Chronic exposure to a trichloroethylene metabolite in autoimmune-prone MRL+/+ mice promotes immune modulation and alopecia. Toxicol Sci 95

The industrial solvent trichloroethylene (TCE) is a widespread environmental contaminant known to impact the immune system. In the present study, female MRL+/+ mice were treated for 40 weeks with trichloroacetaldehyde hydrate (TCAH), a metabolite of TCE, in the drinking water. The results were compared with the data from an earlier study in which MRL+/+ mice were exposed to TCAH for 4 weeks. Following a 40-week exposure, the mice developed skin inflammation and dose-dependent alopecia. In addition, TCAH appeared to modulate the CD4+ T-cell subset by promoting the expression of an activated/effector (i.e., CD62Llo) phenotype with an increased capacity to secrete the proinflam-matory cytokine interferon-g. However, unlike what was observed after only 4 weeks of exposure, TCAH did not significantly attenuate activation-induced cell death (AICD) or the expression of the death receptor FasL in CD4+ T cells. Some metalloprotein-ases (MMPs) are thought to play a role in susceptibility to AICD by inducing FasL shedding. Thus, both the 4- and 40-week sera were tested for MMP-7 levels in an attempt to explain the disparate results of TCAH on AICD and FasL expression. Serum MMP-7 levels were significantly higher in mice exposed to TCAH for 4 weeks. In contrast, the serum MMP-7 levels were increased in all the mice by 40 weeks when compared with a nonautoimmune strain. Taken together, a chronic exposure to TCAH promotes alopecia and skin inflammation. The early effects of TCAH on MMP-7 levels may provide a mechanism by which TCAH promotes skin pathology. Key Words: TCAH; rodent; CD4þ T cell; alopecia