Histology and somatic mutations of histiocytoses of group L, C, R, M, and H. (A) L group: Histology of LCH (skin [i-ii] and bone [iii]) and of ECD (perirenal [iv-v]). Pie chart of relative frequencies of activating kinase mutations in LCH (vi) and ECD (vii). (B) C group: Histology of JXG (i-ii). (C) R group: Histology of RDD (meningeal with high IgG4+ plasma cell infiltration [i-ii]). (D) M group: Histology of MH (i-ii). (E) H group: Histology of inherited HLH (liver [i-ii]). Staining with CD1a (Lii in red), IgG4 (Rii in brown), CD163 (Hii in brown), or hematoxylin and eosin (all others). NOS, not otherwise specified.