CTCL skin lesions contain a high-scatter population of T cells not seen in normal skin or lesional skin from 3 other T cell–mediated inflammatory skin disorders. (A) T cells were isolated from normal human skin (12 patients) or lesional skin from patients with atopic dermatitis (6 patients), contact dermatitis (1 patient), or psoriasis (6 patients) with the use of short-term explant cultures. All samples tested contained a single population of CD3⁺ T cells. (B) T cells were then isolated from CTCL skin lesions with the use of short-term explant cultures. Patients with all stages of CTCL exhibited 2 clear populations of T cells. The lower-scatter population had a forward scatter (reflecting size) and a side scatter (reflecting complexity) similar to that of T cells from normal skin, whereas the high-scatter population consisted of larger and more complex cells. Eight representative patients are shown, similar results were obtained in 30 additional patients. SSC-A indicates side-scatter area; FSC-H, forward-scatter height; PerCP, peridin chlorophyll protein; APC, allophycocyanin.