An early commitment to expression of a particular TCRVbeta chain on CD8(+) T cells responding to attenuated Plasmodium berghei sporozoites is maintained following challenge with infectious sporozoites.

Protection induced by irradiated Plasmodium berghei sporozoites (Pbgamma-spz) in mice is linked to CD8(+) T cells specific for exo-erythrocytic-stage Ags, and intrahepatic memory CD8(+) T cells are associated with protracted protection. However, the Ag specificity of the protective CD8(+) T cells remains largely unknown. In this study, we characterized the TCR Vbeta usage by intrahepatic CD8(+) T cells during gamma-spz immunization and after the challenge with infectious Pb sporozoites. The repertoire of naïve (T(N)) and central memory (T(CM)) CD8(+) T cells was diverse and conserved between individual mice, and did not change with immunization. In contrast, preferential usage of one or more TCR Vbeta subset was observed in effector memory (T(EM)) CD8(+) T cells after immunization. The expanded TCR Vbeta varied between individual mice but Vbeta4, 6, 7, 8.3, 9 and 11 were the most frequently expressed. In addition, there was a correlation in the TCR Vbeta usage by gamma-spz-induced CD8(+) T(EM) in the liver and blood of individual mice. The expansion pattern of blood CD8(+) T(EM) did not change with challenge and remained the same for 8 weeks thereafter. These results demonstrate that immunization with gamma-spz skews the TCR Vbeta repertoire of CD8(+) T(EM), and commitment to a particular TCR Vbeta expression is maintained long-term.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is associated with hyperinsulinemia and insulin resistance.

High exposures of Vietnam veterans to 2,3,7, 8-Tetrachlorodibenzo-p-dioxin, a dioxin contained in the herbicide mixture Agent Orange, have previously been demonstrated to be associated with an increased prevalence of diabetes and hyperinsulinemia in non-diabetic subjects. Sixty-nine persons were identified who were in good health and had normal glucose levels during glucose tolerance testing. These subjects lived within 25 miles of the Vertac/Hercules Superfund site located in Jacksonville, Arkansas. The blood sera lipid concentrations of TCDD for the 69 subjects ranged between 2 and 94 ppt. When subjects with blood sera lipid TCDD levels in the top 10% (TCDD > 15 ppt, n = 7) were compared to subjects with lower levels (2-15 ppt, n = 62), there were no group differences in age, obesity, gender distribution, total lipids, or glucose levels. However, plasma insulin concentrations, at fasting and 30, 60, and 120 min following a 75 g glucose load, were significantly higher in the group with high blood TCDD levels. These finding could not be explained by other known risk factors for hyperinsulinemia. The finding of the TCDD-hyperinsulinemia relationship is consistent with studies of Vietnam veterans and suggests that high blood TCDD levels may cause insulin resistance.

Neurotoxicity of mercury--indicators and effects of low-level exposure: overview.

The theme of the Twelfth International Neurotoxicology Conference was Neurotoxicity of Mercury: Indicators and Effects of Low-Level Exposure. Papers related to the topic appear in NeuroToxicology 16(4):1995 and 17(1):1996 (this issue). This overview provides the reader with a guide by discussing the papers under the topics of human exposure, human health effects, risk assessment, mechanism of action, and primate models.

Prenatal chlordane exposure: effects on plasma corticosterone concentrations over the lifespan of mice.

Developmental exposure to nonteratogenic doses of the organochlorine pesticide Chlordane has been reported to alter endocrine function of apparently normal offspring evaluated at 101 days of age (J.S. Cranmer, D.L. Avery, R.R. Grady, and J.S. Kitay, 1978, J. Environ. Pathol. Toxicol. 2, 357-369). The long-term study reported here was conducted in cohort groups of identically treated mice to determine if prenatal exposure to Chlordane had a persistent effect on endocrine function over the lifespan of the exposed offspring as determined by alterations in plasma concentrations of corticosterone at 400 and 800 days of age. Dihybrid female mice were exposed throughout gestation to 0.16 or 8.00 mg/kg/day Chlordane and endocrine function of offspring was evaluated at three timepoints in their lifespan. Adrenal production and liver reduction capacity for corticosterone (the primary glucocorticoid in rodents) and plasma concentration of corticosterone were measured at 101 days. In this and three previous studies, changes in plasma levels of corticosterone proved to be a reliable indicator of changes in adrenal and/or liver function, thus, only plasma concentrations of corticosterone were determined at 400 and 800 days of age. Plasma corticosterone concentrations of male mice prenatally exposed to the lower Chlordane dose were significantly (P less than 0.01) elevated when measured at 101 days of age. This abnormal elevation (P less than 0.05) was recorded in both dose groups when male mice were examined at 400 days of age. At 800 days of age, no differences from control were found for male offspring in the lower dose group; insufficient numbers of offspring in the higher dose group survived to be evaluated. An effect of Chlordane on corticosterone metabolism in female offspring was observed only in the 0.16 mg/kg dose group at 400 days of age when plasma concentrations of corticosterone were significantly (P less than 0.05) increased. Results suggest that prenatal exposure to nonteratogenic doses of Chlordane (1) had a significant effect on endocrine function (corticosterone control), (2) affected males more than females, and (3) produced changes (increased plasma corticosterone levels) which were detectable at adulthood and persisted into middle age. The mechanisms responsible for these persistent changes in corticosterone metabolism remain to be elucidated.

