Lung immunoglobulins in the sudden infant death syndrome

Pulmonary immune profiling of SIDS: impaired immune maturation and age-related cytokine imbalance

BACKGROUND

For sudden infant death syndrome (SIDS), an impaired immunocompetence has been discussed for a long time. Cytokines and chemokines are soluble immune mediators (SIM) whose balance is essential for the immune status. We hypothesized that an imbalanced immune response might contribute to the etiology of SIDS.

METHODS

We investigated 27 cytokines, chemokines, and growth factors in protein lysates of lungs derived from 29 SIDS cases and 15 control children deceased for other reasons.

RESULTS

Except for the CCL5, no significant differences were detected in the lungs between SIDS cases with and without mild upper respiratory tract infections. In contrast, IL-1RA, IL-7, IL-13, and G-CSF were decreased in the merged SIDS cases compared to control cases without evidence of infection. Plotting SIM concentrations against infant age resulted in increasing concentrations in control but not in SIDS lungs, indicating a disturbed immune maturation. Moreover, an age-dependent shift towards a Th2-related pattern was observed in SIDS.

CONCLUSIONS

Our findings suggest that an impaired maturation of the immune system, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in triggering SIDS. These findings might in part be explained by chronic stress.

IMPACT

Maturation of the cytokine and chemokine network may be impaired in SIDS. An imbalance between Th1- and Th2-related cytokines, which may reflect a state of chronic stress causing a more Th2 shift. An impaired immune maturation, an insufficient response to respiratory pathogens, and an immune response modulated by Th1/Th2 imbalance might play a possible role in SIDS.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Response of smooth bronchial musculature in bronchoconstrictor substances in newborn with lung atelectasis at the respiratory distress syndrome (RDS)

Objective:

Role of the atelectasis (hypoxia) in the respiratory system of the live and exited newborn (250 up to 3000 g. of body weight), which has died due to different causes was studied in this work.

Methods:

Response of tracheal rings to dopamine, serotonine and ethanol in the different molar concentrations (dopamine: 0,05 mg/ml, 0,5 mg/ml, 5 mg/ml; serotonine (5-HT): 10^-4, 10^-3, 10^-2, 10^-1 mol/dm³; ethanol: 0,2 ml, 0,5 ml, 1,0 ml; 96%) was followed up. Study of the smooth tracheal musculature tone (STM) was elaborated in 16 tracheal preparations taken following the newborn death due to different causes.

Results:

Based on functional researches of tracheal isolated preparations, it was ascertained as follows: atelectasis (cases born with lung hypoxia) has changed the response of STM to dopamine, serotonine and ethanol in a significant manner (p<0,01) in comparison to cases of controlling group, which has died due to lung inflammatory processes (e.g. pneumonia, bronchopneumonia, cerebral hemorrhage), which have also caused significant response (p<0,05).

Conclusion:

Results suggest that exited cases from lung atelectasis and cases of controlling group reacts to above mentioned substances by causing significant constrictor action of tracheobronchial system.

IL-1 gene cluster polymorphisms and sudden infant death syndrome

Several studies indicate that interleukin gene polymorphisms are of importance to sudden infant death syndrome (SIDS), and so far it has been reported that associations between SIDS and polymorphism in the genes encoding tumor necrosis factor alpha, IL (interleukin)-6, and IL-10. IL-1 are important for the synthesis of acute phase proteins, and it is a pyrogen cytokine that may cause fever. The purpose of the present study was to investigate two polymorphisms in the IL-1alpha gene; a variable number of tandem repeat (VNTR) in intron 6 and a single nucleotide polymorphism in +4845G/T, as well as the -511C/T polymorphism in the gene encoding IL-1beta, and a VNTR in intron 2 of the competitive antagonist IL-1Ra, in SIDS cases, cases of infectious death, and controls. Furthermore, the genotypes were correlated with known external risk factors for SIDS. When investigating each polymorphism separately, no differences in genotype distribution between the diagnosis groups and controls were found. However, when combining VNTR and single nucleotide polymorphism genotypes, an association between the gene combination IL-1alpha VNTR A1A1/IL-1beta+ +4845TT and SIDS was disclosed (p < 0.01). In the SIDS group it was also found that the genotypes IL-1beta -511CC/CT were significantly more frequent in the SIDS victims found dead in a prone sleeping position, compared with SIDS victims found dead in other sleeping positions (p = 0.004). The findings in the present study indicate that specific interleukin gene variants may be a predisposing factor for sudden unexpected infant death.

Postnatal hypokinesia and the delayed time frame of sudden infant death syndrome

The sudden infant death syndrome peaks in the second and third month of life. This is the period of the "two-month transformation of the central nervous system" in the human infant. Studies of 120 days of imposed hypokinesia in man demonstrated that the maximum period of autonomic dysfunction was delayed until the beginning of the second month through to the fourth month of the experiment. Hypokinesia also impaired sleep mechanisms and induced polymorphic changes in almost all systems of the human body. These studies suggest that prolonged postnatal hypokinesia in infants may induce autonomic dysfunction in the CNS, especially during the "two-month transformation period" of major postnatal neural development.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Sudden infant death syndrome, infection and inflammatory responses

Sudden infant death syndrome (SIDS) is sudden unexpected death in infancy for which there is no explanation after review of the history, a death scene investigation and a thorough autopsy. The use of common diagnostic criteria is a prerequisite for discussing the importance of infection, inflammatory responses and trigger mechanism in SIDS. Several observations of immune stimulation in the periphery and of interleukin-6 elevation in the cerebrospinal fluid of SIDS victims explain how infections can play a role in precipitating these deaths. Finally, these findings and important risk factors for SIDS are integrated in the concept of a vicious circle for understanding the death mechanism. The vicious circle is a concept to elucidate the interactions between unfavourable factors, including deficient auto-resuscitation, and how this could result in death.

