Infectious agents, the inflammatory responses of infants and sudden infant death syndrome (SIDS)

The Science (or Nonscience) of Research Into Sudden Infant Death Syndrome (SIDS)

This Viewpoint paper presents a timely and constructive critique of mainstream SIDS research. It is concerning that twenty-first century medical science has not provided an answer to the tragic enigma of SIDS. The paper helps explain why this is so and illustrates possible shortcomings in the investigation of Sudden Infant Death Syndrome/Sudden Unexplained Infant Death (SIDS/SUID) by mainstream researchers. Mainstream findings are often based on questionable and dogmatic assumptions that return to founding notions such as the Triple Risk Hypothesis and the contention that the mechanisms underlying SIDS/SUID are heterogeneous in nature. The paper illustrates how the pathological findings in SIDS have been under-investigated (or ignored) and that key epidemiological risk factors have slipped from memory. This apparent amnesia has resulted in failure to use these established SIDS facts to substantiate the significance of various neuropathological, neurochemical, or other research findings. These unsupported findings and their derivative hypotheses are therefore ill-founded and lack scientific rigor.

CONCLUSION

The deficits of SIDS "science" revealed in this paper explain why the SIDS enigma has not yet been solved. To make progress in understanding SIDS, it is important that researchers, as scientists, uphold standards of research. Encouragement for new directions of research is offered.

SIDS, prone sleep position and infection: An overlooked epidemiological link in current SIDS research? Key evidence for the "Infection Hypothesis"

Mainstream researchers explain the etiology of SIDS with the cardiorespiratory paradigm. This has been the focus of intense study for many decades without providing consistent supporting data to link CNS findings to epidemiological risk factors or to the usual clinicopathological findings. Despite this, and the apparent oversight of the link between prone sleep position and respiratory infection, papers citing CNS, cardiac and sleep arousal findings continue to be published. Discovery of the prone sleep position risk factor provided tangential support for the cardiorespiratory control hypothesis which defines the mainstream approach. Despite many decades of research and huge expenditure, no aetiological answer has been forthcoming. In asking why?This paper exposes some of the shortcomings regarding this apparent oversight by mainstream SIDS researchers and examines the role of respiratory infection and puts the case for the “Infection Hypothesis.” In addition, the paper provides encouragement to neuropathologists to examine the potential link between CNS findings and cardiac function (as opposed to respiratory function) in relation to infection and to examine possible correlates between CNS findings and established risk factors such as recent infection, contaminated sleeping surfaces, maternal/obstetric/higher birth, ethnicity, non-breast-feeding, male gender, etc. or with the usual gross pathological findings of SIDS (intrathoracic petechial hemorrhages, liquid blood, congested lungs). The shortcomings exposed through this review invite questions over current research directions and hopefully encourage research into other more plausible hypotheses, such as the infection paradigm.•

Mainstream SIDS researchers appear to have overlooked the key relationship between prone sleep position and infection.

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This omission has major implications for current and future SIDS research.

Candidate gene variants of the immune system and sudden infant death syndrome

BACKGROUND

Sudden infant death syndrome (SIDS) causes early infant death with an incidence between 0.5 and 2.5 cases among 1000 live births. Besides central sleep apnea and thermal dysregulation, infections have been repeatedly suggested to be implicated in SIDS etiology.

METHODS

To test the risk contribution of common genetic variants related to infection, we genotyped 40 single-nucleotide polymorphisms (SNPs) from 15 candidate genes for association with SIDS in a total of 579 cases and 1124 controls from Germany and the UK in a two-stage case control design.

RESULTS

The discovery-stage series (267 SIDS cases and 303 controls) revealed nominally significant associations for variants in interleukin 6 (IL6) (rs1880243), interleukin 10 (IL10) (rs1800871, rs1800872), and mannose-binding lectin 2 (MBL2) (rs930506), and for several other variants in subgroups. Meta-analyses were then performed in adding genotype information from a genome-wide association study of another 312 European SIDS cases and 821 controls. Overall associations were observed for two independent variants in MBL2: rs930506 in a co-dominant model (odds ratio (OR) = 0.82, p = 0.04) and rs1838065 in a dominant model (OR = 1.27, p = 0.03).

CONCLUSION

Our study did not replicate published associations of IL10 variants with SIDS. However, the evidence for two independent MBL2 variants in the combined analysis of two large series seems consistent with the hypothesis that infection may play a role in SIDS pathogenesis.

