Hexachlorobenzene-induced immunomodulation and skin and lung lesions: a comparison between brown Norway, Lewis, and Wistar rats.

Strain dependence of the induction of skin and lung lesions by hexachlorobenzene (HCB) in the rat was studied to further the insight into the etiology of the lesions. To this end, 3- to 4-week-old female Brown Norway (BN), Lewis, and Wistar rats received diets supplemented with 150 mg (BN and Lewis), 450 mg (BN, Lewis, and Wistar) or 900 mg (BN and Wistar) HCB per kilogram diet for 4 weeks. Gross skin lesion development during exposure as well as pathologic changes in skin and lungs and various parameters of immunomodulation after exposure were assessed. General toxicity as judged by a slight increase in body weight gain and induction of liver cell hypertrophy was similar in BN and Lewis rats exposed to 450 mg/kg HCB and in Wistar rats exposed to 900 mg/kg HCB. Skin lesions ranged from redness to large exudating sores with crusts. With regard to dose, time of onset, incidence, and severity, skin lesions were very severe in BN, moderate in Lewis, and negligible in Wistar. Porphyrins could not be detected in the skin, whereas porphyrins in the liver were seen only in Lewis rats. Histology showed epidermal hyperplasia, deep dermal venules with activated endothelium, and deep dermal inflammatory infiltrates mainly consisting of eosinophilic granulocytes in BN and of mononuclear cells in Lewis and Wistar. Nonlesional skin of HCB-exposed rats showed very similar, though less prominent, changes. Lung pathology appeared negligibly strain-dependent; histology showed venules with an activated endothelium surrounded by a perivascular infiltrate as well as focal alveolar macrophage accumulations in all strains. Parameters of immunomodulation showed moderate strain dependence; relative spleen weights were dose-dependently increased in BN and Wistar and in the 450 mg/kg group in Lewis rats. BN rats showed a more marked splenomegaly than the other strains. Relative popliteal lymph node weights were increased significantly in BN and Lewis rats exposed to 450 mg/kg HCB. In all strains, HCB increased lymph node HEVs. Serum IgE and IgG levels were increased significantly in a dose-dependent way in BN rats only. Total serum IgM levels were elevated significantly in BN, Lewis, and Wistar rats that received 450 mg/kg and in Wistar rats that received 900 mg/kg HCB. Serum IgM levels against ssDNA were dose-dependently increased in all strains, being more marked in BN and Lewis than in Wistar rats. It is concluded that the HCB-induced inflammatory skin and lung pathologies have different etiology. Pronounced strain differences in the skin lesions suggest a specific involvement of the immune system. Skin lesions correlated significantly with all assessed parameters of immunomodulation in BN, with some in Lewis and with none in Wistar rats. No correlation was observed between the parameters of immunomodulation and lung lesions.

Hexachlorobenzene-induced eosinophilic and granulomatous lung inflammation is associated with in vivo airways hyperresponsiveness in the Brown Norway rat.

We investigated whether the eosinophilic and granulomatous lung pathology that develops in Brown Norway (BN/SsNOlaHsd) rats upon feeding hexachlorobenzene (HCB) is associated with nonspecific in vivo airways hyperresponsiveness (AHR) to methacholine. To this end, female BN/SsNOlaHsd rats were exposed to diets with no supplementation or diets supplemented with 450 mg HCB per kg feed. On days 7 or 21 of exposure in vivo airways hyperresponsiveness to increasing concentrations of methacholine was assessed both by whole body plethysmography and by visual scoring. In addition, lungs were lavaged to count and differentiate lavage cells, and skin and lungs were processed for histology. Lungs of the control rats showed some scattered microgranulomas and by 3 weeks of control diet some rats showed rather extensive granuloma formation and perivascular and peribronchiolar infiltration of eosinophils, as well as increased responsiveness to methacholine. Oral exposure to HCB for 7 days caused a moderate perivasculitis, but no increase of total serum IgE levels and no AHR to methacholine was found. Prolonged HCB exposure for 21 days resulted in severe and extensive eosinophilic and granulomatous lung inflammation, a threefold increase of total serum IgE levels, and marked cholinergic AHR in all rats. Correlation analysis revealed a significant relation between the AHR and lung inflammation, as judged by granuloma formation and increased numbers of eosinophilic granulocytes in the lung interstitium, particularly around the bronchi and bronchioli. No correlation was observed between serum IgE levels and AHR. Data suggest that HCB induces AHR by stimulating eosinophilic lung inflammation and that the preexistent microgranulomas may predispose to development of the HCB-induced lung pathology.

Intestinal T lymphocytes of different rat strains in immunotoxicity.

In order to study the intestinal mucosal immune cells, with emphasis on single T lymphocytes, an inventory was made of single and organized lymphocytes in the epithelium and lamina propria of the small intestines of untreated Wistar, Fischer 344, and Lewis rats. The single and organized lymphocytes were examined microscopically. In addition, the single lymphocytes in the epithelium (IEL) and lamina propria (LPL) were analyzed by flow cytometry. Next, the use of flow cytometry analysis was explored to detect changes in the IEL T-lymphocyte population in subacute oral studies with the immunomodulating agents azathioprine and hexachlorobenzene. Untreated random-bred Wistar rats exhibited a large interindividual variability in IEL composition, while the variability was small in inbred Fischer 344 and Lewis rats. The explorative study with the 2 model immunomodulating compounds demonstrated that hexachlorobenzene increased the number of intraepithelial T lymphocytes with CD8+ phenotype at the cost of T cells with CD4+ phenotype in Lewis rats. Azathioprine did not induce distinct effects on the percentages of IEL. The data indicate that the intraepithelial lymphocytes in the intestines are a potential target for orally administered immunomodulating compounds and should therefore receive more attention in toxicologic pathology studies.