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EC number: 905-588-0
CAS number: -
Treatment with mixed xylene was associated
with a statistically significant increase in ear-draining lymph node
weight and cell count (indicative of a sensitisation response according
to criteria applied by the study authors) in 7 of the 9 laboratories
involved in the trial; and an increase in ear weight (indicative of
irritation according to criteria applied by the study authors) in 3 of 9
Although not discussed in any detail, one
laboratory also determined 3[H]TdR incorporation by lymph node cells in
vitro and obtained a "positive" result.
Overall, mixed xylene was classified as an
allergen in 8 of the 9 laboratories participating in the trial.
The sensitisation potential of mixed xylenes
was assessed in a modified local lymph node assay where increased
ear-draining lymph node weight and cell counts were used to quantify
lymph node cell proliferation by 9 laboratories participating in a
ring-trial. [3H]TdR incorporation in vitro by lymph node cells was also
assessed in a single laboratory (assay not conducted by other
laboratories). Acute skin inflammation (a potential confounder that can
lead to "false positive" results) was also determined based on changes
in ear tissue weight. Treatment with mixed xylenes was associated with a
statistically significant increase in ear-draining lymph node weight and
cell count in 7 of the 9 laboratories, and an increase in ear tissue
weight in 3 of 9 laboratories. An increased (but not quantified)
increase in 3[H]TdR incorporation by lymph node cells was also reported
by one laboratory. Based on these findings, mixed xylene was considered
an allergen by a majority of laboratories participating in the trial.
However the methodology used was evaluated by an ECVAM Workshop
(reported by Basketter et al., 2008) which concluded the assay methods
deviated from the Guideline in terms of the strain of mouse, the choice
of vehicle, the time of lymph node/lymph node cell collection, and the
magnitude of the SI used to differentiate positive and negative samples.
Overall, the ECVAM Workshop concluded that these differences represented
a major change in methodology that required further validation. The use
of [3H]TdR incorporation by lymph node cells in vitro (as opposed to
incorporation of [3H]TdR following i.v. injection in vivo, as required
by the Guideline) was not discussed by the ECVAM Workshop but is another
change relative to the Guideline. Basketter and Kimber (2010) also noted
that these findings for mixed xylenes can only be considered of limited
relevance given methodological deviations from the Guideline. It is
concluded that this publication does not provide convincing evidence
that mixed xylenes possesses a potential to induce or elicit skin
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