Identification of cellular origin of cytokines in LCH biopsies. Double immunohistochemical labeling was used to determine cytokine profiles of T cells and LCH cells in frozen sections of LCH biopsies. IL-1 (red) is not produced by CD3⁺ T cells (blue), as shown by the absence of intermediate (violet) staining (original magnification × 100). (B) In contrast to (A), all CD1a⁺ LCH cells (blue) also stain for IL-1 (red), resulting in violet double staining (original magnification × 100). (C) IL-5 (red) is not coexpressed with CD1a (blue) and is therefore not produced by LCH cells (original magnification × 100). (D) IL-4 (red)–producing cells stain violet with anti-CD3 (blue) and hence are T cells (original magnification × 100). (E) IFN-γ–producing cells stain in part double (note red, blue, and violet) with CD1a. Because the same was shown in double stainings with anti-CD3, this cytokine is produced by both T cells and LCH cells (original magnification × 200). (F) TNF-–producing cells coexpress CD3 and are therefore identified as T cells (original magnification × 100).