Mucosal immune responses to infections in infants with acute life threatening events classified as 'near-miss' sudden infant death syndrome

This study examined the hypothesis that dysregulation of mucosal immune responses to respiratory infections is a critical event, which could be causal in respiratory arrest of some previously healthy infants. To examine this hypothesis, a prospective study was undertaken of infants presenting to the emergency department of a major teaching hospital with acute life threatening events (ALTE) of unknown cause and classified as "near-miss" SIDS. Salivary immunoglobulin concentrations were measured on admission and again after 14 days. The salivary immunoglobulins were compared with three control groups: infants with a mild upper respiratory tract infection (URTI); bronchiolitis; and healthy age-matched infants. The salivary IgA and IgM concentrations in the ALTE infants at presentation to hospital indicated a significant mucosal immune response had already occurred, with nearly 60% of the IgA concentrations significantly above the population-based reference ranges. The hyper-immune response was most evident in the ALTE infants with pathology evidence of an infection; 87% of these infants had salivary IgA concentrations on average 10 times higher that the age-related median concentration. The most prevalent pathogen identified in the ALTE infants was respiratory syncytial virus (RSV) (64%). RSV was also identified in all subjects with bronchiolitis. Risk factors for SIDS were assessed in each group. The data indicated that the ALTE infants diagnosed as 'near-miss' SIDS were a relatively homogeneous group, and most likely these ALTE infants and SIDS represent associated clinical outcomes. The study identified exposure to cigarette smoke and elevated salivary IgA concentrations as predictors of an ALTE. The study findings support the hypothesis of mucosal immune dysregulation in response to a respiratory infection in some infants with an ALTE. They provide a plausible explanation for certain SIDS risk factors. The underlying patho-physiological mechanism of proinflammatory responses to infections during a critical developmental period might be a critical factor in infants who have life-threatening apnoea or succumb to SIDS. The study raises the possibility of using salivary IgA to test infants who present with mild respiratory infections to identify a substantial number of infants at risk of developing an ALTE or SIDS, thus enabling intervention management to prevent such outcomes.

Development of mucosal immunity in the first year of life and relationship to sudden infant death syndrome

The common mucosal immune system (CMIS) is an interconnecting network of immune structures that provides effective immunity to mucosal surfaces. The structures of the mucosal immune system are fully developed in utero by 28 weeks gestation, but in the absence of intrauterine infection, activation does not occur until after birth. Mucosal immune responses occur rapidly in the first weeks of life in response to extensive antigenic exposure. Maturation of the mucosal immune system and establishment of protective immunity varies between individuals but is usually fully developed in the first year of life, irrespective of gestational age at birth. In addition to exposure to pathogenic and commensal bacteria, the major modifier of the developmental patterns in the neonatal period is infant feeding practices. A period of heightened immune responses occurs during the maturation process, particularly between 1 and 6 months, which coincides with the age range during which most cases of sudden infant death syndrome (SIDS) occur. A hyper-immune mucosal response has been a common finding in infants whose death is classified as SIDS, particularly if in association with a prior upper respiratory infection. Inappropriate mucosal immune responses to an otherwise innocuous common antigen and the resulting inflammatory processes have been proposed as factors contributing to SIDS.

Apnea and bradycardia due to anaphylaxis to tobacco glycoprotein in the infant rabbit

Prenatal and postnatal exposure to cigarette smoke is associated with an increased incidence of the sudden infant death syndrome, although the cause(s) for this is unknown. Tobacco glycoprotein (TGP), a group of proteins purified from cured tobacco leaves and present in cigarette smoke, have been shown to cause anaphylaxis in excised hearts and lungs of adult rabbits that were neonatally sensitized to TGP and later rechallenged. We sought to determine whether anaphylaxis occurred in live infant rabbits who were neonatally sensitized to TGP. At the age of 1 day, 12 animals were sensitized to TGP (0.1mg in 0.25 cc alum) via intraperitoneal injection (i.p.i.) followed by a booster ipi at the age of 30 days (TGP-S). Seven animals received i.p.i. of antigen-free alum only (controls). All animals underwent an intravenous TGP challenge at age 42+/-2 days. Heart rate (HR) and respiratory rate (RR) were recorded for 2 min prior to and 5 min after the challenge. Baseline HR (approximately 260) and RR (approximately 120) were similar in all animals. Seven TGP-S animals developed apnea (1.9-4.7s) within 60s of the challenge while none of the controls did. The TGP-S also became bradycardic (the lowest HR over 50 consecutive beats), with the HR decreasing from 260 to 220 vs the controls, whose HR remained constant (approximately 250). We conclude that some rabbits neonatally sensitized to TGP develop apnea and bradycardia upon further intravenous TGP challenge. These studies suggest that cigarette smoke exposure may be associated with a higher rate of SIDS via an anaphylactic mechanism.