Use of proteinase K for RT-PCR of cytokine mRNA in formalin fixed tissue

Fresh tissue from cases of sudden infant death syndrome is becoming increasingly scarce and therefore researchers interesting in studying the aetiology of this syndrome have had to resort to archival tissue, usually in the form of paraffin wax sections. A simple method for isolating mRNA from formalin fixed, paraffin wax embedded material of sufficient purity for reverse transcription (RT)-PCR is described. Proteinase K treatment of formalin fixed, wax embedded tissue followed by RNA STAT-60 extraction was successful in isolating mRNA suitable for RT-PCR. Interleukin (IL)-1alpha, IL-6 and tumour necrosis factor (TNF) transcripts were amplified successfully from heart, but not thyroid, kidney or liver tissue, of a patient who died following rejection of a transplanted heart, and IL-1alpha, but not IL-6 or TNF, transcripts from lung tissue of a six month old baby who died of viral pneumonia. Transcripts of a housekeeping gene were detected in all tissues. This method should be useful for examining gene expression in archival material.

Virological analysis in the diagnosis of sudden children death: A medico-legal approach

Infections are considered to be an important cause of unexpected death in children. It has also been assumed that respiratory viruses are involved in the genesis of sudden infant death syndrome (SIDS). The Spanish National Institute of Toxicology and Forensic Sciences act as the forensic reference centre for Spain. We analyse the experience of this centre in the virological study of 64 cases of sudden children death where viral serology, virological cultures, herpesviruses polymerase chain reaction (PCR) and electron microscopy were performed. According to pathological findings, death could only be attributed to an adenovirus infection in one amygdalitis with upper airways stenosis and asphyxia. Human herpes virus 6 (HHV-6) was detected by PCR in one case with pathological findings characteristic of SIDS. Recent infection by respiratory syncytial virus (RSV), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were also detected. Meanwhile, 85.9% of the cases yielded negative viral results. Twenty-eight infants were finally categorised as SIDS. Pathological findings of infection were detected in 12 patients despite the negativity of viral analyses. Although viral infection is an uncommon cause of sudden children death, a complete microbiological investigation will help to solve the puzzle of SIDS. Definitive guidelines for microbiological analyses need to be updated whilst new pathogens are discovered or new techniques are implemented in order to clarify unsolved cases.

Sudden infant death syndrome: overview and update

The past decade and a half has seen marked changes in the epidemiology of sudden infant death syndrome (SIDS). The avoidance of certain risk factors such as sleeping prone and cigarette smoke exposure has resulted in the death rate falling dramatically. Careful evaluation of environmental factors and endogenous characteristics has led to a greater understanding of the complexities of the syndrome. The development and implementation of death scene and autopsy protocols has led to standardization in approaches to unexpected infant deaths with increasing diagnoses of accidental asphyxia. Despite these advances, there is still confusion surrounding the diagnosis, with deaths being attributed to SIDS in many communities and countries where death scene investigations and autopsies have not been conducted. The following review provides a brief overview of the historical background, epidemiology, pathology, and pathogenesis of SIDS. Contentious issues concerning the diagnosis and current problems are discussed. Despite calls to abandon the designation, SIDS remains a viable term for infants who die in their sleep with no evidence of accident, inflicted injury, or organic disease after a full investigation has been conducted according to standard guidelines.

Increase of pulmonary density of macrophages in sudden infant death syndrome

A 1996 cytodensitometric study found increased cellular density in the pulmonary parenchyma of infants who died of sudden infant death syndrome (SIDS). The present study clarifies these results in quantifying the density of immunohistochemical subtyped inflammatory cells. Histomorphometry was used to compare the density of macrophages, granulocytes and T and B lymphocytes in the lungs of two groups of infants. From the post-mortem records of infant deaths between 1983 and 1995, 29 (mean age = 5 months) were randomly selected including 16 cases of SIDS and 13 who died of other non-pulmonary causes. Densities of immunoreactive cells were measured under blind conditions in the parenchyma. The mean density of macrophages was significantly higher in cases of SIDS compared with the controls (P = 0.0318), but there were no differences for the lymphocytes and the granulocytes. These morphometrical results must be interpreted within the methodological limits of this study, especially the non-uniform level of lung inflation between selected subjects. However, the differences in level of inflation are not sufficient to explain the observed increase of macrophage density. Indeed, the mean values of alveolar surface area, which represent an indirect measure of lung inflation, are not significantly different between the two groups. Increase of pulmonary macrophage density in SIDS agrees with three non-exclusive hypotheses: (1) an abnormal inflammatory reaction by expression of Th1 helper cell phenotype activation; (2) consequence of passive smoking; and (3) post-agonal mechanisms. Bacterial superantigens produced by toxigenic bacteria in the respiratory tract could play a role as a trigger factor that initiates a fatal cascade with overproduction of cytokines leading to death. The significant increase of pulmonary macrophage density would be the morphological expression of this potential mechanism of death.

Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life

Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus.

Microbiology in sudden infant death syndrome (SIDS) and other childhood deaths

The usefulness of post-mortem microbiology in the assessment of sudden unexpected deaths in infants and children has been debated by many pathologists. In our centre, microbiological investigations have been part of the post-mortem protocol for investigation of sudden deaths in infants and children for the past 12 years. The objective of this study was to review the microbiological findings for infants and children examined by our unit during the past 4 years in relation to gross and histological findings of the autopsy and the medical and social histories of the children. We reviewed 57 consecutive sudden deaths in infants and children examined by our Referral Centre between November 1994 and October 1998. These 57 sudden deaths were aged from 1 day to 4 years and 9 months including 40 cases of sudden infant death syndrome (SIDS) and 17 non-SIDS deaths. Results of the microbiological investigations of tissues and body fluids were assessed during the case review with reference to histological shock signs, severe gastric aspiration, and signs of acute thymic involution. Bacteria alone or in association with viruses were identified in 45/57 (79%) cases including 34/40 (85%) SIDS. The most frequent bacterial isolate was Escherichia coli (27), and the virus identified most frequently was enterovirus (8). C-reactive protein was increased in 10 out of the 42 cases tested including 8/32 (25%) SIDS. Significant gastric content aspiration was found in 17/57 (29.8%) including 13/40 (32.5%) SIDS. Histological signs of shock were present in 33/55 (60%) cases including 22/39 SIDS (56.4%). The microbiological findings were positive for 27/33 (81.8%). We conclude that post-mortem microbiology is essential in sudden death investigation. The conclusion that a death is unexplained if no microbiology was done is not valid, even if in some cases it may be difficult to know precisely in what way the pathogen contributed to the death.

Inflammatory responses in sudden infant death syndrome -- past and present views

Sudden infant death syndrome (SIDS) is sudden unexpected death in infancy for which there is no explanation based on commonly accepted diagnostic criteria; however, half of the victims have had slight signs of infection prior to death. Such slight infection with fever is an important risk factor in combination with a prone sleeping position, especially in infants between 2 and 4 months of age. The purpose of this review is to summarise findings that support the theory that a significant part of cot deaths may be due to an overreaction to otherwise harmless infections. Such factors are mucosal immune stimulation, cytokines in the cerebrospinal fluid and hypoxanthine levels in vitreous humour. The review aims at explaining why we believe that a slight infection combined with a prone position, a warm environment and a vulnerable age period may trigger a vicious circle leading to death.

The effect of prone posture on nasal temperature in children in relation to induction of staphylococcal toxins implicated in sudden infant death syndrome

The incidence of sudden infant death syndrome (SIDS) has declined in response to campaigns discouraging the prone sleeping position. Recent work suggests some SIDS death may be in response to bacterial toxins produced in the upper airway. A minimal temperature of 37 degrees C is required for induction of the pyrogenic toxins of Staphylococcus aureus identified in many SIDS infants. This aim of this study was to test the hypothesis that the prone position raises the temperature of the upper airways in children. A pilot study of 10 children (aged 3-8) and a main study of 30 children were carried out. Nasal septal temperatures were measured with an infra-red thermometer with the subjects in upright and prone positions under controlled conditions of ambient temperature and humidity. In both the pilot study and main study, nasal temperatures in the prone position were significantly higher (P < 0.01) Five subjects' prone readings were 37 degrees C or higher. These findings suggest that lying prone raises the upper airway surface temperature towards that required for toxin production. This could be one means by which the prone sleeping position contributes to the risk of SIDS.

