Cutaneous or mucosal DCs do not express CD52 in vivo.

(A) Normal skin. Intraepidermal DCs (LCs) are immunopositive for S-100 protein but negative for CD52. Apart from dermal inflammatory CD52⁺ T-cell aggregates that could be seen as an artifact of the punch biopsy in some sections (not shown), no CD52⁺dendritic profiles were seen in the dermis. Factor XIIIa staining confirmed the presence of dermal DCs (not shown). (B) Normal colon. CD52⁺ T lymphocytes surround a lymphoid follicle in a colonic biopsy. Mucosal DCs, which are immunopositive for S-100 protein, are negative for CD52. Germinal center B cells stained in this paraffin-embedded and -fixed tissue were also negative as expected. (C) GVHD affecting the skin. Intraepidermal and dermal DCs are immunopositive for S-100 protein, but negative for CD52. Inflammatory T lymphocytes that are destroying the dermal-epidermal interface as part of the graft-host reaction are CD52⁺, but there are no CD52⁺ dendritic profiles. (D) Drug hypersensitivity reaction in the skin. CD52⁺ lymphocytes are seen in the superficial dermis. S-100 protein–positive DCs are present in the epidermis and superficial dermis but are consistently negative for CD52. Staining was performed as described in “Immunohistochemistry.” Original magnification × 100.