Circulating MMM CD41⁺ megakaryocytic cells expressed IL-8 protein. Smears of blood mononuclear cells from patients with MMM were subjected to double labeling with anti-CD41 and anti–IL-8. The 3 panels show the same field of cells (magnification × 200). (A) Green fluorescent staining of anti-CD41–FITC. (B) Red-orange fluorescence staining of anti–IL-8–PE. (C) Double labeling of IL-8 and CD41 antigens. Slides were observed with a fluorescence microscope (Leica DMR, 200 × aperture .30, 400 × aperture .50; Leica, Heidelberg, Germany).