The frequency and mutational profile of H-ras gene activation were determined in spontaneous liver tumors of male C57BL/6 x C3H/He mice and in tumors induced with the genotoxic hepatocarcinogen benzidine-2 HC1 or the nongenotoxic hepatocarcinogens phénobarbital, chlo roform, and ciprofibrate. DNA sequence analysis of the 11-ras gene from representative tumors revealed that 32 of 50 (64%) spontaneous tumors and 13 of 22 (59%) benzidine-2 HCl-induced tumors contained a point mutation in codon 61. Tumors induced with the nongenotoxic agents had a much lower frequency of codon 61 mutations, i.e., phénobarbital,1 of 15 (7%); chloroform, 5 of 24 (21%), and ciprofibrate, 8 of 39 (21%). No mutations were observed at codons 12, 13, and 117 in tumors from any of the groups. Only three base pair substitutions within codon 61 were found. The one most frequently detected in all of the groups was a C-G lo A I transversion at the first nucleotide position, occurring at a 59%, 85%, 100%, 80%, and 88% frequency in the spontaneous tumors and in the tumors induced with benzidine 2-HC1, phénobarbital,chloroform, and ciprofibrate, respectively. In these same groups an Al to G-C transition or an A • T to T • A transversion at the second nucleotide position occurred at a frequency of 34%, 8%, 0%, 0%, and 12%, and 6%, 8%, 0%, 20%, and 0%, respectively. The number of tumors carrying an activated H-ras gene in the nongenotoxic treatment groups is within the range that would be expected if those animals had not received any treatment. This indicates that the activation of the H-ras gene in those tumors is probably the result of a spontaneous event. The data suggest that these toxicologically and pharmacologically diverse nongenotoxic hepatocarcinogens increase the frequency of liver tumors but do not induce mutations in the H-ras gene. Instead these agents appear to interact with a population of cells that do not contain an activated H-ras gene. This suggests that the mechanisms of tumor development by these nongenotoxic carcinogens differ at least partially from the mechanisms responsible for the development of spontaneous tumors or those induced by a typical genotoxic agent.

The mechanisms of stress-related immune alterations have not been fully elucidated. Cell-mediated immune responses as well as antibody and certain cytokines are reported as being suppressed during times of high stress. However, the role of suppression vs dysregulation has not been established in human stress models. The effect of exam stress on regulatory cytokines in 16 healthy medical students was assessed by measuring type-1 (IFN-γ) and type-2 (IL-10) cytokines from 72-h PHA/PMA-stimulated PBMC 4 weeks before and 48 h after exams. Results demonstrated decreased IFN-γ accompanied by increased IL-10 during exam stress that resulted in a decreased IFN-γ:IL-10 ratio. There was a significant correlation between the cytokine response to PHA/PMA and number and subjective adjustment to daily hassles. Additionally, students who reported greater levels of loneliness also reported greater numbers of and poorer subjective adjustment to hassles. The differences were consistent in both males and females but did not correlate with AM cortisol levels. Additionally, when individuals were grouped into high vs low preexam hassle levels, the type-1/type-2 shift in the IFN-γ:IL-10 ratio occurred in the low hassles group only. These data suggest that psychologically stressful situations shift type-1/type-2 cytokine balance toward type-2 and result in an immune dysregulation rather than overall immunosuppression. This may partially explain the increased incidence of type-2-mediated conditions such as increased viral infections, latent viral expression, allergic/asthmatic reactions, and autoimmunity reported during periods of high stress.

There is increasing concern that birds in terrestrial ecosystems may be exposed to spent lead shot. Evidence exists that upland birds, particularly mourning doves ( Zenaida macroura ), ingest spent lead shot and that raptors ingest lead shot by consuming wounded game. Mortality, neurological dysfunction, immune suppression, and reproductive impairment are documented effects of exposure to lead in birds. An ecological risk assessment on the impact of lead shot exposure in upland birds was conducted and is presented in the context of the new United States Environmental Protection Agency's Ecological Risk Assessment Paradigm. A considerable amount of spent lead shot is released into the environment each year from shooting and hunting. Doves collected from fields that are cultivated to attract mourning doves for hunting activities show evidence of ingestion of spent lead shot. Because lead can cause both acute and chronic toxicity if ingested by birds, and because there is evidence of widespread deposition of lead shot in terrestrial ecosystems, concern for impacts on upland game birds and raptors seems warranted. Although this ecological risk assessment does not clearly define a significant risk of lead shot exposure to upland game birds, this issue merits continued scrutiny to protect our upland game bird and raptor resources.

Immunotoxicology is a relatively new field of investigation and is becoming recognized and used by toxicologists involved in drug and chemical testing. The purpose of this study was to evaluate the enzyme-linked immunosorbent assay (ELISA) as a means of quantitating humoral immune responses in rats exposed to immunomodulating chemicals. The ELISA proved to be highly sensitive and quantitative, simple to perform, and reliable. The assay is also economically feasible and automated so that large numbers of samples can be analyzed at one time. The antigen used in the study was bovine serum albumin, and the immunosuppressive chemicals used to validate the system were lead, polychlorinated biphenyl, cyclophosphamide, and dexamethasone. Practical application of the procedure to immunotoxicology testing is discussed.