Sudden infant death syndrome and enteric infection

The association of Helicobacter pylori in the stomach, trachea and lungs with the incidence of SIDS, gastric ulcers and cancer may have a counterpart in animals. In field studies of white muscle disease (WMD) and hepatic necrosis in selenium-deficient pigs dying suddenly, veterinarians identified gastric ulcers in 40% of inspected piglets. The lesion was also commonly observed by researchers in experimentally produced vitamin E-selenium deficiency and other researchers suspected that gastric ulcers in swine may be associated with vitamin E-selenium deficiency. Mice preferentially concentrated (75)selenium in peritoneal exudative cells (PEC) when (75)selenium as selenium selenate was administered by stomach tube to selenium-deficient mice. Selenium concentrated in PECs as glutathione peroxidase (GSHP(x)). GSHP(x)-deficient leucocytes in peritoneal exudate failed to kill yeast cells. GSHP(x) deficiency has also been associated with decreased microbicidal activity of leucocytes in patients with chronic granulomatosis. The selenium-deficient swine were usually growing rapidly in crowded conditions, and, apart from WMD and hepatic necrosis, edema was prominent in the spiral colon, subcutaneous tissues, lungs and submucosa of the stomach. The elevated immunological response in the spleen and lungs of SIDS victims suggests an initial defective microbicidal propensity of the peritoneal exudative cells.

Sudden infant death syndrome Part 2: the response of the reticuloendothelial system to hypoxemia and infection

The incidence of ascites in chicks raised in a high-altitude chamber doubled from 6500 feet to 8000 feet. A similar condition developed in calves transported to pasture at high altitude. Chicks raised in a high-altitude chamber (compared to controls) produced more plasma cells in the germinal centres of the spleen about four days after an antigen challenge. Children usually suffering from a mild respiratory infection at sea level often developed pulmonary edema (HAPE) on transfer to high altitude. Sudden infant death syndrome (SIDS) victims produced more plasma cells in the germinal centers of the spleen. In one survey of SIDS, about half of the infants suffered an upper respiratory tract infection in the two weeks prior to death and the lungs were filled with fluid at autopsy. Elevated levels of hypoxanthine indicated hypoxemia before death, and a presumed response to hypoxemia in SIDS was the presence of extramedullary hematopoiesis in the liver. The effect of prolonged hypoxemia and infection are additive in increasing vascular permeability and the accumulation of edema fluid. The preferential uptake of zinc by edema fluid proteins at the expense of inflammatory cells increases the motility and metabolism of zinc-deprived activated macrophages. Activated macrophages release cytokines which in turn stimulate the release of pro-inflammatory peptides which increase vascular permeability and mortality. These inflammatory peptides are under proteolytic control. The neutral endopeptidase (NEP) is a cell-surface zinc metalloproteinase which modulates toxic shock.Zinc also modulates the inflammatory response of the activated macrophage. Interleukin-12 (IL-12), predominantly a product of macrophages, is involved in regulating both hematopoiesis and the adaptive immune response. IL-12 promotes interferon gamma (IFNgamma) production by T cells. IFNgamma acts on macrophages to release large amounts of nitric oxide (NO). An elevated immune response leads to NO overload, dilation of the cardiovascular system and toxic shock. A mechanism resulting in cardiovascular failure and a shock-like sequence is described in some cases of SIDS.Bradycardia, recorded on cardiorespiratory monitors in six SIDS infants, was considered a late event. Cytokines regulate all aspects of the immune response. Extramedullary hematopoiesis in the liver was one anatomical marker of hypoxemia in SIDS. This survey traces the function of the activated macrophage with the cytokines regulating extramedullary hematopoiesis and the precocious immune response in SIDS.

Review of risk factors for sudden infant death syndrome

Sudden infant death syndrome (SIDS) accounts for the largest number of deaths during the first year of life in developed countries. The possible causes of SIDS are numerous and, to date, there is no adequate unifying pathological explanation for SIDS. Epidemiological studies have played a key role in identifying risk factors, knowledge of which has underpinned successful preventive programmes. This review critically assesses information on the main risk factors and causal hypotheses put forward for SIDS, focusing on research published since 1994. The overall picture that emerges from this review is that affected infants are not completely normal in development, but possess some inherent weakness, which may only become obvious when the infant is subjected to stress. Initially there may be some minor impairment or delay in development of respiratory, cardiovascular or neuromuscular function. None of these is likely to be sufficient, in isolation, to cause death and, provided the infant survives the first year of life, may no longer be of any significance. However, when a compromised infant is confronted with one or more stressful situations, several of which are now clearly identified as risk factors, and from which the majority of infants would normally escape, the combination may prove fatal.

Sudden infant death syndrome (SIDS): T-cell immunodeficiency--Part 1

It is hypothesized that SIDS mimics AIDS and atopic eczema in that defective T lymphocytes and overactive B cells overstimulate pro-inflammatory cytokines in the mucosal immune system. Virally infected cells are unable to convert linoleic acid (LA) into gamma-linolenic acid (GLA) which eventually leads to defective T lymphocyte production. Abnormal lung cytokine synthesis by virus-induced immunodeficient T lymphocytes is associated with the murine AIDS-related complex (ARC). Adenosine triphosphate (ATP) deficient anaerobic cells cannot convert LA to GLA. It is hypothesized that, in SIDS victims, elevated levels of hypoxanthine and immunoglobulins are evidence of chronic hypoxemia and ATP catabolism, and an inability to convert LA to GLA, leading to defective T lymphocytes in the mucosal immune system.

