Conservation Values and Risk of Handling Bats: Implications for One Health Communication.

Flying-foxes provide critical ecosystem services, but their role as hosts to zoonotic pathogens may undermine conservation support. We surveyed 214 residents of Cairns, Australia, regarding their perceptions about health risks associated with flying-foxes and support for flying-fox conservation. Greater likelihood of handling a flying-fox was associated with lower knowledge about risks, greater conservation support, and environmental organization membership. Respondents less likely to seek medical attention after a minor scratch tended to be younger, unemployed and perceive lower risk. Individuals who support flying-fox conservation should be one group targeted in One Health communication integrating health and conservation messages.

Health advocacy: a vital step in attaining human rights for adults with intellectual disability.

BACKGROUND: People with intellectual disability (ID) experience health inequity compared with the general population, a key contributing factor being disparities in social determinants of health. The enactment of the United Nations Convention on the Rights of Persons with Disabilities (CRPD) provides a platform for the progression and promotion of health and other interconnected rights to address barriers to the highest attainable standard of health for this populace. Rights can be brought to life through advocacy efforts. This paper explores the meaning, perceptions and experiences of advocacy by family members and paid support workers of adults with ID and locates the findings within a health and human rights discourse. METHODS: As part of a larger randomised controlled trial, 113 parents and 84 support workers of adults with ID completed a telephone interview that included open-ended questions about their understanding and experiences of advocacy. Thematic analysis was used to identify relevant themes. RESULTS: Five key themes were identified. The first underscored how advocacy to 'speak up' for the person with ID is integral to both parent and support worker roles. The second and third themes considered the contexts for advocacy efforts. Access to quality health care was a core concern, along with advocacy across other areas and sectors to address the person's wider psychosocial needs. The remaining themes highlighted the many dimensions to advocacy, including differences between parent and support worker views, with parental advocacy being an expression of 'caring' and support workers motivated by a 'duty of care' to protect the individual's 'rights'. CONCLUSION: Parent and support worker advocacy provides one means to address the social determinants of health and fulfilment of health rights of and for people with ID. Policy and practice in the context of governmental obligation under the CRPD should support advocacy and make health rights the reality not rhetoric for this group of men and women.

The effect on human sex ratio at birth by assisted reproductive technology (ART) procedures--an assessment of babies born following single embryo transfers, Australia and New Zealand, 2002-2006.

OBJECTIVE: To assess the effect on the human sex ratio at birth by assisted reproductive technology (ART) procedures. DESIGN: Retrospective population-based study. SETTING: Fertility clinics in Australia and New Zealand. POPULATION: The study included 13,368 babies by 13,165 women who had a single embryo transfer (SET) between 2002 and 2006. METHODS: Logistic regression was used to model the effect on the sex ratio at birth of ART characteristics [in vitro fertilisation (IVF) or intracytoplasmic sperm insemination (ICSI) SET, cleavage-stage or blastocyst SET, and fresh or thawed SET] and biological characteristics (woman's and partner's age and cause of infertility). MAIN OUTCOME MEASURES: Proportion of male births. RESULTS: The crude sex ratio at birth was 51.3%. Individual ART procedures had a significant effect on the sex ratio at birth. More males were born following IVF SET (53.0%) than ICSI SET (50.0%), and following blastocyst SET (54.1%) than cleavage-stage SET (49.9%). For a specific ART regimen, IVF blastocyst SET produced more males (56.1%) and ICSI cleavage-stage SET produced fewer males (48.7%). CONCLUSIONS: The change in the sex ratio at birth of SET babies is associated with the ART regimen. The mechanism of these effects remains unclear. Fertility clinics and patients should be aware of the bias in the sex ratio at birth when using ART procedures.

ICCVAM evaluation of the murine local lymph node assay. Conclusions and recommendations of an independent scientific peer review panel.

The validation status of the murine local lymph node assay (LLNA), a method for assessing the allergic contact dermatitis potential of chemicals, was evaluated by an independent peer review panel (Panel) convened by the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM). The LLNA measures lymphocyte proliferation using incorporation of radioactive thymidine or iododeoxyuridine into cells of the draining lymph nodes of mice topically exposed to a test article. The Panel concluded that the assay performed as well as currently accepted guinea pig methods [guinea pig maximization test (GPMT)/Buehler assay (BA)] for the hazard identification of strong to moderate chemical sensitizing agents, but that it might not correctly identify all weak sensitizers or metals (potential false negative response) or all strong irritants (potential false positive response). The Panel concluded also that the LLNA involves less pain and distress than conventional guinea pig methods. The Panel unanimously recommended the LLNA as a stand-alone alternative for contact sensitization hazard assessment, provided that certain protocol modifications were made. These included collection of individual, rather than pooled, animal response data; the inclusion of a concurrent positive control; and consideration of dose-response information and statistical analyses. A standardized LLNA protocol is provided.