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): I. The effect of human milk and infant formula preparations on binding of toxigenic Staphylococcus aureus to epithelial cells

Epidemiological studies indicate that breast-fed infants are at a decreased risk of sudden infant death syndrome (SIDS) compared to formula-fed infants. Increasing evidence suggests that infectious agents might be involved in some of these deaths, in particular bacteria which colonise mucosal surfaces and produce superantigenic toxins. One species implicated in recent studies of SIDS infants is Staphylococcus aureus. We tested the hypothesis that in comparison to infant formula, human milk might be a better inhibitor of binding of S. aureus to epithelial cells. In this study, two protocols were used for the binding assays which were assessed by flow cytometry: the in vitro method in which bacteria were treated with milk or formula, washed and added to epithelial cells; and a method more closely reflecting the competitive interactions in vivo in which cells, bacteria, and milk or infant formula were added at the same time. With the in vivo method, breast milk caused enhancement of bacterial binding to cells whilst infant formula caused inhibition; however, for the in vitro method, both human milk and infant formula caused consistent enhancement of binding. Flow cytometry and light microscopy studies indicated that the enhancement was due to the formation of bacterial aggregates. Human milk and infant formula preparations were also compared for components (antibodies or oligosaccharides) that could inhibit binding of S. aureus using the in vitro method. Human milk contained both IgA and IgG. Neither human milk nor infant formula contained oligosaccharides reactive with the Ulex europaeus lectin but both contained components that bound monoclonal antibodies to Lewis(a) and Lewis(b) antigens which can act as receptors for S. aureus. With both methods, synthetic Lewis(a) and Lewis(b) inhibited S. aureus binding in a dose-dependent manner. With human milk, however, the only component which showed a significant correlation with inhibition of binding was the IgA specific for the staphylococcal surface component that binds Lewis(a). Both human milk and infant formula contain components which could potentially inhibit bacterial binding but only breast milk contains the IgA specific for the bacterial adhesin that binds Lewis(a). Studies using the in vivo method suggest that protection associated with breast feeding in relation to SIDS could be due mainly to the formation of bacterial aggregates. The studies have implications for further research into constituents of infant formula.

Exposure to cigarette smoke, a major risk factor for sudden infant death syndrome: effects of cigarette smoke on inflammatory responses to viral infection and bacterial toxins

Exposure to cigarette smoke is a major risk factor for sudden infant death syndrome and also for respiratory infections in children. It has been suggested that toxigenic bacteria colonizing the respiratory tract might play a role in some cases of sudden infant death syndrome and nicotine has been demonstrated to enhance the lethality of bacterial toxins in a model system. Pyrogenic toxins of Staphylococcus aureus have been identified in tissues of infants who died of sudden infant death syndrome. It has been suggested that some of these deaths were due to induction of inflammatory mediators by infectious agents during a period when infants are less able to control these responses. The aim of this study was to assess the effects of a water-soluble cigarette smoke extract on the production of tumor necrosis factor alpha and nitric oxide from human monocytes in response to staphylococcal toxic shock syndrome toxin 1 or infection of the monocytes with respiratory syncytial virus. Cell culture supernatants were examined by a bioassay using mouse fibroblasts (L-929 cell line) for tumor necrosis factor alpha activity and by a spectrophotometric method for nitrite. Compared with monocytes incubated with medium only, monocytes incubated with any of the factors or their combinations tested in the study released higher levels of tumor necrosis factor alpha and lower levels of nitric oxide. Incubation with cigarette smoke extract increased tumor necrosis factor alpha from respiratory syncytial virus-infected cells while it decreased tumor necrosis factor alpha from cells incubated with toxic shock syndrome toxin. Incubation with cigarette smoke extract decreased the nitric oxide production from respiratory syncytial virus-infected cells while it increased the nitric oxide production from cells incubated with toxic shock syndrome toxin. Monocytes from a minority of individuals demonstrated extreme tumor necrosis factor alpha responses and/or very high or very low nitric oxide. The proportion of samples in which extreme responses with a very high tumor necrosis factor alpha and very low nitric oxide were detected was increased in the presence of the three agents to 20% compared with 0% observed with toxic shock syndrome toxin 1 or 4% observed with cigarette smoke extract or respiratory syncytial virus.

Sudden infant death syndrome, virus infections and cytokines

Many epidemiological risk factors identified for sudden infant death syndrome (SIDS) suggest a viral aetiology, e.g. exposure to cigarette smoke and winter peak, mild respiratory symptoms. Virus infections and bacterial toxins induce cytokine activity and it has been suggested that uncontrolled inflammatory mediators could be involved in some cases of SIDS. The aim of this review was to assess the evidence for virus infection in SIDS and to examine those findings in relation to individual variations in cytokine responses and various pathophysiological mechanisms proposed for SIDS such as sleep derangement, hypoxia, cardiac arrhythmia, vascular hypotonicity and hypoglycaemia.