The black infant's susceptibility to sudden infant death syndrome and respiratory infection in late infancy

Between 2 and 11 months of age, the risk of sudden infant death syndrome (SIDS) declines more slowly in black infants than in infants of other races. This phenomenon might also be a feature of certain non-SIDS causes of death. Identifying these causes may through analogy provide support for the theory that SIDS is a disease of the central nervous system, an unusual consequence of respiratory infection, or a form of suffocation. We used logistic regression analysis on details of infant deaths in the United States, 1985-1991, to examine the difference between the rates of decline with increasing age in the mortality rates of black infants and infants of other races. We defined slower rate of decline in black infants as a positive difference. The magnitude and direction (positive) of the difference for deaths due to respiratory infection were similar to those for SIDS. It is unlikely that this difference in the rates of decline for respiratory infection can be explained by diagnostic cross-misclassification between respiratory infection and SIDS. SIDS appears to be a disease of the respiratory system caused by infection that affects that system's control centers.

An association between sudden infant death syndrome (SIDS) and Helicobacter pylori infection

BACKGROUND

Helicobacter pylori has recently been detected in the stomach and trachea of cases of sudden infant death syndrome (SIDS) and proposed as a cause of SIDS.

AIMS

To establish the incidence of H pylori in the stomach, trachea, and lung of cases of SIDS and controls.

METHODS

Stomach, trachea, and lung tissues from 32 cases of SIDS and eight control cases were examined retrospectively. Diagnosis of SIDS was based on established criteria. Controls were defined by death within 1 year of age and an identifiable cause of death. Tissues were examined histologically for the presence of bacteria. Extracted DNA from these tissues was tested for H pylori ureC and cagA sequences by nested polymerase chain reaction and amplicons detected by enzyme linked immunosorbent assay (ELISA). The cut off for each ELISA for each of the tissue types was taken as the mean optical density plus two times the standard deviation of a range of negative controls.

RESULTS

Ages of SIDS cases ranged from 2 to 28 weeks. Ages of controls ranged from 3 to 44 weeks. For the ureC gene, 25 SIDS cases were positive in one or more tissues compared with one of the controls. For the cagA gene, 25 SIDS cases were positive in one or more tissues compared with one of the controls.

CONCLUSIONS

There is a highly significant association between H pylori ureC and cagA genes in the stomach, trachea, and lung of cases of SIDS when compared with controls.

Sudden infant death syndrome: a toxic response

Causes of sudden infant death syndrome (SIDS) remain elusive. Much of the current literature points to an infectious cause with a role for proinflammatory cytokines and septic shock in stimulating an overwhelming response in an infant. This article reviews the literature and possible causes of this devastating condition.

Association of sudden infant death syndrome with grossly deranged iron metabolism and nitric oxide overload

Sudden infant death syndrome (SIDS) occurs silently usually during sleep and, though remaining unexplained after autopsy, leaves footprints creating a pattern analogous to that which follows a flood of nitric acid (NO). These footprints in SIDS are associated with serious pathological changes, viz. elevated hepatic iron, bone marrow hyperplasia, hypomyelinated respiratory control centres, elevated lung immunoglobulins, cerebral hypoperfusion resembling lesions induced by chronic hypoxemia, ischemia, congenital heart disease and congenital myopathy. Hypoxia stimulates the immune response and the over-arousal of the immune response triggers a flood of NO. Adenosine triggers sleep. NO and adenosine are additive as dilators of coronary blood vessels. Blood pressure collapses. Selenium increases the activity of the enzyme ferrochelatase during incorporation of heme into cytochrome oxidase. NO binds to cytochrome oxidase, inhibiting respiration. When NO reaches dangerous levels, the cell turns on production of heme oxygenase. Heme is broken down to iron (Fe) carbon monoxide (CO) and bile pigments. NO has a huge affinity for hemoglobin which catalyses NO degradation to nitrate. Furthermore, NO is a product of smoke and SIDS incidence is higher in smoking mothers.

Sudden infant death syndrome: hypothalamic failure to sense elevated blood pyrogens

Sudden infant death syndrome (SIDS) is frequently associated with a mild infection, the incidence peaking during the third month of life. We hypothesize that the neonatal immaturity of both the acute febrile response and hypothalamus promote neonatal protection from SIDS. Vagal afferents modify the febrile response. Vagotomized rodents displayed a loss of febrile responsiveness in a 'non-sensing' brain. The failure of a 'non- sensing' brain to react to elevated blood pyrogens leads to failure of the febrile response and to a shock-like state. SIDS infants may appear well yet, within hours of this observation, may be found dead. There is a mismatch between the acute febrile response and hypothalamic hypoactivation. The discrepancy increase wtih development. There is an elevated cytokine response in endothelial cells which induces nitric oxide (NO) production and retarded development of the hypothalamus. Cigarette smoke also induces NO production and retards hypothalamic development by augmented apoptosis. Zinc inhibits this effect in mouse thymocytes. Fetal haemoglobin (HbF) induces hypoxia which is a stimulator of the immune response, while vasodilator gases (carbon monoxide (CO), NO) reduce hypothalamic function. The hypothalamic failure to sense elevated blood pyrogens induces toxic shock--a feature of SIDS.

Increased mast cell tryptase in sudden infant death - anaphylaxis, hypoxia or artefact?

BACKGROUND

Increased concentrations of mast cell tryptase in post mortem blood have frequently been observed in sudden infant deaths but the cause of this has not yet been clarified.