Immunotoxicology assessment in the pharmaceutical industry.

Through several inter-laboratory evaluation studies, selected methods were optimized and evaluated using reference compounds in rodents, to determine their predictive value for detecting toxicity to the immune system. These provide the basis for the OECD, EPA and pending FDA Guidelines. To describe the status of immunotoxicity evaluation using these methods in the pharmaceutical industry, a survey was conducted, and is reported, of ongoing activities among the major pharmaceutical companies. The results describe which assays are performed, how compounds are selected for evaluation; and when, during the drug development process, an evaluation is performed. Finally, the strategy at Sanofi, for the evaluation and application of immunotoxicity methods during the preclinical development of new molecular entities (NMEs) is described. During the past 8 years, Sanofi has evaluated more than 27 NMEs from multiple therapeutic classes as well as four reference compounds (azathioprine, dexamethasone, cyclophosphamide and cyclosporin A). Our experience with multiple animal species (rat, dog and monkey) and immunotoxicity assays selected from the recommended tiers as well as the outcome from the evaluation of our NMEs and reference standards, is described. This experience has led us to believe that immunotoxicology parameters represent an important adjunct for the safety assessment of NMEs. In addition, these methods were easily integrated into the drug development process and yielded an unexpectedly low frequency of positive results. In summary, immunotoxicity can be evaluated on a case-by-case basis driven by pathology or clinical hematology findings, by the drug's indication, the chemical class or indication of the NME evaluated (for example, anti-viral agents), or systematically performed.

Issues with introducing new immunotoxicology methods into the safety assessment of pharmaceuticals.

Unfortunately, the principal routine toxicology methods employed for the safety assessment of new products are over 40 years old and rely primarily on histopathological evaluation. It is difficult to introduce newer immunotoxicology or molecular toxicology methods into toxicity assessment without extensive and time consuming validation requiring several years due to concern for standardization of methods, inter-laboratory replication of these methods and resistance to acceptance of new methods by both regulatory agencies and industry. During the past 15 years, significant progress has occurred in the fields of molecular biology and basic/clinical immunology which promoted the establishment of newer more sensitive methods to assess cell injury or immune system effects in humans and laboratory animals. This brings us to the challenges associated with trying to introduce new immunotoxicology or molecular toxicology methods into the safety assessment of new products. Our experience at Sanofi Research with immunotoxicity methods development or validation and approaches for molecular toxicology and their application to the preclinical development of new chemical drug entities (NCE) will be discussed. Laboratories to investigate immunotoxicity and molecular toxicology were established during the past 10 years among several industrial research groups for the evaluation of new chemicals and drug candidates. Immunotoxicology methods have been selected and optimized for rodent testing leading to four inter-laboratory collaborative studies to demonstrate the reproducibility and value of these methods for predicting toxicity. Our experience at Sanofi has led us to believe that these newer methods can represent an important part of drug development, should be applied on an as needed basis, and should be driven by data suggestive of an immune or molecular toxicology effect or by the class of the chemical being evaluated. Ex vivo and in vitro assays are selected from a menu of validated methods for application on a case-by-case basis. Results in this area with inter-laboratory validation of these methods will be discussed. Newer molecular toxicology and immunotoxicity methods are beginning to play a more important role in the safety evaluation and risk assessment process.

The impact of prenatal diagnosis on NTD surveillance.

