CTCL cells are morphologically small CD3 ⁺ lymphocytes clustered around large granular class II ⁺ cells with dendritic appendages.

(A) Phase contrast microscopy (× 400) of cultured CTCL cells demonstrates that they have the morphology of small round lymphocytes. (B) The APCs were morphologically large granular cells with multiple dendritic extensions. (C) Immunofluorescent microscopy reveals that the CTCL cells are CD3⁺ (FITC, green) lymphocytes and the APCs express class II MHC molecules (phycoerythrin, red). (D) Phase contrast microscopy of the same field demonstrates the small round lymphocytes in direct contact with the membrane of large cells with multiple dendritic appendages. Original magnification × 400.