Lymph node cell proliferation assay in guinea pigs for the assessment of sensitizing potentials of chemical compounds

Evaluation of cell proliferation in ear and lymph node using BrdU immunohistochemistry for mouse ear swelling test

The mouse ear swelling test (MEST) was developed as an alternative to guinea pig models for measuring the contact sensitization potential. However, the MEST relies on the quantitative measurement of ear swelling by micrometer as the means of determining the endpoint. The purpose of this study was to investigate the possibility of using cell proliferation in the ear and lymph node by bromodeoxyuridine (BrdU) immunohistochemistry as a reliable marker for MEST. Female Balb/c mice were treated by the topical application of various sensitizers, 2,4-dinitrochlorobenzene (DNCB), toluene diisocyanate (TDI) and α-hexylcinnamaldehyde (HCA) and an irritant, sodium lauryl sulfate (SLS) following the protocol of MEST. The proliferation of cells in the ear and auricular lymph node was analyzed by BrdU incorporations into cells. There were significant increases in the cell proliferations of the ear and auricular lymph node in mice treated with DNCB and TDI compared to the vehicle control. All allergens and the irritant were correctly identified by the MEST using BrdU immunohistochemistry of lymph node responses. The standard MEST assay showed positive results in the case of the strong sensitizers, DNCB and TDI. However, HCA and SLS were not correctly identified in the ear swelling assay. These results suggest that the measurement of cell proliferation in the auricular lymph node using BrdU immunohistochemistry could provide a reliable marker for MEST.

Kupffer cells from halothane-exposed guinea pigs carry trifluoroacetylated protein adducts

The anesthetic, halothane, is bioactivated by the liver cytochrome P450 system to trifluoroacetyl-chloride, which can readily acylate liver protein. Covalent binding of the trifluoroacetyl moiety may result in hapten formation leading to the induction of an immune response and ultimately halothane hepatitis. In this study the presence of trifluoroacetylated-protein adducts in Kupffer cells was investigated to learn how the immune system might come in contact with the proteins. Guinea pigs were exposed to 1.0% halothane, 40% oxygen for 4 h. Kupffer cells were isolated on days 1 through 9 post-exposure, by liver perfusion and purification by elutriation. Using gel electrophoresis and Western blotting techniques, it has been demonstrated that Kupffer cells obtained from halothane-treated guinea pigs, do carry trifluoroacetyl-protein adducts as recognized by an anti-trifluoroacetyl-rabbit serum albumin antibody. Apparent molecular weights of polypeptides bound by trifluoroacetyl were of a wide range, 25-152 kDa. Bands were most prominent in the larger Kupffer cells with more appearing at lower molecular weights. Trifluoroacetyl-protein adducts were not detected in lung, spleen, lymph node or peripheral blood macrophages. This work suggests a role for Kupffer cells in the presentation of altered proteins in the liver to cells of the immune system.

Demonstration of a cellular immune response in halothane-exposed guinea pigs

Halothane hepatitis is considered to be a result of an idiosyncratic autoimmune reaction brought about by the formation of neoantigens that have been generated by covalent binding of halothane biotransformation intermediates. The guinea pig is being examined as an animal model to investigate an immune-mediated mechanism for halothane hepatotoxicity. Male Hartley guinea pigs were exposed to 1% halothane/40% oxygen for 4 hr, three times with 40-day intervals. Kupffer cells and splenocytes were isolated from animals on various days after each halothane exposure. Splenocytes were cocultured in a lymphocyte transformation test with various concentrations of TFA(trifluoroacetylated)-antigens for 7 days and proliferation was measured by 3H-thymidine incorporation. In a second experiment, Kupffer cells were cocultured with autologous as well as allogeneic splenocytes with or without concanavalin A to determine whole cell sensitization and accessory function by Kupffer cells from treated animals. A 4-fold increase in splenocyte proliferation occurred in response to TFA-guinea pig albumin. No significant increase in proliferation could be detected with TFA-lysine or guinea pig albumin. A 14-fold increase in splenocyte proliferation also occurred in response to Kupffer cells from halothane-exposed animals. Autologous splenocytes demonstrated more of a response from treated versus control animals, indicating possible involvement of major histocompatibility complex II antigens. These results indicate recognition of TFA-antigens and Kupffer cells as antigen-presenting cells in halothane-exposed guinea pigs. This study provides good evidence that a cellular immune response is involved in the guinea pig after halothane exposure.

Improved ex vivo/in vitro lymph node cell proliferation assay in guinea pigs for a screening test of contact hypersensitivity of chemical compounds

Simple and efficient ex vivo/in vitro screening systems for contact allergens are developed for alternative to conventional animal tests. We have previously proposed an ex vivo/in vitro proliferation assay as a first stage screening method with advantages over existing alternatives, using lymph node cells (LNC) from sensitized guinea pigs of the Hartley strain. In this study, we have first confirmed, by histochemical analysis using in vivo bromodeoxyuridine (BrdU) and pyronin staining, that the ex vivo/in vitro LNC proliferation reflects in vivo response of lymph nodes to contact allergens. Furthermore, to improve the LNC assay, we then have investigated several experimental conditions for their influences on the LNC assay, demonstrating that, (1) the subscapular and the cervical LNC responded highly to contact allergens, (2) among three cervical lymph nodes the superficial dorsal cervical lymph nodes were the most reactive, (3) several vehicles alone used for animal sensitization exhibited little influence on the LNC proliferation, (4) employment of stimulation index offset the inter-batch fluctuation of the LNC proliferation in the control animals as baseline proliferation. Under optimized experimental conditions as above, experimentally determined stimulation indexes of several contact allergens correlated well with their sensitizing potential estimated by conventional animal tests. Therefore, the ex vivo/in vitro LNC proliferation assay should be a simple and efficient alternative to conventional guinea pig testings including the guinea pig maximization test (GPMT).

Local lymph node activation in rats after dermal application of the sensitizers 2,4-dinitrochlorobenzene and trimellitic anhydride

Five rat strains were compared for their performance in the local lymph node assay (LLNA), a promising test system for the identification of the skin-sensitizing potential of chemicals in the mouse. The contract sensitizer 2,4-dinitrochlorobenzene (DNCB) and the contact and respiratory sensitizer trimellitic anhydride (TMA) were used as model chemicals and responses in rats were compared with those in BALB/c mice. The chemicals were applied to the dorsum of both ears, once daily for three consecutive days; 2 days (mice) or 3 days (rats) thereafter, proliferating cells were labelled by i.p. injection of BrdU 2 hr before the animals were killed. Systemic effects were subsequently assessed by determination of spleen, liver and kidney weights, skin effects by determination of swelling and inflammatory cell infiltration of the ears, and immune effects by determination of weight and proliferative activity of the local lymph nodes (LLN). Following application (x 3) of DNCB or TMA, minor systemic effects were observed, as indicated by slightly elevated spleen and liver weights in a few rat strains and the mice. Skin effects, consisting of increased ear thickness and presence of mononuclear inflammatory cell infiltrates, were observed in all rat strains treated with DNCB or TMA, LLN weights had increased, as had the proliferative activity in these nodes. It was concluded that effects induced by DNCB and TMA in all five rat strains were comparable with those in mice.