Active and passive surveillance methods were utilized in an attempt to identify all neural tube defect (NTD)-affected pregnancies in South Carolina, a state previously identified to have a high prevalence of these defects (Greenberg et al., 1983). Sources of case ascertainment included maternal serum alpha-fetoprotein (MSAFP) programmes, prenatal diagnosis (amniocentesis) programmes, physician offices, perinatal centres, hospital medical record departments, and vital records. One hundred and nine NTD cases were identified over 24 months, indicating a prevalence of 1.60 cases per 1000 recorded births and fetal deaths (surveillance 1 October 1992-30 September 1994). Fifty-three (49 per cent) of the 109 NTD-affected pregnancies were either spontaneously or electively aborted prior to 26 weeks' gestation. Only three (6 per cent) of these early termination NTD cases were recorded in vital records, while medical records recorded 40 cases (75 per cent). By monitoring MSAFP programmes and maintaining frequent contact with physician offices and perinatal centres, 85 per cent of these early termination NTD-affected pregnancies were identified. However, for complete ascertainment of NTD-affected pregnancies, the utilization of all of these ascertainment methods was necessary, as each ascertainment method identified NTD cases missed by the other methods. Consideration of the significant impact of prenatal diagnosis on NTD surveillance and the use of multiple ascertainment methods in an attempt at complete ascertainment is particularly important now because of the recent recommendation for the periconceptional use of folic acid to prevent neural tube defects and the need for epidemiological studies to monitor the effectiveness of this prevention.

Surveillance for anencephaly and spina bifida and the impact of prenatal diagnosis--United States, 1985-1994.

PROBLEM/CONDITION: The reported prevalence of anencephaly and spina bifida in the United States has steadily declined since the late 1960s. During this time, the ability to diagnose these defects prenatally has progressed rapidly. Many U.S. birth defects surveillance systems ascertain defects only among live-born infants or among infants and fetuses beyond a certain gestational age, thus excluding defects among pregnancies prenatally diagnosed as being affected by a neural tube defect (NTD) and electively terminated before the gestational age limit. The impact of prenatal diagnosis and subsequent pregnancy termination on the reported prevalence of anencephaly and spina bifida in the United States has not been well established. However, assessment of this impact is crucial to the use of surveillance data to monitor trends in the occurrence of NTDs and the effectiveness of interventions for these defects (e.g., increased consumption of folic acid). REPORTING PERIOD: This report presents data from birth defects surveillance systems in six states over different time periods: Arkansas, 1985-1989; California, 1989-1991; Georgia, 1990-1991; Hawaii, 1988-1994; Iowa, 1985-1990; and South Carolina, 1992-1993. DESCRIPTION OF SYSTEMS: Population-based data about a) live-born and stillborn infants with anencephaly and spina bifida and b) pregnancies electively terminated after prenatal diagnosis of these defects were analyzed from the Arkansas Reproductive Health Monitoring System; the California Birth Defects Monitoring Program; CDC's Metropolitan Atlanta Congenital Defects Program; the Iowa Birth Defects Registry, the University of Iowa, and the Iowa Department of Public Health; and the Greenwood Genetic Center in South Carolina. Data also were analyzed from the Hawaii Birth Defects Monitoring Program, which includes data for some women who were not residents of the state. The systems differed in the size and racial/ethnic composition of the populations studied, the surveillance methods used, the completeness of ascertainment, and the availability and utilization of prenatal testing and pregnancy termination. RESULTS AND INTERPRETATION: Among all pregnancies ascertained in which the infant or fetus had anencephaly or spina bifida, the percentages that were electively terminated ranged from 9% in Arkansas to 42% in Atlanta and Hawaii, with a corresponding increase in the adjusted prevalence of these defects compared with the prevalence at birth. In each system, pregnancies associated with anencephaly were terminated more frequently than were those associated with spina bifida. These data indicate that the impact of prenatal diagnosis and subsequent pregnancy termination on the prevalence at birth of anencephaly and spina bifida differs among geographic areas and populations. Comprehensive surveillance for these defects requires inclusion of pregnancies that are prenatally diagnosed and then terminated. ACTIONS TAKEN: CDC will use these data to promote the inclusion of prenatally diagnosed and terminated pregnancies in estimates of the prevalence of anencephaly and spina bifida generated by birth defects surveillance programs in the United States. Including such pregnancies is crucial to the ability of these programs to monitor trends accurately and to establish the effectiveness of interventions, including the use of folic acid, for these defects.

Immunotoxicology: An overview.

