Constitutive JAK3 activation induces a T-cell lymphoproliferation with prominent cutaneous involvement. (A) H&E-stained skin tissue sections from JAK3-AV (top row and rightmost panel) or JAK3-WT (bottom row) animals showing a dense atypical dermal infiltrate comprised of pleomorphic lymphoid cells tagging along the dermal-epidermal junction in the former. (B) H&E-stained sections of skin lesions from secondary recipients display even more pronounced cutaneous disease, with significant involvement of the dermis and extension into subcutaneous adipose tissue. Sections of the epidermis highlight frequent collections of atypical intraepidermal lymphocytes resembling Pautrier microabcesses (indicated by). (C) Immunohistochemistry of skin sections from secondary recipients with anti-CD3 (left panel), anti-B220 (middle panel), or anti-CCR10 (right panel) antibodies. Insets show staining of intraepidermal lymphocyte collections highlighted in panel B.