Preliminary investigation of lethally toxic sera of sudden infant death syndrome victims and neutralisation by commercially available immunoglobulins and adult sera

The aim of the study was to test the hypotheses (i) that sudden infant death syndrome sera are toxic to 11-day old chick embryos and (ii) that such a toxicity can be counteracted by immunoglobulin or adult sera. Serum samples from 11 SIDS victims and five controls were tested for lethal toxicity in the chick embryo bioassay. Five serum samples were used to challenge chick embryos injected with the following: sudden infant death syndrome serum plus Hank's balanced salt solution; Hank's balanced salt solution alone; sudden infant death syndrome serum plus 3% w/v commercial immunoglobulin; sudden infant death syndrome serum plus 6% w/v immunoglobulin; sudden infant death syndrome serum plus pooled sera of 40 healthy adults. Results obtained revealed that Hank's balanced salt solution, the pooled adult serum and the commercial immunoglobulin were all non-lethal, in the chick embryo test system. By contrast. 10 sudden infant death syndrome victims yielded sera containing lethal levels of toxin(s) compared to 2/5 controls which was statistically significant (P < 0.05, Fischer's exact test). In the tests of sudden infant death syndrome serum plus immunoglobulin or pooled adult serum, the lethality of sudden infant death syndrome serum was abolished in all cases. The reduction in toxicity of individual sudden infant death syndrome serum plus immunoglobulin or pooled adult serum was often statistically significant (P<0.05-P<0.00005, Fischer's exact test). We conclude that lethal levels of toxin are present in sudden infant death syndrome sera and that they can be neutralised by normal immune serum. These results indicate that passive immunisation is a potential treatment to protect babies considered at risk from sudden infant death syndrome.

Cortisol levels and control of inflammatory responses to toxic shock syndrome toxin-1 (TSST-1): the prevalence of night-time deaths in sudden infant death syndrome (SIDS)

There is evidence that inflammatory responses have been induced in the tissues and body fluids of many SIDS infants. We suggested that some of these deaths are due to uncontrolled inflammatory responses to infectious agents and possibly cigarette smoke. The majority of SIDS deaths occur during the 2-4 month age range when infants have decreasing levels of maternal antibodies to infectious agents. Most deaths occur during the early hours of the morning. Adults are more susceptible to inflammatory responses at night due to lower levels of cortisol associated with circadian rhythm patterns. Infants develop these patterns between the ages of 7 weeks and 4 months, at which time their night-time cortisol levels drop dramatically. The objective of this study was to use an in vitro model system to assess the effects of different cortisol levels on proinflammatory cytokine production in response to the staphylococcal toxic shock syndrome toxin-1 (TSST-1) which has been identified in a significant number of SIDS infants. Levels of cortisol present in infants at night and during the day before and after the development of the circadian rhythm pattern were examined. Human buffy coats (n = 9) were stimulated with TSST-1 and responses assessed over 72 hours by a bioassay for tumour necrosis factor-alpha (TNF-alpha) and an enzyme linked immunosorbent assay (ELISA) for interleukin-6 (IL-6). Cortisol levels present in an infant at night after development of circadian rhythm (< or = 5 microg dl(-1)), did not significantly increase or decrease production of either TNF-alpha or IL-6. Concentrations of cortisol greater than 5 microg dl(-1) usually found in infants during the day or at night prior to the physiological change significantly decreased production of TNF-alpha at 12 hours and of IL-6 at 12 and 16 hours. Only cortisol levels greater than 5 microg dl(-1) significantly decreased production of the pro-inflammatory cytokines by human buffy coats stimulated with TSST-1. If the switch to the circadian rhythm pattern occurs in an infant when maternal antibodies are still present or after they have developed their own active immunity, the infant could neutralise common viruses, toxins or bacteria: however, if this switch occurs in an infant when antibody levels are low, this could be a window of vulnerability during which infants are at an increased risk of death if uncontrolled inflammatory responses are induced by infectious agents or their products.