OBJECTIVE

The aim was to evaluate factors (immunological, morphological and anamnestic data) behind the observed increase in mast cell tryptase in sudden infant deaths with elevated tryptase.

METHODS

Mast cell tryptase and total immunoglobulin (Ig) E were measured in post mortem sera from 44 infants younger than 1.5 years. Radioallergosorbent tests were performed for possible allergens (mixture for relevant food allergens, Phadiatop and latex). IgG subclasses, IgM, and complement factors (C3, C4 and factor B) were measured with radial immunodiffusion. Mast cells, labelled with antibodies against mast cell tryptase, were counted in the lungs and heart. The circumstances of death and medical history of the deceased infant and family were obtained through police and hospital records.

RESULTS

In 40% of the SIDS cases tryptase was elevated (>10 microg/L). Total IgE in serum was increased in 33% compared with clinical reference values but showed no association with mast cell tryptase. RAST tests were positive in three cases. In one of these cases both tryptase and total IgE were elevated. The only variable that was associated with high tryptase values was prone position at death (P < or = 0.05 ). Allergy or asthma in the family were alleged in 50% of the cases, but was not associated with elevated tryptase or IgE. Children with elevated total IgE also displayed high concentrations of IgG1 and IgG2. Infants who died in the spring had significantly higher IgE than the others (P < or = 0.05).

CONCLUSION

The results do not support the hypothesis that the elevated tryptase concentrations in sudden infant death are caused by allergy. The association between prone position at death and elevated tryptase could hypothetically be explained by mast cell degranulation due to, for example, a hypoxic stimulus in these infants.

Immune and inflammatory responses in sudden infant death syndrome

Infancy is a time of unparalleled infection exposure. Coming from the privilege of the uterus, the newborn infant must make appropriate immune responses following infection that eliminates the infection but protects the host. There is evidence that in sudden infant death syndrome (SIDS) subjects there is a background of recent 'trivial' infection and immunological/inflammatory reactivity. This immunological/inflammatory reactivity is seen in enhanced pulmonary immunoglobulins and T-cell activation. It may be that in certain SIDS cases a trivial infection triggers an exaggerated inflammatory response, inducing cytokine cascades and eventual demise of the infant.

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.

Respiratory control during upper airway infection mechanism for prolonged reflex apnoea and sudden infant death with special reference to infant sleep position

The mortality rate of sudden infant death syndrome (SIDS) has been dramatically reduced after the supine sleeping position was recommended by health authorities. Concomitant with the decline in overall mortality rate, a marked attenuation of the seasonal distribution has been observed. So far, neither a satisfactory explanation of the previously noted seasonal variation, nor a generally accepted explanation for the preventive effect of supine sleeping position has been presented. Conceivably either the effect of some yet unidentified risk factor for sudden unexpected death in infancy was more prevalent during the dark and cold months of the year during the period when infants generally slept prone, or the effect of the risk factor(s) was more potent in the prone sleeping infant. Prolonged apnoea in infancy may lead to hypoxia, bradycardia and circulatory collapse. Reflex apnoea can be elicited by stimulation of chemoreceptors in the upper airway. The cardio-respiratory response to receptor stimulation is reinforced during a respiratory tract infection. Based on our own and others' experimental data, it is suggested that the reduction in sudden infant mortality rate and in particular the attenuation of the seasonal variation is in part an effect of the reduced likelihood of laryngeal chemoreceptors being stimulated by stagnated airway secretions during upper airway tract infection in the supine sleeping infant.

Sudden infant death syndrome: hypothalamic failure to sense elevated blood pyrogens

Sudden infant death syndrome (SIDS) is frequently associated with a mild infection, the incidence peaking during the third month of life. We hypothesize that the neonatal immaturity of both the acute febrile response and hypothalamus promote neonatal protection from SIDS. Vagal afferents modify the febrile response. Vagotomized rodents displayed a loss of febrile responsiveness in a 'non-sensing' brain. The failure of a 'non-sensing' brain to react to elevated blood pyrogens leads to failure of the febrile response and to a shock-like state. SIDS infants may appear well yet, within hours of this observation, may be found dead. There is a mismatch between the acute febrile response and hypothalamic hypoactivation. The discrepancy increases with development. There is an elevated cytokine response in endothelial cells which induces nitric oxide (NO) production and retarded development of the hypothalamus. Cigarette smoke also induces NO production and retards hypothalamic development by augmented apoptosis. Zinc inhibits this effect in mouse thymocytes. Fetal haemoglobin (HbF) induces hypoxia, which is a stimulator of the immune response while vasodilator gases (carbon monoxide (CO), NO) reduce hypothalamic function. The hypothalamic failure to sense elevated blood pyrogens induces toxic shock - a feature of SIDS.

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.

SIDS--changes in the epidemiological pattern in eastern Norway 1984-1996

The objective was to analyse differences in the epidemiological pattern of sudden death in infancy during two time periods--the Sudden Infant Death Syndrome (SIDS) 'epidemic': 1984-1989, and the period of rapid decline in the SIDS rate 1990-1996. Sex distribution, age, sleeping position, signs of infection, day of the week and place of death were registered and compared for the two time periods studied in all SIDS cases autopsied at the Institute of Forensic Medicine, Oslo. There were significantly more deaths in the age group under four months in the period 1984-89 than in the second period. Prone sleeping position, signs of infection, death outdoors and during the winter were more frequent during the first period than in the second. These features also were more frequent in the age group under four months than in the older babies during the first period. The shift in the epidemiological pattern after 1990, when the risk factor campaign was launched, indicates that prone sleeping position, cold climate, sleeping outdoors and infections seem to be risk factors that are particularly harmful to the youngest infants.