Significant progress has occurred in the fields of basic and clinical immunology over the past 15 years, leading to the establishment and validation of sensitive methods for assessing immune system changes in humans as well as laboratory animals. Concern over the potential toxic effects of chemicals and certain drugs on the immune system prompted the application of these methods to assess the safety evaluation of the immune system and the establishment of the subdiscipline of immunotoxicology within toxicology. Methods have been selected and optimized for rodent testing, which have led to national and international comparative studies to demonstrate the reproducibility and utility of these methods for predicting immune system effects. Laboratories for the investigation of immunotoxicity have, likewise, been established during the past 10 years among industrial research groups for the evaluation of new chemicals and drug candidates. 6 years ago, Sterling Winthrop Inc. established an immunotoxicology laboratory dedicated to drug discovery and development effort. Experience has demonstrated that immunotoxicological assessment can represent an important aspect of any drug safety evaluation, and need not be a routine screening procedure, but should be driven by data suggestive of an immune system effect or concern over the chemical class of the agent. Assays for the evaluation are selected from a menu of validated methods on a case-by-case basis. Immunotoxicology will continue to play a more significant role in the safety and risk assessment process, because of the pivotal role of the immune system in host defence. This overview describes the structure, organization and function of the immune system, and experience with immunological methods development, application to and experience in the preclinical development of new chemical drug entities and in vitro applications.

The integration of immunotoxicology in drug discovery and development: Investigative and in vitro possibilities.

The development of new pharmaceuticals requires a tremendous investment of time and resources. The early integration of investigative toxicology studies and new toxicological methods, such as immunotoxicological studies, into the selection of new drug candidates facilities compound safety evaluation, reduces risk, and improves development cycle time. Experience at Sterling Winthrop Inc. has led us to believe that immunotoxicology assessment represents an important and useful tool in drug discovery and development, but that it should not be applied as a routine screening procedure. Instead, immunotoxicity evaluation should be initiated as a response to knowledge about the class of drug under investigation, or when data from other studies suggest an effect on the immune system. Three examples of this approach are given and each one demonstrates the potential of in vitro immunotoxicology assays to reduce the time, resources and animal use required in the discovery and development of new drug candidates.

Summary of an international methods validation study, carried out in nine laboratories, on the immunological assessment of cyclosporin A in the Fischer 344 rat.

In evaluating the adverse effects of chemicals on the immune response, the mouse has been the predominant animal species of choice. The acceptance of the mouse as a validated animal model has been the result, in part, of the studies conducted by the US National Toxicology Program (NTP). In these studies functional and host-resistance assays were developed and validated using five compounds and four testing laboratories. In toxicological evaluations of drugs and chemicals, the rat has been the rodent species of choice of the worldwide toxicology community. The current study was designed to begin the validation of the rat as a model for immunotoxicology assessment. Nine laboratories participated in the study, including laboratories from Canada, France, the United States and The Netherlands. Before the study began a detailed protocol was prepared and standard operating procedures were developed. Cyclosporin A was selected as the prototype immunosuppressive compound, and was administered orally to male Fischer 344 rats. Data were collected on standardized forms and submitted to a central laboratory for statistical analysis. Similar dose-response trends were observed between the various laboratories. In the natural killer cell assay and concanavalin A mitogen assay similar results were observed in at least 63% of the laboratories. In the T-dependent antibody-plaque forming cell assay, and the mixed leucocyte response, 100% of the laboratories that conducted the assays had statistically similar results. The results from this study support the usefulness of the rat as a model species for immunotoxicity assessment and represent a beginning for international interlaboratory validation of immunotoxicology assays in this species.

The integration of investigative toxicology in the drug discovery process.

Integrating toxicology early in the drug discovery process adds value by providing the earliest possible identification of a compound's potential for toxicological and pathological effects relevant to intended clinical use. With this approach true 'lead' candidates, with a high probability of clinical success, are identified and advanced while reducing effort and resources expended on compounds without the requisite therapeutic index. Resources are focussed on the speed of getting a discovery 'lead' into early clinical development, defining the mechanisms of observed preclinical toxicity and their relevance to human use, and developing early safety data with in vitro test systems ahead of in vivo systems where possible, thus reducing animal use.

Clinical pathologic alterations associated with subcutaneous administration of recombinant human interleukin-4 to cynomolgus monkeys.

Recombinant human interleukin 4 (rhuIL-4) is a candidate for the treatment of refractory cancer based on its potential to enhance immune function. Recombinant human IL-4 was administered subcutaneously at 0, 1, 5, or 25 micrograms/kg/day for 28 days with a 14-day recovery to male and female cynomolgus monkeys as part of the preclinical safety evaluation. Clinical pathologic changes related to treatment with rhuIL-4 were evidence of consumptive coagulopathy, erythrocyte fragmentation, lymphocytosis, and lymphocyte morphologic changes indicative of marked antigenic or mitogenic stimulation, mild eosinophilia and neutrophilia, hypoalbuminemia, hypocholesterolemia, and hypertriglyceridemia. Based on data obtained after the 14-day recovery period, the clinical pathologic changes associated with rhuIL-4 administration were considered to be reversible.

