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

Interleukin-1β and interleukin-6 enhance thermal prolongation of the LCR in decerebrate piglets

Thermal stress and prior upper respiratory tract infection are risk factors for the Sudden Infant Death Syndrome. The adverse effects of prior infection are likely mediated by interleukin-1β (IL-1β). Therefore, we examined the single and combined effects of IL-1β and elevated body temperature on the duration of the Laryngeal Chemoreflex (LCR) in decerebrate neonatal piglets ranging in age from post-natal day (P) 3 to P7. We examined the effects of intraperitoneal (I.P.) injections of 0.3mg/Kg IL-1β with or without I.P. 10mg/Kg indomethacin pretreatment on the duration of the LCR, and in the same animals we also examined the duration of the LCR when body temperature was elevated approximately 2°C. We found that IL-1β significantly increased the duration of the LCR even when body temperature was held constant. There was a significant multiplicative effect when elevated body temperature was combined with IL-1β treatment: prolongation of the LCR was significantly greater than the sum of independent thermal and IL-1β-induced prolongations of the LCR. The effects of IL-1β, but not elevated body temperature, were blocked by pretreatment with indomethacin alone. We also tested the interaction between IL-6 given directly into the nucleus of the solitary tract (NTS) bilaterally in 100ngm microinjections of 50μL and pretreatment with indomethacin. Here again, there was a multiplicative effect of IL-6 treatment and elevated body temperature, which significantly prolonged the LCR. The effect of IL-6 on the LCR, but not elevated body temperature, was blocked by pretreatment with indomethacin. We conclude that cytokines interact with elevated body temperature, probably through direct thermal effects on TRPV1 receptors expressed pre-synaptically in the NTS and through cytokine-dependent sensitization of the TRPV1 receptor. This sensitization is likely initiated by cyclo-oxygenase-2 dependent synthesis of prostaglandin E2, which is stimulated by elevated levels of IL-1β or IL-6. Inflammatory sensitization of the LCR coupled with thermal prolongation of the LCR may increase the propensity for apnea and Sudden Infant Death Syndrome.

Is there any correlation between HLA-DR expression in laryngeal mucosa and interleukin gene variation in sudden infant death syndrome?

AIM

The mucosal immune system and cytokines are activated in a large proportion of cases of sudden infant death syndrome (SIDS). Our aim was to search for a possible association between cytokine polymorphisms and immune stimulation of the laryngeal mucosal in SIDS.

METHODS

HLA-DR expression in laryngeal mucosal glands and surface epithelium in 97 SIDS victims was evaluated applying a semi-quantitative scoring system. The findings were related to cytokine gene polymorphisms as well as to the level of various cytokines in the cerebrospinal fluid (CSF). A risk score was established: a score of 0 prepresenting negative HLA-DR, supine position and no fever prior to death.

RESULTS

The IL-6 -176CG/CC genotype was found in 92.3% of the SIDS cases with positive score for all risk factors (p = 0.01). Infants with high HLA-DR score had high levels of IL-6 in the cerebrospinal fluid (>30 μg/L) (p = 0.005). Furthermore, the IL-8 SNPs -781 CT/TT genotypes and -251 AA/AT genotypes were observed in 93% of the SIDS cases with one or more of the risk factors present compared with SIDS cases no risk factors reported (p = 0.003 and p = 0.016, respectively).

CONCLUSION

This study adds further evidence to the hypothesis that there are genetically associated disturbances of immunological homoeostasis 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, 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.

Emotional stress effects on immunity, gingivitis and periodontitis

Gingivitis and periodontitis are thought to result from an imbalance between those oral microorganisms which normally colonize tooth surfaces in close contact with the gingival margin, and the nature and efficiency of the host response. The bacteria are the triggering agents, but host defence mechanisms within the gingival/periodontal tissues seem to be responsible for most of the tissue damage and for the outcome and progression of the diseases. It has recently been shown that emotional or psychological load (stress) may influence immune activities directly via nerve messenger substances (neurotransmitters and neuropeptides) and/or indirectly via neuroendocrine (hormone) substances. This review discusses how emotional stressors and nervous and neuroendocrine responses to psychological stressors may modulate the immune response to bacteria, and thus be expected to influence the progression and course of gingivitis and periodontitis.