Sharron T. Hall

Cytokine responses and sudden infant death syndrome: genetic, developmental, and environmental risk factors

Despite the success of the campaigns to reduce the risk of sudden infant death syndrome (SIDS), it still remains the major cause of postneonatal mortality. The incidence of SIDS is higher among ethnic groups in which there are also high incidences of serious infectious diseases. The risk factors for SIDS parallel those for susceptibility to infection, and recent data have provided evidence to support the mathematical model of the common bacterial toxin hypothesis. One current hypothesis for the etiology of SIDS is that the deaths are a result of overwhelming proinflammatory responses to bacterial toxins; as in inflammatory responses to sepsis, cytokines, induced by bacterial toxins, cause physiological changes leading to death. The genetic, developmental, and environmental risk factors for SIDS are reviewed in relation to colonization by potentially harmful bacteria and the inflammatory responses induced in the nonimmune infant to microorganisms or their products.

SALIVARY IGA SUBCLASSES AND INFECTION RISK IN ELITE SWIMMERS

The concentrations of total IgA, IgA1 and IgA2 were measured in saliva collected from 25 elite swimmers in the early and late phases of a 7 month training season and compared with the number of respiratory infections during the season. The IgA1 concentrations in the early phase of the training season were significantly associated (P = 0.01) with the number of respiratory infection episodes during the training season. The lower the concentration of IgA1, the greater the number of infection episodes. Swimmers with four or more infections during the training season had significantly lower salivary IgA1 concentrations than those with less than four infection episodes (P = 0.01). The proportion of IgA1 in the saliva of the elite swimmers (80%) was higher than for normal non‐exercising adults (60%). A small proportion of athletes had salivary IgA2 concentrations below the detection limit of the assay and the mean concentration of IgA2 was significantly lower than the concentrations for a normal adult population (P = 0.01). This study suggests that measurement of IgA subclasses, in particular IgA1, at the commencement of a training season may predict infection risk in elite swimmers.

The measurement of IgA and IgG transglutaminase antibodies in celiac disease: a comparison with current diagnostic methods

Summary Celiac disease (CD) is an inflammatory disorder of the small intestine induced by cereal prolamins. The demonstration of IgA endomysial antibodies (EMA) is currently the most reliable serological screen for CD. The antigenic target is transglutaminase. The aim of this study was to develop an ELISA assay for the detection of antibodies to transglutaminase (TGA), and to assess the sensitivity and specificity of TGA for the detection of celiac disease against the benchmarks of jejunal biopsy, antigliadin antibodies (AGA) and EMA. Sera from 57 patients with celiac disease were tested for IgA and IgG TGA, IgA EMA, IgA and IgG AGA, and the total IgA level. The sensitivity, specificity, predictive value and concordance of AGA, EMA and TGA were assessed against the gold‐standard biopsy result. IgG plus IgA TGA offered 100% sensitivity in CD patients for whom no dietary intervention had been commenced, with a specificity of 61%. The sensitivity of TGA dropped from 100 to 79% after dietary restriction. In patients on no gluten restriction, there was 100% agreement between TGA and EMA, and 100% agreement between TGA and AGA for the IgA isotype. The false‐positive rate for TGA was 53% in Downs syndrome patients and 25% in patients with systemic autoimmune disorders. We conclude that testing for TGA is a reliable diagnostic serology for celiac disease, with improved sensitivity compared with established methods. The results suggest that serial TGA measurements may be a more accurate marker for dietary compliance than AGA, but prospective studies are required.Abbreviations: ARA, anti‐reticulin antibodies; AGA, anti‐gliadin antibodies; CD, celiac disease; EMA, endomysial antibodies; SSA, Sjogrens Syndrome Antigen ‘A’; TU, transglutaminase units.

The male excess in sudden infant deaths

The peak age at which sudden infant death syndrome (SIDS) occurs corresponds to the developmental period in which infants are dependent on their innate responses to infection. There is a growing body of evidence indicating that dysregulation of inflammatory responses might contribute to the physiological changes leading to these sudden deaths. This study examined the effects of three important risk factors for SIDS on inflammatory responses: cigarette smoke, virus infection and male sex. Cytokine responses of peripheral monocytic blood cells of healthy, non-smoking males and females to endotoxin were measured. Surrogates for virus infection or cigarette smoke were assessed using IFN-γ or water-soluble cigarette smoke extract (CSE). For most conditions, cells from males had lower pro-inflammatory cytokine responses than those of females. An opposite trend was observed for IL-10. Significantly lower levels of some cytokines were noted for cells from male donors exposed to CSE. In females, there were significant correlations between testosterone levels and levels of pro-inflammatory cytokines, but none for males. Testosterone levels in females correspond to those among male infants in the age range at greatest risk of SIDS. The effects of the testosterone surge in male infants need to be examined in relation to changes in cortisol levels that occur during the same period of infant development.

