Normal human keratinocyte assay to predict the human irritancy response

The potential to cause human skin irritation responses is part of the required information for the registration of new chemicals and for chemicals to conform to the new EU Chemical regulations under Registration, Evaluation, and Authorisation of Chemicals (REACH). The Fund for Replacement of Animals in Medical Experiments (FRAME) has developed an in vitro assay for potential human irritant responses via the skin, employing human passage 1-3 primary keratinocytes. The assay is based on two assessments: a direct assay of keratinocytes and an assay of the effect on macrophages of the mediators released by the keratinocytes. Keratinocyte activity is measured by the resazurin assay. Mediator activity is measured by assaying the release of nitric oxide (NO) following macrophage stimulation. It is also possible to measure release of interleukin-1alpha (IL-1alpha). Additional mediators are also released, but the precise range and composition of all these mediators are not clear at present. From time of exposure, this assay can be completed in 3-7 d; the exact timing is dependent on the rate and degree of recovery.

Shedding of mutant tumor necrosis factor receptor superfamily 1A associated with tumor necrosis factor receptor-associated periodic syndrome: Differences between cell types

OBJECTIVE

To investigate the effect of mutations in tumor necrosis factor receptor superfamily 1A (TNFRSF1A) on the ability of the receptors to be cleaved from the cell surface upon stimulation. The mutations we studied are associated with clinically distinct forms of TNF receptor-associated periodic syndrome (TRAPS). We also investigated different cell types within the same form of TRAPS.

METHODS

The shedding of TNFRSF1A in response to stimulation with phorbol myristate acetate was assessed in leukocytes and dermal fibroblasts from patients with C33Y TRAPS, and in HEK 293 cell lines stably transfected with constructs containing wild-type TNFRSF1A and/or TNFRSF1A mutants identified in TRAPS patients.

RESULTS

The shedding of TNFRSF1A differed between cell types within the same form of TRAPS. In particular, dermal fibroblasts, but not leukocytes, from C33Y TRAPS patients demonstrated reduced shedding of TNFRSF1A. Shedding of both wild-type and mutant TNFRSF1A from the transfected HEK 293 cells showed minor differences, but was in all cases induced to a substantial extent.

CONCLUSION

Differences in TNFRSF1A shedding are not purely a function of the TNFRSF1A structure, but are also influenced by other features of genetic makeup and/or cellular differentiation. It is unlikely that a defect in TNFRSF1A shedding per se can fully explain the clinical features that are common to TRAPS patients with different TNFRSF1A mutations.