The staphylococcal enterotoxins (SE) are secreted by a variance of Staphylococcus aureus and cause most common staphylococcal food poisoning and staphylococcus-associated toxic shock syndrome in humans and primates (1,9,15,17,19). The SE are classified into different toxin serotypes, such as SEA, SEB, SEC1, SEC2, and SEE (30). The SE, S. aureus toxic shock syndrome toxin 1, and group A streptococcal pyrogenic exotoxins are commonly considered superantigens because of their effects on the immune system (12,14). The SE are 26-to 30-kDa proteins that bind with major histocompatibility class II molecules on antigen-presenting cells and stimulate T cells bearing Vs on their receptor variable region (1, 5, 7). Intravenous administration of SEA is shown to produce fever, lethargy, shock, and death in cats, rabbits, and monkeys (3,9,17,23,26). In addition, our recent results demonstrate that the febrile responses are associated with increased levels of circulating interleukin-2 (IL-2), interferon (IFN), and tumor necrosis factor (TNF) in rabbits.Other lines of evidence have shown that macrophages, neutrophils, endothelial cells, and hepatocytes are able to synthesize nitric oxide (NO) from L-arginine (24). Using arginine analogues such as N G -monomethyl-L-arginine and aminoguanidine (AG) to inhibit NO production, investigators have shown that NO mediates a variety of physiological events ranging from neurotransmission to the antimicrobial activity exhibited by mononuclear phagocytes in vitro (20). Our recent results have also demonstrated that febrile responses induced by intravenous injection of SEA are attenuated by pretreatment with AG (11). However, it was not known whether the NO pathway in peripheral blood mononuclear cells (PBMC) represent an important mechanism for modulation of SEA-induced synthesis or release of pyrogenic cytokines. In order to address the question properly, experiments were carried out to assess the pyrogenic responses in rabbits to intravenous injection of supernatant fluids obtained from PBMC treated with SEA alone or SEA plus inhibitors of NO synthase such as AG and dexamethasone (8,27). At the same time, levels of IL-1, TNF, IFN-␥, IL-2, and IL-6 in the supernatant fluids were assessed in vitro. Furthermore, the effects of adding the anti-IL-1, anti-TNF-␣, and anti-IFN-␥ monoclonal antibody (MAb) to the supernatant fluids from SEA-treated human PBMC on the pyrogenic responses to intravenous administration of the supernatant fluids were assessed in rabbits.
MATERIALS AND METHODS
Preparation of PBMC.Human PBMC were obtained from freshly collected buffy coat fractions from healthy donors at the Tainan Blood Bank Center (Tainan City, Taiwan, Republic of China). They were isolated by centrifugation over a Ficoll-Paque (Pharmacia, Uppsala, Sweden) density gradient at room temperature for 30 min in a Sorvall RT6000B (DuPont). The cells collected at the interface were washed three times with serum-free RPMI 1640 (GIBCO BRL, Grand Island, N.Y.) and subsequently resuspended in serum-free AIM-V...