NCTR computer systems designed for toxicologic experimentation. I. Overview.

Established in 1971 by the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA), the National Center for Toxicological Research is committed to the study of long-term, low-dose effects of potentially toxic substances, including carcinogens. The Scientific Information Systems Division (SISD) facility provides logistic support for complex experiments involving large numbers of test animals. Animal population at the Center, including the breeding colony and animals on experiment, can be as high as 80,000. Each animal must be accounted for, fed and watered under strict control, and continually observed. From birth to final examination, an individual animal might have as many as 3,000 individual elements of information associated with it. This paper introduces a series of reports dealing with an integrated and comprehensive system of experiment planning and implementation (including information gathering, classification, analyses and reporting), employing state-of-the-art data processing techniques. This extensive use of computer technology has permitted the collection, proper classification, and rapid retrieval of virtually error-free data, resulting in cost-sensitive experiment planning.

Effects of diphenylhydantoin and chloroquine on monkey liver microsomal mixed-function oxidases.

Sixteen adult male squirrel monkeys (Saimiri sciureus) were randomly divided into three treatment groups and one control group. Each treatment group received 10 mg/kg oral doses of diphenylhydantoin and/or chloroquine. Following sacrifice, in vitro assays for activity of liver microsomal mixed-function oxidases were run. The assays confirmed diphenylhydantoin as a potent inducer of mixed-function oxidases. Chloroquine administration had little affect on the enzymes assayed and did not inhibit the diphenylhydantoin induction.

Estimation of risks due to environmental carcinogenesis.

Several Federal agencies share responsibility for enforcing laws designed to control human exposures to carcinogens. This enforcement activity often has immense effects on other factors of our environment. Absolute safety is not possible, but increased protection is obtainable. Improvements are urgently needed in our ability not only to detect but also to quantify relative risk. Resources should be directed for maximum overall effect. Relative risk must be quantified if we are to reasonably compare risk and benefit. Examples of the inexactness of current toxicological, epidemiological, and mathematical models for estimating risk due to exposures to DDT, aflatoxinb1, DES, and benzidine are presented. The impact of different laws and regulations applicable to the control of these agents is compared. Reference is made to major programs in toxicological methods for risk estimation.

Research data integrity: a result of an integrated information system.

The toxicologic problems of today frequently require long-term, multidisciplinary experimentation involving large numbers of animals. In order to provide the extensive safety evaluation necessary to produce data that can be reasonably extrapolated to humans, automated research support systems have transcended the position of useful tools and have become an integral part of the total design of experimental protocols. For an automated information system to fully represent the reality of the experiment, it must be able to assure integrity, as well as provide for the storage, calculation, and retrieval of data values of the quality and quantity necessary for fulfilling protocol requirements. Guarantees against error and loss of data, in addition to flexibility and easy access, must be an inherent part of the system if the acceptance and condifence of the investigator are to be obtained. This paper discusses the criteria, philosophies, and benefits of integrated data systems that ensure integrity of toxicologic research support.

Advances in animal care technology at the National Center for Toxicological Research.

The research purpose of the NCTR as it relates to animal care emphasizes the improvement of protocols for safety assessments, the study of irreversible lesions, and the use of valid animal models. The development, building, and operation of the "A" Barrier were described. The "A" Barrier is a complex of equipment, instrumentation, and rooms with controlled entry designed to prevent introduction of microoranisms or environmental factors into the SPF animal colonies. Support facilities such as computer controls and pathology were also described. The first experimental compound being tested is 2-acetylaminofluorene (2-AAF) which will be administered to a total of 25,000 mice in some 72 different treatment groups at 7 dose levels. The desired end-product of the center is to produce a series of tests which can be done quickly, efficiently, and economically and allow for a realistic estimate of risk to man of suspected toxic chemicals.

Analysis of chlorinated insecticides and congeners.

A review on the state-of-the-art for analysis of chlorinated insecticides and their congeners is presented. Tables are included that show comparisons among gas chromatographic systems, high speed liquid chromatographic systems and sample preparation methods as well as an overview on sample cleanup.