Detection of pyrogenic toxins of Staphylococcus aureus in sudden infant death syndrome

It has been suggested that pyrogenic toxins of Staphylococcus aureus are involved in the series of events leading to some cases of sudden infant death syndrome (SIDS). The objectives of the study were to screen tissues from SIDS infants for pyrogenic toxins and to compare incidence of identification of these toxins among these infants from different countries. An enzyme-linked immunosorbent assay (ELISA) and a flow cytometry method were used to screen body fluids and frozen or formalin-fixed tissues for pyrogenic toxins of S. aureus, toxic shock syndrome toxin 1 (TSST), staphylococcal enterotoxins A (SEA), B (SEB), and C1 (SEC). Toxins were identified in tissues of 33/62 (53%) SIDS infants from three different countries: Scotland (10/ 19, 56%); France (7/13, 55%); Australia (16/30, 53%). In the Australian series, toxins were identified in only 3/19 (16%) non-SIDS deaths (chi2 = 5.42, P < 0.02). The flow cytometry method was useful for toxin detection in both frozen and fixed tissues, but ELISA was suitable only for frozen tissues or those fixed for less than 12 months. Identification of pyrogenic toxins in > 50% of SIDS infants from three different countries indicated further investigation into the role the toxins play in cot deaths might result in development of additional measures to reduce further the incidence of these infant deaths.

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

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 alpha (TNF-alpha) 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-alpha levels elicited by the toxins were not reduced by night time levels of cortisol (5-10 microg dl(-1)) levels. Day time levels of cortisol (10-20 microg dl(-1)) significantly inhibited IL-6 production but not TNF-alpha in responses. Stress levels of cortisol (40 80 microg 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-alpha 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-alpha 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.

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): III. Detection of IgA antibodies in human milk that bind to bacterial toxins implicated in SIDS

Two toxin-producing bacteria implicated in sudden infant death syndrome (SIDS) are Staphylococcus aureus and Clostridium perfringens. Epidemiological studies have shown that breast feeding reduces an infant's risk of SIDS. This protective effect could be due partly to IgA antibodies to these toxins in human milk. The aim of this work was to use a quantitative ELISA to determine levels of IgA antibodies that bound to toxic shock syndrome toxin (TSST-1), staphylococcal enterotoxin C (SEC) and C. perfringens enterotoxin A (CEA) in individual samples of human milk. All samples of milk tested contained IgA antibodies that bound to the bacterial toxins. For individual samples, IgA bound to TSST-1, SEC and CEA were in the range of 900-3100 ng ml(-1), 1000-3600 ng ml(-1) and 1000-4300 ng ml(-1) respectively. Isolation of S. aureus from mothers donating breast milk samples was used to determine if the presence of bacteria affected IgA levels which bound TSST-1 and SEC. For 3/5 samples with levels above the upper limit of the standard deviation (2375 ng ml(-1)) for IgA bound to TSST-1, S. aureus was isolated from the mother whilst 4/5 samples found to contain levels above the upper limit of the standard deviation (2627 ng ml(-1)) for IgA bound to SEC, had S. aureus isolated from the mother. In conclusion, if bacterial toxins do play a role in precipitating a SIDS death, the presence of IgA antibodies to toxins in breast milk, but not in infant formula, might contribute to the protective effect of breast feeding in relation to SIDS.

The protective effect of immunisation against diphtheria, pertussis and tetanus (DPT) in relation to sudden infant death syndrome

Epidemiological evidence indicates infants immunised against diphtheria, pertussis and tetanus (DPT) are at decreased risk of sudden infant death syndrome (SIDS). Asymptomatic whooping cough and pyrogenic toxins of Staphylococcus aureus have been implicated in the aetiology of SIDS. The objectives of the present study were: (1) to determine if the DPT vaccine induced antibodies cross-reactive with the staphylococcal toxins; (2) to determine if antibodies to the pertussis toxin (PT) and the staphylococcal toxins were present in the sera of women during late pregnancy; (3) to examine the effects of infant immunisation on levels of antibodies to PT and the staphylococcal toxins; (4) to assess the effects of changes in immunisation schedules in the UK on the incidence and age distribution of SIDS. Enzyme-linked immunosorbent assays (ELISA) were used to measure binding of rabbit or human IgG to the DPT vaccine, PT, toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxins A (SEA), B (SEB) and C (SEC). Neutralisation activity of anti-DPT serum was assessed by a bioassay for induction of nitric oxide from human monocytes by the staphylococcal toxins. Anti-DPT serum bound to the DPT vaccine, PT and each of the staphylococcal toxins. It also reduced the ability of the four toxins to induce nitric oxide from monocytes. In pregnant women, levels of IgG to PT, SEC and TSST-1 decreased significantly in relation to increasing weeks of gestation while antibodies to SEA and SEB increased. In infants' sera there were significant correlations between levels of IgG bound to DPT and IgG bound to PT, TSST-1 and SEC but not SEA or SEB. Antibody levels to the toxins in infants declined with age; sera from infants < or = 2 months of age had higher levels of IgG bound to the toxins than those older than 2 months. This pattern was observed for infants whose immunisation schedules began at 2 months of age or 3 months of age. The decrease in IgG bound to the toxins was, however, less for those immunised at 2 months. The decrease in SIDS deaths after the change in immunisation schedules was greatest in the 4-6-month age range. While DPT immunisation might prevent some unexplained infant deaths due to asymptomatic whooping cough, these data indicate that immunisation with DPT also induces antibodies cross-reactive with pyrogenic staphylococcal toxins implicated in many cases of SIDS. Passive immunisation of infants who have low levels of these antibodies might reduce further the numbers of these infant deaths.

