The activity of the mTOR signaling pathway is elevated in lymph nodes from patients with iMCD. (A) Schematic diagram outlining the mTOR signaling pathway, which is activated by engagement of cytokine or growth factor receptors with their respective ligands. The mTOR inhibitor sirolimus is used clinically to block mTOR signaling. (B-C) Lymph node sections from a control patient (B) or a patient with iMCD (C). Sections were stained with antibodies specific for the phosphorylated form of the ribosomal protein S6 (pS6; brown color), which becomes phosphorylated in response to mTOR signaling. Note the elevated levels of pS6 in the lymph node section from the iMCD patient relative to that from control, which signifies greater activation of mTOR signaling. The blue color represents staining of cell nuclei with hematoxylin. Original magnification ×20 for panels B-C. See Figure 1 in the article by Arenas et al that begins on page 1673.