Risk Assessment in Immunotoxicology: I. Sensitivity and Predictability of Immune Tests

We have previously reported on the design and content of a screeningbattery involving a "tier" approach for detecting potentialimmunotoxic compounds in mice (Luster et al., 1988, Fundam.Appl. Toxicol. 10, 2–19). This battery has now been utilizedto examine a variety of compounds by the NIEHS ImmunotoxicologyLaboratory, the National Toxicology Programsponsored laboratories,and by the Cell Biology Department at the Chemical IndustryInstitute of Toxicology. The database generated from these studies,which consists of over 50 selected compounds, has been collectedand analyzed in an attempt to improve future testing strategiesand provide information to aid in quantitative risk assessmentfor immunotoxicity. Studies presented here have establishedthe ability of each of the tests or test combinations in thescreening battery to detect immunotoxic compounds. Efforts arecurrently underway using this database to determine the relationshipsbetween these immune tests and susceptibility to challenge withinfectious agents or transplantable tumor cells. The presentanalyses indicated that the performance of only two or threeimmune tests are sufficient to predict immunotoxic compoundsin rodents (>90% concordance). The tests that showed thehighest association with immunotoxicity were the splenic antibodyplaque forming cell response (78%) and cell surface marker analysis(83%). The relationship between immunotoxicity and carcinogenicity,as well as genotoxicity, was also determined. These analysessuggested that potential immunotoxic compounds are likely tobe rodent carcinogens (p = 0.019) although for compounds thatare not immunotoxic the carcinogenic status is unclear. Therewas no relationship observed between immunotoxicity and mutagenicityas determined using in vitro genotoxicity tests. The significanceof these observations is discussed in terms of the relationshipbetween immunotoxicity tests and biological/toxicological processesconcerned with human health (e.g., infectious disease).     

Streptococcus pneumoniae-induced haemolytic uraemic syndrome

Haemolytic uraemic syndrome secondary to infection with neuraminidase producing Streptococcus pneumoniae is well recognised, but was previously considered to be rare. This case report describes the course of a 9-month-old male with pneumococcal pneumonia, T activation and haemolytic uraemic syndrome. The clinical features of three other cases treated in Southeast Queensland in the past 2 years and 12 previously reported cases are summarised. The widespread availability of rapid diagnostic testing for this entity should allow for increased recognition, enabling appropriate use of low plasma volume blood products with improved patient outcome.     

Delivery of salbutamol by metered dose inhaler and valved spacer to wheezy infants: effect on bronchial responsiveness

The efficacy of a new valved spacer device, the Babyhaler inhaler (Glaxo) for administering metered dose inhaler treatment via a facemask to infants was assessed. In a double blind, single dose study, salbutamol (800 micrograms) or placebo were given on separate days to 12 sedated, sleeping, wheezy infants during a symptom free interval. Lung function was measured before and after administration and the bronchial response to aerosol challenge with methacholine was then assessed using the squeeze technique. A small increase in heart rate and a drop in arterial oxygen tension followed salbutamol administration. No other change in lung volume or air flow obstruction was detected. Bronchial responsiveness decreased significantly after the administration of salbutamol by Babyhaler, the PC30 (provoking concentration of methacholine causing a 30% fall in maximal flow at functional residual capacity by the squeeze technique) increasing from a median of 3.8 g/l after placebo to 12.5 g/l after salbutamol. The Babyhaler is an effective device for administering bronchodilator to wheezy infants. The small scale of the response may be attributable to the uncertain effect of beta agonists in this population. Furthermore, pulmonary deposition of inhaled aerosols may be reduced in nose breathing, sleeping infants.     

Hypoxaemia in infants with respiratory tract infections

Nineteen infants who were graduates from special care baby units underwent two overnight tape recordings of oxygen saturation (SaO2) and breathing movements; one during an upper (n = 12) or lower (n = 7) respiratory tract infection and the other when free of infection. Baseline SaO2 was lower during infection (median 99.6 vs 100%, p less than 0.01), with four patients having values (84.3-95.5%) below the normal lower limit for full-term infants (97%). The median number of apnoeic pauses was also lower during respiratory tract infection (4.7 vs 15.7/h, p less than 0.02). The median number of episodic desaturations (SaO2 less than or equal to 80%) did not change significantly (1.3 vs 1.9/h, p greater than 0.05), with the exception of one patient who had extremely increased values during infection for both apnoeic pauses (63/h) and desaturations (112/h). No infant, however, was considered clinically hypoxaemic. Clinically unsuspected hypoxaemia may thus occur during respiratory tract infection in a proportion of infants graduating from special care baby units. Such hypoxaemia may have potentially deleterious effects.     

