Activation of T cells by dendritic cells exposed to a reference sensitizer: Towards a promising model to assess the allergenic potential of chemicals

BACKGROUND

Low molecular weight chemicals constitute one of the major causes of occupational allergies. European legislation on chemicals recommends limiting the use of in vivo models for assessing the sensitizing potential of chemicals, and encourages the development of integrated alternative methods. An in vitro mouse model of bone marrow-derived dendritic cells (BMDCs) that showed good accuracy (75%) and sensitivity (69%) has previously been developed to assess the sensitizing potential of chemicals.

OBJECTIVE

To assess the ability of BMDCs to activate T cells (TCs) in vitro.

METHODS

BMDCs pre-exposed to the reference sensitizer ammonium hexachloroplatinate (AHCP) were co-cultured with different subpopulations of TCs. TC activation was assessed by surface marker expression, proliferation, and cytokine release.

RESULTS

The results showed significant activation of TCs co-cultured with dendritic cells pre-exposed to AHCP as evaluated by CD124 expression, proliferation, and cytokine secretion. Moreover, the response of TCs appeared to be Th2-oriented. Naive TCs were shown to be involved in this response, and the removal of regulatory TCs did not improve the cell response.

CONCLUSIONS

The BMDCs used in this previously developed model appear to have the ability to activate TCs, confirming that the BMDC model represents a reliable assay for assessing the sensitizing potential of chemicals.

Skin sensitization

Skin sensitization associated with allergic contact dermatitis is a common health problem and is an important consideration for toxicologists in safety assessment. Historically, in vivo predictive tests have been used with good success to identify substances that have the potential to induce skin sensitization, and these tests formed the basis of safety evaluation. These original tests are now being replaced gradually either by in vitro assays or by further refinements of in vivo methods such as the local lymph node assay. Human data have also been available to inform classification decisions for some substances and have been used by risk managers to introduce measures for exposure reduction. However, humans encounter hazards in the context of exposure rather than in the form of intrinsic hazards per se, and so in this article, we have examined critically the extent to which human data have been used to refine classification decisions and safety evaluations. We have also evaluated information on the burden of human allergic skin disease and used this to address the question of whether, and to what extent, the identification and evaluation of skin sensitization hazards has led to an improvement of public and/or occupational health.

Computational toxicology, friend or foe?

Computational approaches offer the attraction of being both fast and cheap to run being able to process thousands of chemical structures in a few minutes. As with all new technology, there is a tendency for these approaches to be hyped up and claims of reliability and performance may be exaggerated. So just how good are these computational methods?

Hexyl cinnamal: consideration of skin-sensitizing properties and suitability as a positive control

BACKGROUND

Hexyl cinnamal (HCA) is a widely used fragrance chemical, the low skin-sensitizing potency of which has made it a common choice for the use as a positive control for predictive toxicology assays. However, HCA is commonly negative in current candidate in vitro alternatives test methods.

OBJECTIVE

To review the evidence that HCA is a classifiable skin sensitizer against the standards set by the Globally Harmonized Scheme (GHS), and determine whether it represents an appropriate choice for a positive control substance for predictive testing.

METHODS

Using the GHS criteria, mechanistic data, and in vitro, in vivo and human evidence relating to HCA and skin sensitization have been reviewed.

RESULTS

The chemistry of HCA is consistent with potential for skin sensitization and predictive in vivo test data support this conclusion. However, the human data are relatively sparse, consistent with HCA possessing a low capacity to induce skin sensitization under conditions of consumer exposures.

CONCLUSIONS

Using GHS criteria (and applying a precautionary approach) HCA would classify as a weaker skin sensitizer than predicted by the local lymph node assay (LLNA). However, given the human experience, it is necessary to consider whether HCA is the most appropriate choice for use as a positive regulatory control.