response to a challenge infection, manifested by low recoveries of larvae and an increased duration of larval retention in lungs. In another group of rats sensitized by a single dose of 250 L3 larvae, the recovery of larvae from challenge infection and their clearance from the lungs were similar to these observed in rats uninfected prior to challenge. The effect of trickle infections on preintestinal stages was most pronounced and consistent in rats exposed to larvae the greater numbers of times and over the longest period.