Preclinical evaluation of recombinant human interleukin-4.

Recombinant human IL-4 (rhuIL-4) is primate-specific and produces multiple biologic effects on lymphoid cells involved in protection against cancer. RhuIL-4 was evaluated in the cynomolgus monkey to support clinical studies for the immunotherapy of cancer. Administration of rhuIL-4 to monkeys by SC injection of 0, 0.5, 2.5 or 12.5 micrograms/kg BID for one-month (with two-week recovery) resulted in alterations in clinical chemistry and hematology (CCH) parameters consistent with a consumptive coagulopathy. Histomorphologic evaluation revealed increased granulopoiesis, testicular atrophy, and proliferative and inflammatory vascular lesions (VL). IVL principally affected the arterial tree with some proliferation of medial smooth muscle. During the latter part of the treatment and recovery period. CCH parameters approached or returned to pretreatment values, the former finding attributed to the production of antibody to rhuIL-4. At final necropsy, bone marrow appeared normal, and IVL decreased in incidence and severity. ELISA studies of serum indicated 50-90% of the monkeys developed antibody titers > 1000 by Day 22 (not observed in man). The frequency and severity of adverse effects due to rhuIL-4 in the clinic appear to be does-related and reversible with few objective responses to therapy observed. Common toxicities included milk to moderated fever and fatigue and an occasional change in hematopoietic, hepatic and renal function. The monkey predicted hematologic findings, but not all target organ effects.

Correlation between chemical suppression of natural killer cell activity in mice and susceptibility to cytomegalovirus: rationale for applying murine cytomegalovirus as a host resistance model and for interpreting immunotoxicity testing in terms of risk of disease.

The purpose of this study was to determine the relationship between chemical suppression of natural killer (NK) cell activity in mice and chemical effects on susceptibility to murine cytomegalovirus (MCMV) infection. The goal was to provide a rational basis for applying MCMV as a host resistance model for immunotoxicity testing and to provide risk assessors some guidance in relating suppression of NK cell activity to enhanced risk of disease. Data from studies with eight chemicals administered in various doses and by various routes were evaluated, and a significant correlation was observed between chemical suppression of virus-augmented NK cell activity and increased mortality due to MCMV infection. In contrast, effects of the same chemical treatments on spontaneous NK cell activity (i.e., basal activity in uninfected mice) did not correlate with effects of these chemicals on mortality due to MCMV. Although chemicals that suppressed spontaneous NK cell activity enhanced infection, the converse was not always true--that is, increased susceptibility to infection and suppression of virus-augmented NK cell activity were observed on three occasions when spontaneous NK cell activity was unaffected. This latter phenomenon plus the fact that for two chemicals spontaneous NK was suppressed at concentrations twofold below that which affected mortality appear to account for the poor statistical correlation. Nevertheless, the data indicate that MCMV is a useful host resistance model to be applied in immunotoxicity testing when suppression of NK cell activity has been demonstrated. However, virus-augmented activity may be a better indicator than spontaneous activity. The data also indicated that suppression of NK cell activity is predictive of increased susceptibility to infection and hence provides qualitative guidance (hazard identification) to risk assessors.

Subchronic oral and intravenous (i.v.) safety evaluation and pharmacokinetics in rats and dogs of ipazilide fumarate (Win 54, 177-4), an antiarrhythmic agent.

Ipazilide fumarate (Win 54, 177-4) is a chemically novel antiarrhythmic agent that prolongs ventricular refractoriness and possesses antiectopic activity. Subchronic (29 days) nonclinical safety evaluation of ipazilide was conducted following oral and iv administration in Sprague-Dawley rats (20-320 mg/kg oral and 1.25-10 mg/kg iv) and 14 and 28 days in beagle dogs (3-30 mg/kg oral and 2.5-20 mg/kg iv). The pharmacokinetic parameters of ipazilide indicate that ipazilide is absorbed (tmax less than or equal to 1 hr) in fasted rats and dogs following single and repeated oral administrations. The apparent elimination half-life in the two species is approximately 1 hr (except in rats at a dosage of 320 mg/kg), suggesting rapid clearance. Increases in liver weights (rats 320 mg/kg) accompanied by the observation of centrilobular hypertrophy of hepatocytes were considered an expression of an adaptive metabolic response of the liver to ipazilide and may be associated with the induction of microsomal enzymes. Duodenal villous atrophy and epithelial hyperplasia (rats, 80 and 320 mg/kg) were interpreted to represent an irritant response to the drug. Local irritation was also observed at the injection site in rats and dogs. Dogs tolerated the oral and the iv administration of ipazilide at dosages of up to 30 and 20 mg/kg, respectively. Despite emesis (oral dogs), which was reduced in frequency following repeated treatment over several weeks, plasma levels in treated dogs (i.e., Cmax 4-5 micrograms/ml) were approximately twice that required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre-clinical toxicity of IL-4: a model for studying protein therapeutics.

