The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program (NTP). The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by the NTP on March 2009 (see http://ntp.niehs.nih.gov/ntp/htdocs/levels/09-3566%20NTP-ITOX-R1.pdf). The findings and conclusions for this study should not be construed to represent the views of the NTP or the US Government.
The Immunotoxicity of 2-Mercaptobenzothiazole
Contact Hypersensitivity Studies in Female B6C3F1 Mice
NTP Report Number: IMM90003
2-Mercaptobenzothiazole is used as an accelerator in the processing of rubber products. There are a number of reports indicating contact dermatitis associated with 2-mercapto- benzothiazole in humans following exposure to rubber (e.g., Correcher and Perez, Contact Derm. 7:275, 1981; Tosti et al., Contact Derm. 13:339, 1985; and Foussereau et al., Contact Derm. 14:233, 1986) as well as in animal models (e.g., Goodwin et al., Contact Derm. 7:248, 1981).
2-Mercaptobenzothiazole (Lot # V10-479/B01, ~96% pure as determined by HPLC) was obtained from the R. T. Vanderbilt Co., Inc. (Norwalk, CN) and was prepared in acetone. Primary irritancy studies indicated that concentrations of 2-mercaptobenzothiazole up to 7.5% were non-irritating, which was the highest concentration which remained soluble at room temperature. Female B6C3F1 mice were sensitized dermally to either 0, 1%, 3%, or 7.5% 2-mercaptobenzothiazole for 5 consecutive days and challenged 7 days later with a 7.5% solution. Site preparation included dermabrasion as well as intradermal injection of Freund's complete adjuvant in some mice. A 0.5% solution of 1-fluoro-2,4- dinitrobenzene (DNFB; Sigma Chem. Corp.; Lot No. 88F-3833; > 99% pure as determined by HPLC) was used as a positive control. The mice were divided into 10 treatment groups of 8 mice/group as shown in Table 1. The irritancy response was determined by monitoring the extravasation of 125I-bovine serum albumin into the treated area. The contact hypersensitivity response was determined by monitoring the infiltration of 125I-iododeoxyuridine labeled cells into the challenge site and the mouse ear swelling test (MEST).
A hypersensitivity response was observed in B6C3F1 female mice sensitized with 2-mercaptobenzothiazole, without pretreatment with adjuvant, when the mice were tested by the MEST 2 days after sensitization, but not after 1 day (data not shown). No statistically significant or dose-related response could be detected with the radioisotopic assay following challenge, with or without adjuvant.
Under these experimental conditions, a statistically significant contact hypersensitivity response to 2-mercaptobenzothiazole was observed in mice when the site of sensitization was prepared by shaving and dermabrasion without adjuvant. For unknown reasons, the response was detected by the MEST, but not by the radioisotopic assay.
Table 1. Study Design: Contact Hypersensitivity Study with 2-Mercaptobenzothiazole
|2 (8)||Baseline Control||+||Vehicle||7.5% MBT|
|3 (8)||Experimental||+||1% MBT||7.5% MBT|
|4 (8)||Experimental||+||3% MBT||7.5% MBT|
|5 (8)||Experimental||+||7.5% MBT||7.5% MBT|
|6 (8)||DNFB Positive Control||-||0.5% DNFB||0.5% DNFB|
|7 (8)||DNFB Negative Control||-||Vehicle||0.5% DNFB|
|8 (8)||Baseline Control||-||Vehicle||7.5% MBT|
|9 (8)||Experimental||-||3% MBT||7.5% MBT|
|10 (8)||Experimental||-||7.5% MBT||7.5% MBT|
note: MBT = 2-mercaptobenzothiazole; FCA = Freund's complete adjuvant; DNFB = 1-fluoro-2,4-dinitrobenzene