IL-6 cerebrospinal fluid levels are related to laryngeal IgA and epithelial HLA-DR response in sudden infant death syndrome

The objective was to investigate whether there is any correlation between signs of central and peripheral immune stimulation in victims of sudden infant death syndrome (SIDS), the former expressed by IL-6 in cerebrospinal fluid (CSF), the latter by IgA, IgG, and IgM immunocytes, T lymphocytes, and HLA-DR expression in laryngeal mucosa. Seventeen SIDS cases with low CSF IL-6 levels (< or =5 pg/mL) and 20 cases with high CSF IL-6 levels (> or =30 pg/mL) were subjected to immunohistochemical quantitation of IgA, IgG, and IgM immunocytes; semiquantitative scoring of T lymphocytes in the mucosa of epiglottis and larynx, and semiquantitative evaluation of HLA-DR expression. SIDS cases with IL-6 levels > or =30 pg/mL had a significantly higher number of IgA immunocytes in laryngeal mucosa (p = 0.007) and in epiglottis (p = 0.03) than cases with IL-6 levels < or =5 pg/mL. Furthermore, laryngeal HLA-DR expression was significantly more extensive in SIDS cases with IL-6 levels > or =30 pg/mL than in those with levels < or =5 pg/mL (p = 0.05). No differences were found for IgG and IgM immunocytes or for T cells. In addition, babies found prone more often had symptoms of slight infection before death and had a higher number of IgA immunocytes in the larynx (p = 0.02) than babies sleeping on their side or back. Because IL-6 levels > or =30 pg/mL correspond to the levels found in infants who die from infectious diseases such as meningitis/septicemia and pneumonia, the findings favor the hypothesis that many SIDS cases may be caused by an "overreaction" of the immune system to an otherwise harmless infection.

Infection, inflammation and sleep: more pieces to the puzzle of sudden infant death syndrome (SIDS)

Risk factors for sudden infant death syndrome (SIDS) parallel those for respiratory tract infections; however, infectious agents suggested to be involved in SIDS do not fulfil Koch's postulates. No single agent has been identified in all cases and there is no suitable animal model for SIDS which could be used to test the candidate organisms. Based on epidemiological and experimental work by our group and others, we suggested some SIDS deaths are due to pathophysiological responses elicited by combinations of microbial products and/or cigarette smoke during a developmental stage when infants' endocrine responses are less able to "damp down" the effects of inflammatory mediators. Here we review evidence from studies on interactions between developmental and environmental risk factors that could affect 1) mucosal colonization of infants by potentially pathogenic bacteria, and 2) induction and control of infants', inflammatory responses to infectious agents. New evidence suggests that there are genetic factors involved in the induction of inflammatory responses to some bacterial antigens implicated in SIDS. Further investigation of the role of infection, exposure to cigarette smoke and inflammation in infants, particularly differences in ethnic groups at increased risk of SIDS, could lead to new insights into the events leading to a fatal outcome and perhaps to new intervention schemes to reduce further the incidence of these deaths.

Mannan binding lectin and the sudden infant death syndrome

Mannan binding lectin (MBL) may be important for innate immunity and some cases of sudden infant death syndrome (SIDS) may be preceded by bacterial infection. Therefore, relative MBL deficiency might be associated with susceptibility to SIDS. We measured MBL concentrations in 46 SIDS infants and 26 controls. The proportion of subjects with low MBL values was similar in the two groups. However, the mean for the SIDS group (3 micrograms/ml) was higher than that of the controls (2.2 micrograms/ml; P < 0.05). We interpret this difference as due to acute phase responses and suggest these findings are consistent with the view that some cot deaths are preceded by bacterial infections.