Proposed link between Helicobacter pylori and sudden infant death syndrome

Helicobacter pylori may be linked to sudden infant death syndrome (SIDS) through synthesis of inflammatory cytokines, particularly interleukin-1, which can produce fever, activation of the immune system, and increased deep sleep. A relatively minor respiratory or enteric infection, together with overwrapping and prone sleep position could then induce terminal hypoxemia. Alternatively, H. pylori produces large amounts of urease which, if aspirated in gastric juice, could reach the alveolae, react with plasma urea, and produce ammonia toxicity leading to respiratory arrest. Epidemiological similarities between H. pylori and SIDS are presented along with possible transmission mechanisms for H. pylori which support this hypothesis.

Immunoglobulin and beta 2-microglobulin concentrations in bronchoalveolar lavage of children and adults

Immunoglobulins play an important role in the pulmonary host defense, but little information is available about immunoglobulin and beta 2-microglobulin concentrations in the lung of normal children. Using bronchoalveolar lavage (BAL) we have studied immunoglobulin and beta 2-microglobulin levels in 30 children 3-15 years old undergoing elective surgery for nonpulmonary illnesses and in 15 healthy adult volunteers. BAL was performed with 3 x 1 ml/kg of body weight normal saline through an endotracheal tube after induction of anesthesia in children and under local anesthesia in adults. Similar concentrations of IgA and IgG were found in BAL fluid of children and adults even though serum levels were lower in children. As comparable results were obtained for albumin, a serum-derived protein, these data suggest that the permeability of the alveolar membrane is higher in children. IgE and IgM were detected in BAL fluid in only a fraction of children. beta 2-microglobulin levels were higher in both blood and BAL fluid of children. These data provide the first reference data for immunoglobulin and beta 2-microglobulin in children and can serve as a basis for future studies of children with pulmonary diseases.

Reflex apnoea response and inflammatory mediators in infants with respiratory tract infection

The reflex apnoea response to water stimulation was evaluated in infants with respiratory syncytial virus (RSV) infection and compared to the response in non-infected infants who had sustained an apparent life-threatening event (ALTE) or were siblings of infants who had died of sudden infant death syndrome (SIDS). RSV-infected infants had a significantly (p < 0.05) reinforced reflex apnoea response compared with non-infected infants. There was a significant negative correlation between the concentration of interleukin 1 beta (IL-I beta) in pharyngeal secretions and the duration of apnoea (p < 0.01). Increased clinical severity was, however, associated with high (> 5.000 pg ml-1) concentrations of IL-1 beta. There was no correlation between apnoea and interleukin 6. These findings may be relevant for the understanding of why apnoea may be the presenting symptom of RSV infection, and offer an explanation of why a proportion of SIDS cases has a history of mild respiratory tract symptoms prior to death.

Pulmonary eosinophilia in sudden infant death syndrome

A recent immunohistochemical study found increased numbers of eosinophils, but no mast cells, in the pulmonary parenchyma of infants who died of sudden infant death syndrome (SIDS). The present study tested the hypothesis that this pulmonary eosinophilia could be IgE-mediated. Histomorphometry was used to compare the numbers of eosinophils, mast cells, and IgG-, IgA-, IgM- and IgE-expressing lymphoid cells in the lungs of two groups of infants. Twenty-eight subjects aged less than 1 year were selected from post-mortem records of infant deaths between 1989 and 1992. Fourteen were cases of SIDS and these infants were matched for age and gender to 14 controls who died of other non-pulmonary conditions. Immunohistochemical stains were used and positive cells were counted on six peribronchial and six subpleural fields. The numbers of eosinophils in both peribronchial and subpleural regions were significantly higher in SIDS compared with controls (P = 0.0071 and P = 0.041, respectively). The numbers of IgA-expressing lymphoid cells were also significantly increased in SIDS cases (P = 0.042). There were no differences in IgG, IgM or IgE expression or in mast cell numbers. These results confirmed that pulmonary eosinophils are increased in SIDS, but not through an IgE-mediated pathway.

Sudden infant death syndrome and superoxide/nitric oxide

In a sudden infant death syndrome review Valdès-Dapena describes Naeye's report of increased medial muscle mass in walls of small pulmonary arteries and increased weight of cardiac right ventricles. These findings point to cardiorespiratory insufficiency, a problem in fast growing chicks raised at high altitudes. The vascular epithelium lining all blood vessels synthesises nitric oxide which induces relaxation of smooth muscle in vessel walls, and is possibly an important neurotransmitter. Others demonstrate that nitric oxide is involved in regulating vessel calibre, blood pressure and blood flow, as well as falls in ventricular outputs. Superoxide interacts with nitric oxide and removes it from the circulation. Superoxide is thus a vasoconstrictor. Superoxide is produced by activated phagocytes and possibly lymphocytes and other cell types in the immune response. Elevated immunoglobulins in mucus secretions are a hallmark in sudden infant death syndrome and hypoxic chicks. Our approach therefore is that cardiorespiratory insufficiency may be induced by superoxide in small pulmonary arteries preventing nitric oxide from acting as a muscle relaxant in vascular walls.