Exploring the Risk Factors for Sudden Infant Deaths and Their Role in Inflammatory Responses to Infection

The risk factors for sudden infant death syndrome (SIDS) parallel those associated with susceptibility to or severity of infectious diseases. There is no evidence that a single infectious agent is associated with SIDS; the common thread appears to be induction of inflammatory responses to infections. In this review, interactions between genetic and environmental risk factors for SIDS are assessed in relation to the hypothesis that many infant deaths result from dysregulation of inflammatory responses to “minor” infections. Risk factors are assessed in relation to three important stages of infection: (1) bacterial colonization (frequency or density); (2) induction of temperature-dependent toxins; (3) induction or control of inflammatory responses. In this article, we review the interactions among risk factors for SIDS for their effects on induction or control of inflammatory responses. The risk factors studied are genetic factors (sex, cytokine gene polymorphisms among ethnic groups at high or low risk of SIDS); developmental stage (changes in cortisol and testosterone levels associated with 2- to 4-month age range); environmental factors (virus infection, exposure to cigarette smoke). These interactions help to explain differences in the incidences of SIDS observed between ethnic groups prior to public health campaigns to reduce these infant deaths.

Cytokine Levels in Late Pregnancy: Are Female Infants Better Protected Against Inflammation?

Inflammatory responses have been implicated in several forms of infant deaths (sudden expected deaths and stillbirths) and the initiation of pre-term births. In this study, we examined matched samples of term maternal blood, cord blood, and amniotic fluid obtained from 24 elective cesarean deliveries for both pro- and anti-inflammatory cytokines thought to be important in maintaining a balanced response leading to successful pregnancy outcome. These included interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), IL-10, and IL-1 receptor antagonist (IL-1ra). Amniotic fluid levels for each of the cytokines examined were significantly higher than those for cord blood or maternal plasma. While pro-inflammatory cytokines were higher in amniotic fluid associated with male fetuses compared with females, the major significant difference was higher levels of IL-1ra in amniotic fluid associated with female fetuses. Our study supports similar findings for cytokines during mid-trimester, which noted that amniotic fluid levels were higher than those in maternal blood. Our study suggests that maternal decidua secretes additional IL-ra in the presence of a female conceptus which improves the likelihood of a good outcome compared to pregnancies with male fetuses.

Effects of gender, cytokine gene polymorphisms and environmental factors on inflammatory responses.

Previous studies have indicated that cytokine gene polymorphisms of Indigenous Australians were predominantly associated with strong pro-inflammatory responses. We tested the hypothesis that cells of donors with genetic profiles of inflammatory cytokine single nucleotide polymorphisms (SNPs) similar to Indigenous Australians produce higher pro-inflammatory responses. PBMCs from 14 donors with genetic profiles for a high risk of strong pro-inflammatory responses and 14 with low-risk profiles were stimulated with endotoxin and effects of gender, IFN-γ, cigarette smoke extract (CSE) and testosterone on cytokine responses analysed. Cytokines were calculated from standard curves (Luminex 2.3 software). No significant differences were associated with SNP profile alone. Lower pro-inflammatory responses were observed for cells from males with low- or high-risk profiles. For cells from females with high-risk profiles, anti-inflammatory IL-10 responses were significantly reduced. There was no effect of testosterone levels on responses from males. For females, results from IFN-γ-treated cells showed positive correlations between testosterone levels and IL-1β responses to endotoxin for both risk groups and TNF-α for the high-risk group. If interactions observed among CSE, IFN-γ, genetic background and testosterone reflect those in vivo, these might contribute to increased incidences of hospitalisations for infectious diseases among Indigenous women.

