Pyrogenic toxins of Staphylococcus aureus in sudden unexpected nocturnal deaths in adults and older children: factors influencing the control of inflammatory responses to toxic shock syndrome toxins

Abstract

Sudden unexpected nocturnal deaths (SUND) occur in young immigrant workers, mainly from south-east Asia, who are employed in countries such as Singapore and Saudi Arabia. Pyrogenic toxins of Staphylococcus aureus have been identified in two cases of sudden unexpected death in adults in the UK and it has been suggested that these or other toxins with superantigen properties might induce strong inflammatory responses leading to sudden unexpected nocturnal deaths. The objectives of the present study were (1) to assess the levels of antibodies to pyrogenic staphylococcal toxins in the general population, (2) to assess the levels of IgG to the toxins needed to reduce the production of inflammatory mediators by 50% in a model system, (3) to assess in a model system the effects on inflammatory responses to toxic shock syndrome toxin-1 (TSST) of cortisol levels present at night, during the day and under conditions of physiological stress. Enzyme linked immunosorbent assays were used to assess levels of IgG to TSST, staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin C (SEC). Human buffy coats were used to examine the effect of IgG to the toxins for neutralising activity and the effect of cortisol on induction of inflammatory mediators. Tumour necrosis factor α (TNF-α) was detected by a bioassay with L929 cells, interleukin-6 (IL-6) and interleukin-10 (IL-10) were measured by an enzyme linked immunosorbent assay. IL-6 and TNF-α levels elicited by the toxins were not reduced by night time levels of cortisol (5–10 μg dl −1) levels. Day time levels of cortisol (10–20 μg dl −1) significantly inhibited IL-6 production but not TNF-α in responses. Stress levels of cortisol (40–80 μg dl −1) significantly reduced all three cytokines earlier than the normal day time levels. The majority of the population tested had sufficient antibodies to reduce TNF-α and IL-6 responses elicited by TSST and SEC in the model system. In the age range in which most sudden unexpected nocturnal death cases occur (20–39 years), males had significantly lower levels of IgG to TSST compared with females. If these toxins play a role in precipitating the series of events leading to sudden unexpected nocturnal death, the higher levels of IgG to the toxins observed in females might explain partly the much higher prevalence of these deaths among men in this age range. If inflammatory responses play a role in sudden unexpected nocturnal death, the inability of the night time levels of cortisol to control IL-6 and TNF-α in the model system might reflect these interactions in vivo. The methods developed for detection of the toxins in tissue samples and the quantitative IgG assays for anti-toxins can be applied to investigation of SUND victims to test the hypothesis that some of these deaths are precipitated by pyrogenic staphylococcal toxins.