Modifiers of the human mucosal immune system

This review focuses on saliva as a measure of mucosal immunity in man. The review will cover studies of parameters that modify the early ontogeny patterns of mucosal immunity and the impact of infections and physiological variables on the human mucosal immune system. The most significant modifiers of human mucosal immunity are events that occur in the neonatal maturation period and, later in life, the interplay between the immune system and the neuroendocrine systems. IgA antibodies are the predominant isotype involved in the human mucosal immune response and are important for protection at mucosal surfaces. The level of IgA in mucosal secretions is modified by antigenic stimulation as well as by many physiological variables. Studies have also revealed that IgM plays a significant immunoregulatory role at mucosal surfaces, particularly during episodes of infection or stress. The detection patterns of IgD in saliva of neonates suggests a role for IgD in the initial maturation process of mucosal immunity. The role of IgG at mucosal surfaces is unclear and although IgG may play a compensatory role in IgA deficiency, the detection of high levels of IgG in saliva appears to be associated with periods of increased membrane permeability.

Sudden infant death syndrome (SIDS): immunoglobulins and hypoxia

A body of opinion suggests that immunological overstimulation of the gastrointestinal and respiratory mucosa is involved in SIDS. The local stimulation of immunoglobulin concentration in the respiratory mucosa is said to be the consequence of an accentuated reaction to a trivial infection (1-4). One hypothesis is that an accentuated airways reactivity plays a key role in the events leading to SIDS and cites the final insult as oxygen lack, low oxygen stores, high oxygen usage and cardiorespiratory failure (5). We hypothesize that hypoxia and antioxidants exacerbate disorders of the paracrine interaction in the airways mucosa leading to overproduction of immunoglobulins. Administration of vitamin E above dietary needs to hypoxic chicks increased the immune response. The effects were considered synergistic in elevated production of immunoglobulins, and in their function as antioxidants (6). The oxygen lack, low oxygen stores, high oxygen usage and cardiorespiratory failure (5) are factors capable of provoking an overstimulated immune response in the respiratory mucosa. When levels of T-helper/inducer cells are maintained in AIDS patients' blood plasma, survival time is extended (7). This paper investigates the role of 1,25 (OH) 2D3 in suppression of T-helper/inducer lymphocyte activity in vitro (8,9,34,36), and the failure of activated pulmonary alveolar macrophages (PAM) to produce sufficient 1,25(OH)2D3 to inhibit beta-cell proliferation before differentiation to immunoglobulin secreting cells (4,36).

Retrograde axonal cytokine transport: a pathway for immunostimulation in the brain inducing hypoxia and sudden infant death?

The etiology and pathogenesis of sudden infant death syndrome (SIDS) remain unknown. A hypothesis for SIDS should explain three characteristic findings: (a) an age distribution peaking at 2-4 months; (b) frequent association with respiratory tract infections; and (c) occurrence during sleep. The diagnosis of SIDS is applied when death cannot be explained, and this syndrome therefore probably includes various underlying causes. Based on recent observations, however, we suggest a pathogenic pathway that might be common to most SIDS victims.

The anaphylaxis hypothesis of sudden infant death syndrome (SIDS): mast cell degranulation in cot death revealed by elevated concentrations of tryptase in serum

A series of cases of sudden unexpected post-neonatal deaths from two centres in the UK have been investigated for evidence of mast cell activation using the biochemical markers tryptase and 9 alpha,11 beta-PGF2. Tryptase was selected as a possible marker because it is a component of mast cell secretory granules and, unlike histamine, it is not released from basophils. The prostaglandin 9 alpha,11 beta-PGF2 is an initial and pharmacologically active metabolite of PGD2, the major mast cell-derived cyclooxygenase product. This prostaglandin was chosen to serve as a marker of newly generated mediator release. In the study, unexplained infant deaths were associated with a higher concentration of tryptase in serum compared with cases of unexpected, but subsequently explained death. However, 9 alpha,11 beta-PGF2 was found to be an unsuitable post mortem marker in this situation. These results provide direct evidence that mast cell degranulation, possibly as a result of anaphylaxis, may be occurring around the time of death in some cases of cot death.

Vitreous humor hypoxanthine levels in SIDS and infectious death

Hypoxanthine concentrations in vitreous humor were determined in 107 cases of sudden infant death syndrome (SIDS) and compared with levels in 4 cases of borderline SIDS, 26 cases of infectious death and 16 cases of sudden violent death. The hypoxanthine measurements were made using a high-performance liquid chromatography method. The hypoxanthine levels were significantly (p < 0.01) higher in SIDS than in violent deaths, while no significant difference was found between SIDS and infectious deaths. The present report demonstrates a similar distribution pattern of hypoxanthine levels in vitreous humor in SIDS and infectious death. We have previously described signs of immune stimulation both in peripheral organs and in the central nervous system in these conditions. This indicates that the death mechanism in SIDS has some similarities with infectious death.

Is partial deletion of the complement C4 genes associated with sudden infant death?

The two C4 loci C4A and C4B in 61 cases of sudden infant death (SID), 93 living controls and 7 cases of infectious death were studied. In the SID group 13.1% showed deletion of the C4A gene, while 2.5% of the cases showed deletion of the C4B gene. This was not significantly different from neither the controls nor the infectious death group. We were not able to confirm that deletion of the C4B gene is associated with SID. However, in the SID group deletion of either the C4A or the C4B gene was associated with signs of infections prior to death (P = 0.035). This observation may indicate that a proportion of SID victims are more vulnerable to infections than other infants.