Bacterial toxins and sudden unexpected death in a young child

The sudden unexpected death of a six year old child following an upper respiratory tract infection is reported. Laboratory investigations revealed the presence of staphylococcal toxic shock syndrome toxin-1 (TSST-1) in samples of brain tissue. The significance of this finding is discussed.

Is the nasopharynx warmer in children than in adults?

Recent studies on the aetiology of the Sudden Infant Death Syndrome (SIDS) have suggested that some of these deaths are the consequence of an overwhelming inflammatory response to the production of pyrogenic toxins from bacteria colonizing the upper respiratory tract, particularly the nasopharynx. The pyrogenic toxins of Staphlococcus aureus, one of the likelier bacterial candidates, are only produced in temperatures of over 37 degrees C. This study examined nasopharyngeal temperatures in children. It is a preliminary study to develop an accurate means to measure how close to 37 degrees C the nasopharyngeal temperature lies in infants at the age when SIDS deaths occur. Following a pilot study and power calculation, measurements of nasopharyngeal temperature were made on 30 apyrexial children aged 4-10 years and 30 adults with no nasal pathology, undergoing surgery under general anaesthesia, using an accurately sited thermocouple probe. The mean temperature in children (35.64 degrees C) was significantly higher than in adults (34.01 degrees C). Comparable measurements attempted with the same subjects awake gave similar results.

Developmental and environmental factors that enhance binding of Bordetella pertussis to human epithelial cells in relation to sudden infant death syndrome (SIDS)

Asymptomatic infection due to Bordetella pertussis has been suggested to be one cause of sudden infant death syndrome (SIDS). We examined developmental and environmental factors previously found to affect binding of another toxigenic species, Staphylococcus aureus, to human epithelial cells: expression of the Lewis(a) antigen; infection with respiratory syncytial virus (RSV); exposure to cigarette smoke; and the inhibitory effect of breast milk on bacterial binding. Binding of two strains of B. pertussis (8002 and 250825) to buccal epithelial cells was significantly reduced by treating the cells with monoclonal antibodies to Lewis(a) (P < 0.05) and Lewis(x) (P < 0.01) antigens. Both strains bound in significantly greater numbers to cells from smokers compared with cells from non-smokers (P < 0.05). HEp-2 cells infected with RSV subtypes A or B had higher binding indices for both 8002 (P < 0.001) and 250825 (P < 0.01). On RSV-infected cells, there was significantly enhanced binding of monoclonal antibodies to Lewis(x) (P < 0.05), CD14 (P < 0.001) and CD18 (P < 0.01); and pre-treatment of cells with anti-CD14 or CD18 also significantly reduced binding of both strains of B. pertussis. Pre-treatment of the bacteria with human milk significantly reduced their binding to epithelial cells. The results are discussed in relation to our three-year survey of bacterial carriage among 253 healthy infants, their mothers and local SIDS cases between 1993-1995 and in relation to the change to an earlier immunisation schedule for infants and the recent decline in SIDS in Britain.

Clostridium perfringens type A enterotoxin (CPE): more than just explosive diarrhea

The bacterial pathogen Clostridium perfringens is the most prolific toxin-producing species within the clostridial group. The toxins are responsible for a wide variety of human and veterinary diseases, many of which are lethal. C. perfringens type A strains are also associated with one of the most common forms of food-borne illness (FBI). The toxicosis results from the production and gastrointestinal absorption of a protein-enterotoxin known as CPE. The regulation, expression, and mechanism of action of CPE has been of considerable interest as the protein is unique. CPE expression is sporulation associated, although the mechanism of cpe-gene regulation is not fully elucidated. Cloning studies suggest the involvement of global regulators, but these have not been identified. Although very few type A strains are naturally enterotoxigenic, the cpe gene appears highly conserved. In FBI strains, cpe is chromosomally encoded; whereas in veterinary strains, cpe may be plasmid-encoded. Variation in cpe location suggests the involvement of transposable genetic element(s). CPE-like proteins are produced by some C. perfringens types C and D; and silent remnants of the cpe gene can be found in C. perfringens type E strains associated with the iota toxin gene. CPE has received attention for its biomedical importance. The toxin has been implicated in sudden infant death syndrome (SIDS) because of its superantigenic nature. CPE can destroy a wide variety of cell types both in vitro and in vivo, suggesting that it could have potential in the construction of immunotoxins to neoplastic cells. It is obvious that CPE is an interesting protein that deserves continued attention.