The purpose of this presentation was to review issues and findings in the pre-clinical development and evaluation of recombinant human protein therapeutics. Since human cytokines and lymphokines are endogenous proteins, their pre-clinical development and evaluation would seem straightforward and their toxicities minimal. Unfortunately, the pre-clinical development of this class of agents has been problematic and confounding. Some of the clinical toxicities and pharmacodynamics have been predicted by the pre-clinical evaluation and others have not. Some molecules are species specific which limits species selection for pre-clinical evaluation. Other confounding issues include: route of exposure, synergy of toxicity with other lymphokines, length of study design, immunogenicity, predictiveness of pre-clinical evaluation and iatrogenic toxicities. An approach used by SWPRD in the evaluation of this class of molecules was discussed. Insight gained during the pre-clinical and clinical development of these molecules should simplify the further development of protein therapeutics that follow. Specific studies with recombinant human interleukin-4 (rhuIL-4) were reviewed in detail as part of a pre-clinical safety evaluation. Native IL-4 has properties that exemplify many of the immune recognition-induced lymphokines and is produced principally by activated T-lymphocytes CD4+. It is a co-factor in B-cell proliferation and enhances ex vivo B-cell expansion and is believed to be a candidate for the treatment of refractory cancer based on this immune enhancement ability. rhuIL-4 is a 15,400 molecular weight cytokine produced in a yeast expression system.(ABSTRACT TRUNCATED AT 250 WORDS)

Examination of immune parameters and host resistance mechanisms in B6C3F1 mice following adult exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Adult female B6C3F1 mice were given a single ip dose of 0, 01, 1.0, or 10.0 micrograms/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and examined for immune function and host resistance 7-10 d later. Exposure to TCDD resulted in a significant dose-related decrease in induction of both IgM and IgG antibody-forming cells. This suppression was noted for both T-dependent and T-independent antigens. TCDD at a dosage of 10 micrograms/kg was shown to suppress production of antibody to viral hemagglutinin. In contrast, TCDD exposure had no significant effect on natural killer cell function, production of interferon, or various parameters of macrophage function. Assessment of host resistance revealed a significant increase in susceptibility to fatal infection with influenza virus, but no significant alteration in susceptibility to infection with the bacterium Listeria monocytogenes.

Molecular mechanism of 7,12-dimethylbenz[a]anthracene-induced immunosuppression: evidence for action via the interleukin-2 pathway.

Previous studies in this laboratory have demonstrated that exposure of mice to the carcinogenic polycyclic aromatic hydrocarbon 7,12-dimethylbenz[a]anthracene results in suppression of both humoral and cell-mediated immunity. This suppression is unaccompanied by any significant alteration in splenic lymphocyte subpopulation composition, suggesting that the immune deficit was due to a modulation of lymphocyte function. Additional studies implicated the T helper lymphocyte as the probable target for 7,12-dimethylbenz[a]anthracene-induced immunosuppression, apparently through an inhibition of interleukin 2 production. The purpose of the present study was to examine the mechanism of 7,12-dimethylbenz[a]anthracene-induced T lymphocyte dysfunction at the molecular level and to determine the consequences of 7,12-dimethylbenz[a]anthracene exposure on the interleukin 2 pathway. In vitro exposure of Con A-activated splenocytes to 7,12-dimethylbenz[a]anthracene resulted in suppression of the mitogenic response, suppressed interleukin 2 production, and reduced the expression of the high affinity receptor for interleukin 2. In contrast, expression of the low affinity interleukin 2 receptor was not affected. In addition, interleukin 2-dependent lymphoblasts and long term cultured splenocytes exhibited a dose-dependent decrease in proliferation following in vitro exposure to 7,12-dimethylbenz[a]anthracene. These results suggest that 7,12-dimethylbenz[a]anthracene-induced immunosuppression may be mediated, at least in part, through the interleukin 2/interleukin 2 receptor pathway.