Development of immune response markers in the trachea in the fetal period and the first year of life

Immunoglobulin (Ig)-producing cells, T cells (CD3) and epithelial expression of secretory component (SC) and HLA class II determinants (DR, -DP, -DQ) were studied by immunohistochemistry in 16 fetal and 15 postnatal specimens from the tracheal wall. Small amounts of secretory component (SC) was present in the tracheal surface and gland epithelium in the fetal period and increased towards term. A few IgM-, IgD- and IgG-producing cells were present in some fetal specimens but no IgA- and IgE-producing cells were found. Only very few CD3+ T-cells were present in fetal specimens and intraepithelial T-cells were virtually absent until after birth. Premature infants that lived for 1 week had less SC epithelial expression than mature infants of the same age. The density of CD3+ T-cells, IgA-, IgM-producing cells as well as the epithelial SC expression increased rapidly after birth. Epithelial MHC class II expression was absent in fetal specimens. HLA-DR was detected on the apical border of the surface epithelium one week after birth and was extensively expressed throughout the remaining postnatal period. Epithelial DP and PQ expression were virtually absent during this same period. These features probably reflect local activation of the immune system in response to environmental factors.

Post-mortem concentrations of hypoxanthine in the vitreous humor--a comparison between babies with severe respiratory failure, congenital abnormalities of the heart, and victims of sudden infant death syndrome

Post-mortem hypoxanthine concentrations in the vitreous humor of human infants were investigated. Hypoxanthine is formed from hypoxic degradation of adenosine monophosphate. The concentrations in the vitreous humor can give information about antemortem hypoxia. The post-mortem levels were corrected for the time elapsing between death and the autopsy. Four groups of infants were compared: 17 babies who died of respiratory distress syndrome (RDS), 72 infants who died of sudden infant death syndrome (SIDS), 23 children dying of congenital heart disease (both cyanotic and acyanotic), and 15 children dying acutely in accidents without any known significant time of hypoxia before death. The corrected, median hypoxanthine levels in victims of SIDS (200 mumol/L) was significantly higher (p < 0.01) than in the accident group (0 mumol/L), but no clear difference was found between the SIDS group and the RDS group (101 mumol/L), or the heart group (54 mumol/L). A number of children with "normal" hypoxanthine levels (0 to 38 mumol/L) were found in all four groups, but the numbers were significantly lower (p < 0.005) in the RDS, SIDS and heart groups than in the accident group. It is concluded that SIDS is probably not a sudden event, but may be preceded by relatively long, or repeated intermittent periods of hypoxia (of unknown etiology).

Contemporary risk factors for sudden infant death in an Irish population--a case control study

This case-controlled study examines some recently implicated risk factors for Sudden Infant Death Syndrome (S.I.D.S.) in Irish infants. Irish S.I.D.S. infants are lighter at birth than controls (3463g) compared to (3542g) and boys out-number girls by a ratio of 1.3:1. S.I.D.S. infants are more frequently: breast-fed (42% vs 25%) and sleep in a location other than the parent's bedroom (54% vs 21%), but start solids at a similar age and appear not to be sicker prior to death than the control group. This study highlights the frequency of symptoms of possible ill-health (i.e. snuffles and being "chesty") in well infants during the first months of life with 32% of the control group having snuffles and 35% described as "chesty". In addition these symptoms are frequently treated with antibiotics with 31% of the control group having already received antibiotics by 2 months of age. A majority of S.I.D.S. infants were described as cold when found (52%) with 39% described as warm and 15% as sweaty. Obviously the recently implicated role of overheating may be relevant in the latter 15% of S.I.D.S. cases. In this series, 88% of infants had died by 6 months of age. Of the 97 parents of S.I.D.S. infants questioned, 78 had subsequently become pregnant by the time the study was conducted at an average time of 5 months post the S.I.D.S. event.

A seasonal association between SIDS deaths and kindergarten absences

Data from linked birth and death certificates from the State of Oregon were used to determine the monthly distribution of deaths from sudden infant death syndrome (SIDS) for the years 1976 through 1984. The monthly number of SIDS deaths increased in winter and decreased in summer, when schools usually are not in session. Absences from kindergarten were determined from school records for the period 1979-84. School absences, previously shown to reflect incidence of predominantly infectious diseases, were found to be positively correlated with occurrences of SIDS. The role of ordinarily nonlethal infections in occurrences of SIDS has been established by history, histology, and viral isolation. The authors concluded that the seasonality of SIDS is related to the seasonality of respiratory infections and that the seasonality is influenced by respiratory infections being spread from school children to infants during periods when schools are in session.

Review of the epidemiology of sudden infant death syndrome and its relationship to temperature regulation

Infants dying suddenly and unexpectedly now account for 20% of all infant deaths in England and Wales, and the incidence shows no sign of falling. Recent work relating sudden infant death to a raised environmental temperature and a raised body temperature, implicates fever as a possible contributory cause of death; some infants may be unable to control their febrile response to infection, or to thermoregulate effectively, when well wrapped and heated. Death might then result from apnoea, occurring in a critical sleep state. These ideas have increased the interest in describing the normal practices of parents in caring for the environment of their infants in health and disease, and the effect of their behaviour on the child's temperature. Studies of these areas depend on collecting and interpreting data from young children during their day to day lives, and present a challenge of great relevance to primary care research.