Allergic contact dermatitis is a frequent and increasing health problem. Fo
r ethical reasons, the current animal tests used to screen for contact sens
itizers should be replaced by in vitro alternatives. Contact sensitizers ha
ve been shown to accelerate Langerhans cell (LC) migration from human organ
otypic skin explant cultures (hOSECs) more rapidly than non-sensitizers and
it has been proposed that the hOSEC model could be used to screen for sens
itizers. However, chemically induced decreases in epidermal LC numbers need
to be accurately quantified if the alterations in epidermal LC numbers are
to form the basis of an alternative system for screening contact sensitize
rs in vitro. As manual counting of LCs is labour intensive and subject to i
ntra- and inter-personal variation we developed an image analysis routine,
using the Leica QWin image analysis software, to quantify LCs in situ using
immunohistochemically stained skin sections. LCs can be identified using a
ntibodies against the membrane molecule CD1a or the Lag antibody, which rec
ognises cytoplasmic Birbeck granules. Quantification of epidermal LC number
using the image analysis software had a much lower inter-person variation
than when the same specimens were counted manually, using both the anti-lag
and CD1a antibodies. The software-aided quantification of epidermal LCs pr
ovides an accurate method for measuring chemically-induced changes in LC nu
mbers. (C) 2001 Elsevier Science B.V. All rights reserved.