Immunohistochemical findings of the skin biopsy from case no. 9. The serial cryostat sections of skin biopsy specimens fixed in acetone were stained with control mouse IgG (A), OKT4 (B), anti-Tac (C), and 315 MoAb (D). Mononuclear cells infiltrating into upper dermis are clearly positive for CD4, Tac (IL-2 receptor α), and OX40.