Epidemiology of persistent diarrhea among Guatemalan rural children

A prospective, longitudinal two-year study to determine the epidemiology of persistent ( 14 days'duration) diarrhea in rural children of Guatemala was undertaken. Three-hundred and twenty-one children aged 0-35 months were kept under surveillance by twice-a-week home visits. The overall incidence of diarrhea was 0.147 per child-week; the incidence of persistent diarrhea was 0.014 per child-week. The peak of persistent diarrhea was observed in infants below six months of age, with a continuous decline thereafter. This trend in incidence of persistent diarrhea was associated with a higher proportion (16%) of illnesses persisting for more than 13 days in children younger than six months of age as compared to children 30-35 months old (4%). Males had more diarrhea (0.156 per child-week) than females (0.139 per child week). Among children above 18 months of age, the proportion of episodes that lasted for more than 13 days was lower in females than in males.     

Oncogenicity Testing of 2-Ethylhexanol in Fischer 344 Rats and B6C3F1 Mice

2-Ethylhexanol (2EH) is a weak nongenotoxic hepatic peroxisomeproliferator in the rat. It is a high-volume chemical intermediatein the preparation of the plasticizers bis-(2-ethylhexyl) adipate(DEHA), bis-(2-ethylhexyl) phthalate (DEHP), and tris-(2-ethylhexyl)phosphate (TEHP), which are weak hepatocellular tumorigens infemale mice. In consequence, the oncogenic potential of 2EHwas evaluated in male (M) and female (F) rats and mice (50 animals/sex/group).Oral gavage doses of 2EH in 0.005% aqueous Cremophor EL (polyoxyl-35castor oil) were given five times a week to rats: 0 (water),0 (vehicle), 50, 150, and 500 mg/kg for 24 months, and to mice:0 (water), 0 (vehicle), 50, 200, and 750 mg/kg for 18 months.Statistical comparisons of data were made between vehicle controlsand treatment groups. There were no differences of biologicalsignificance between data from vehicle and water control groups.In rats, there were no dose-related changes at 50 mg/kg. Therewas reduced body weight gain at 150 mg/kg (M, 16; F, 12%) and500 mg/kg (M, 33; F, 31%) and an increased incidence of lethargyand unkemptness. There were dose-related increases in relativeliver, stomach, brain, kidney, and testis weights at sacrifice.Female rat mortality was markedly increased at 500 mg/kg. Therewas marked aspiration-induced bronchopneumonia in rats at 500mg/kg; hematologic, gross, and microscopic changes, includingtumors, were otherwise comparable among all rat groups. In miceat 50 and 200 mg/kg there were no dose-related changes and essentiallyno time-dependent or time-independent adverse trends in livertumor incidence at the 5% significance level. At 750 mg/kg mousebody weight gain was reduced (M, 26; F, 24%), and mortalityincreased (M and F, 30%) versus vehicle controls. At 750 mg/kgthere was a slight increase in nonneoplastic focal hyperplasiain the forestomach of mice (M 5/50, F 4/50) versus vehicle controls(M 1/50, F 1/50). There were increases in mouse relative liver(F, 21%) and stomach (M, 13%; F, 19%) weights at 750 mg/kg.There was a 12% incidence of hepatic basophilic foci and an18% incidence of hepatocellular carcinomas in male mice at 750mg/kg, not statistically significant compared with either controlby Fisher's exact test. There was a 12% incidence of hepaticbasophilic foci and a 10% incidence of hepatocellular carcinomasin female mice at 750 mg/kg, statistically significant (p <0.05) compared with vehicle but not with water controls by Fisher'sexact test. There were no metastases. Time-dependent and -independentstatistical analyses showed an adverse trend in the incidenceof hepatocellular carcinomas in male and female mice, correlatedwith toxicity (expressed as mortality) at 750 mg/kg. The time-adjustedincidence of hepatocellular carcinomas in male mice (18.8%)was within the historical normal range at the testing facility(0–22%), but that in females (13.1%) lay outside the normalrange (0–2%). Under the conditions of these studies 2EHwas not oncogenic in rats, but there were weak adverse trendsin hepatocellular carcinoma incidence in mice at high dose levelswhich may have been associated with toxicity. The major effectsof chronic dosing were mortality in female rats at 500 mg/kgand in male and female mice at 750 mg/kg, accompanied by reductionsin body weight gain in rats at 150 and 500 mg/kg and in miceat 750 mg/kg. Direct comparison of any tumorogenic effects of2EH given alone to female mice with those due to 2EH formedin vivo from DEHA, DEHP, or TEHP is limited by the high mortalitycaused by 2EH in female mice at equivalent doses of 2EH. While2EH may be a contributing factor in the hepatocellular carcinogenesisin female mice associated with the chronic administration ofDEHA and DEHP, it is unlikely to be the entire proximate carcinogen.