Expression of T-lineage early developmental markers by cells establishing atopic dermatitis skin infiltrates

The association between the atopic dermatitis, eczema and T-cell immunodefi ciency disorders are well known, thus suggesting that bone marrow T-precurs ors could use the microenvironment of the skin as an extrathymic site for c ompensatory ontogenesis. In keeping with this hypothesis, we analyzed the a topic dermatitis skin lymphocytic infiltrate phenotypes to establish their ontogenetic stage of development. Cryostatic sections (4 mu m) obtained fro m acute lesional skin biopsies of six patients with extrinsic atopic dermat itis were processed with indirect immunoperoxidase, using a panel of first- step monoclonal antibodies (mAb) specific to CD104 (integrin beta 4 chain), CD90w (Thy 1 antigen), CD44 (phagocytic glycoprotein-1; Pgp-1), CD1a and t he DNA polymerase terminal deoxynucleotidyl transferase (TdT). Within the l ymphocytic dermal infiltrate different levels of immunoreactivity were obse rved with respect to CD104, CD90w and CD1a. A strong, spread staining was a lso detected for mAb specific to Pgp-1 and TdT Together the reported featur es indicate that the atopic dermatitis skin-homing lymphocytes express immu nophenotypes which are distinctive of the early T-ontogeny.