Comparison of cytokine gene polymorphisms among Greek patients with invasive meningococcal disease or viral meningitis

High levels of pro-inflammatory cytokines are implicated in the severity of invasive meningococcal disease (IMD) and viral meningitis (VM). This study compared single-nucleotide polymorphisms (SNPs) in pro- and anti-inflammatory cytokine genes among patients with VM or IMD. Patient DNA samples were prepared by the National Meningitis Reference Laboratory in Athens: n=98 for IMD and n=53 for VM. The results for both patient groups were compared with data published for healthy Greek control data. Real-time PCR was used to assess the interleukin (IL) gene SNPs IL6 G-174C, IL1B C-511T, IL1RN T+2018C, IL10 G-1082A and IL8 A-251T and the tumour necrosis factor α (TNF-α) SNP TNFA G-308A. Differences were compared by Fishers exact test. The genotype for high IL-6 responses was predominant among IMD (51%, P=0.0008) and VM (74.5%, P<0.0001) patients compared with the controls (31%). The genotype associated with high TNF-α responses was 5% among controls and lower for IMD (1.1%, P=0.0014) and VM (0%, P=0.052). There was no difference for IL-8 SNPs between controls and IMD (P=0.162), but the difference was significant for VM (P=0.0025). IL-6 (P=0.024) and IL-8 (P=0.00004) SNPs differed between IMD and VM. Reports on associations between IL-8 SNPs and cytokine responses differ. Because of its role in neutrophil attraction, differences in frequencies of the IL-8 SNP for IMD and VM require further investigation.

Effects of Maternal Inflammation and Exposure to Cigarette Smoke on Birth Weight and Delivery of Preterm Babies in a Cohort of Indigenous Australian Women

Sudden infant death syndrome (SIDS), neonatal deaths, and deaths from infection are higher among Indigenous Australians. This study aimed to determine the effects of inflammatory responses and exposure to cigarette smoke, two important factors associated with sudden death in infancy, on preterm birth, and birth weight in a cohort of Indigenous mothers. Indigenous Australian women (n = 131) were recruited as part of a longitudinal study while attending antenatal care clinics during pregnancy; blood samples were collected up to three times in pregnancy. Serum cotinine, indicating exposure to cigarette smoke, was detected in 50.4% of mothers. Compared with non-Indigenous women, the cohort had 10 times the prevalence of antibodies to Helicobacter pylori (33 vs. 3%). Levels of immunoglobulin G, antibodies to H. pylori, and C-reactive protein (CRP) were all inversely correlated with gestational age (P < 0.05). CRP levels were positively associated with maternal body mass index (BMI; ρ = 0.449, P = 0.001). The effects of cigarette smoke (cotinine) and inflammation (CRP) were assessed in relation to risk factors for SIDS: gestational age at delivery and birth weight. Serum cotinine levels were negatively associated with birth weight (ρ = −0.37, P < 0.001), this correlation held true for both male (ρ = −0.39, P = 0.002) and female (ρ = −0.30, P = 0.017) infants. Cotinine was negatively associated with gestational age at delivery (ρ = −0.199, P = 0.023). When assessed by fetal sex, this was significant only for males (ρ = −0.327, P = 0.011). CRP was negatively associated with gestational age at delivery for female infants (ρ = −0.46, P < 0.001). In contrast, maternal BMI was significantly correlated with birth weight. These data highlight the importance of putting programs in place to reduce cigarette smoke exposure in pregnancy and to treat women with chronic infections such as H. pylori to improve pregnancy outcomes and decrease risk factors for sudden death in infancy.

Development of an experimental model for assessing the effects of cigarette smoke and virus infections on inflammatory responses to bacterial antigens

Interactions among major risk factors associated with bacterial infections were assessed in a model system using surrogates for virus infection; IFN-g, and exposure to cigarette smoke; cigarette smoke extract (CSE), nicotine and cotinine. Cytokine responses elicited by LPS from THP-1 cells in the presence of these components, or combinations of components, were assessed by multiplex bead assay, i.e. IL-1β, IL-6, IL-8, IL-10, TNF-α and IFN-γ. IFN-γ-priming significantly increased pro-inflammatory cytokines induced by LPS. CSE suppressed production of pro-inflammatory cytokines IL-1β, TNF-α and IFN-γ, but enhanced production of IL-8. Nicotine and cotinine suppressed all cytokine responses. In combination, IFN-γ masked the inhibitory effects of CSE. In relation to the objectives of the study, we concluded that (a) IFN-γ at biologically relevant concentrations significantly enhanced pro-inflammatory responses; (b) CSE, nicotine and cotinine dysregulated the inflammatory response and that the effects of CSE were different from those of the individual components, nicotine and cotinine; (c) when both IFN-γ and CSE were present, IFN-γ masked the effect of CSE. There is a need for clinical investigations on the increase in IL-8 responses in relation to exposure to cigarette smoke and increased pro-inflammatory responses in relation to recent viral infection.