Staphylococcal Enterotoxin A Acts through Nitric Oxide Synthase Mechanisms in Human Peripheral Blood Mononuclear Cells To Stimulate Synthesis of Pyrogenic Cytokines

Abstract

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 V␤s 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...

Blocking NF-κB Activation May Be an Effective Strategy in the Fever Therapy

“…The animals were permitted at an ambient temperature of 22°C for at least 90 min to obtain thermal balance before drugs were administered. Temperature responses were assessed as changes from preinjection value (⌬°C) and the fever index (FI), the area under the curve produced in the 5-h period after the injection of LPS, in terms of degrees centigrade per 5 h was calculated [15]. Results were expressed as the meansϮstandard errors of the means (SEM) for experiments.…”

“…At first, experiments were carried out to assess the pyrogenic response in rabbits to the intravenous injection of supernatant fluids obtained from human PBMC incubated with LPS alone or LPS plus NF-B inhibitors, including pyrrolidine dithiocarbamate (PDTC) [6,7], curcumin (Cur) [8], sodium pyrithione (Pyri) [9], or Nacetyl-L-cysteine (NAC) [10]. Second, we assessed the effects of the pretreatment of rabbits with an intravenous dose of either PDTC, Cur, Pyri, or NAC on both the fever and/or the levels of IL-1␤, IL-6, and TNF-␣ in the serum of rabbits after an intravenous administration of LPS.…”

The Staphylococcal Enterotoxins

“…SEA together with an anti-SEA antibody actually increase TNFa and IL-6 secretion by macrophages, and this is thought to be due to cross-linking macrophage MHC I receptors (Wright and Chapes, 1999). Targeting of the NOS mechanism has been successful with aminoguanadine (Won et al, 2000) and niacinimide (LeClaire et al, 1996).…”

Platonin, a Cyanine Photosensitizing Dye, Inhibits Pyrogen Release and Results in Antipyresis

“…Temperature responses were assessed as changes from the pre-injection value (D°C) and/ or the fever index (FI), the area under the curve produced in the 2-h period after the injection of LPS, in terms of degrees centigrade per 2 h were calculated (10). Results were expressed as the means ± S.E.M.…”