5-amino-o-cresol

Immunotoxicity

Description of key information

According the results of the key studies (Klimisch 2), the registered substance 4-amino-2-hydroxytoluene can inhibit the mixed lymphocyte reaction. Hence, the No observe Adverse Effect was defined as below 10 µg/mL for lymphocyte culture (in vitro method) and above 120 mg/kg bw/day on rabbit for the immunosuppresive property (high dose level used in the study) .

Key value for chemical safety assessment

Effect on immunotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

120 mg/kg bw/day

Study duration:

subacute

Species:

rabbit

Additional information

In thein vivostudy, the capacity of the test substance 5-amino-o-cresol to suppress humoral immuno­logical responses was investigated by studying their ability to: inhibit the production of circulating antibodies to sheep red blood cells by rabbits. Animals receiving the test substance showed a very slight reduction in antibody production. However, a comparison of the haemagglutinin response in the animals dosed with test substance, negative control animals and positive control animals (azathioprine) indicated that at no time did any of the test substance, 5-amino-0-cresol, induce the degree of immunosuppresssion exhibited by animals treated with azathioprine.Azathioprine, a well known immunosuppressive agent was used as a positive control and was found to suppress both humoral and cellular responses.

The second study was performed on lymphocytes cultures. The capacity of 5-amino-o-cresol to suppress cellular immuno­logical responses was investigated by studying their ability to inhibit the mixed lymphocyte culture response using lymphocytes from non-compatible primates. The toxic action of the test compounds on the lymphocytes in culture was assessed using the trypan blue dye exclusion technique. Leucocytes( final concentration of 1.0E6 cells/ml) were incubated with various concentrations of the chemicals for 5 days at 37°C. Trypan blue was then added to the cultures to give a final concentration of 0.1% and the cultures incubated for a further 10 minutes. The number of dead cells (those that had been stained with trypan blue) was estimated with a haemacytonter and the percentage of viable cells at each concentration of test compound was calculated. The cultures were then incubated for 4 days at 37C after which time they were radioactively labelled by the addition of 10 ul of RPM 1640 medium containing [3H-methyl] thymidine at a concentration of 20 uCi/ml. After a further 24 hours incubation at 37C, the suspensions were cooled and centrifuged. For the first experiment those levels of azathioprine 50, 25 and 10 ug/ml were used. The results showed that optimal suppression without toxicity was given by 10 ug/ml, and this level alone was used in subsequent tests. The test substace inhibited the mixed lymphocyte reaction. Azathioprine, a well known immunosuppressive agent was used as a positive control and was found to suppress the cellular response.

Justification for classification or non-classification

According the results of the key studies (Klimisch 2), the registered substance 4-amino-2-hydroxytoluene can inhibit the mixed lymphocyte reaction. Hence, the No observe Adverse Effect was defined as below 10 µg/mL for lymphocyte culture (in vitromethod) and above 120 mg/kg bw/day on rabbit for the immunosuppresive property (high dose level used in the study) .