"Juvenile" xanthogranuloma - An immunophenotypic study with a reappraisal of histogenesis

The non-langerhans histiocytoses, a nosologic category to which juvenile xa nthogranuoma (JXG) belongs. represent a heterogenous collection of disorder s related to the monocyte/macrophage lineage. The dermal dendrocyte was pre viously proposed as the cell of origin for JXG on the basis of Factor XIIIa reactivity, a suggestion that does not fully explain the occasional xantho granulomatous proliferations localizing exclusively to extracutaneous sites . This study applies a panel of recently developed immunohistochemical mark ers to JXGs and relates the phenotype: of tills process to new concepts of monocyte/dendritic cell ontopeny. Twenty-seven JXG, ten dermatofibromas IDF ), and ten age-matched normal skin specimens were stained using standard im munohistochemistry methods, and all JXGs were fascin+ and CD68+, although 2 6 of 27 were reactive for HLA-DR, 25 of 27 for Factor,XIIIa, 25 of 27 for L CA: 21 of 27 for CD4, and 8 of 27 for polyclonal s100. Six of those eight p olyclonal S100+ cases wire also reactive for monoclonal S100. None of those cases was reactive for CD1a, CU3, CD21, CD31. of CD35. Eight of ten dermat ofibromas were FXIIIa+: all were negative for HLA-DR, LCA, CD4, and polyclo nal s100. In controls, fascin+ dendritic cells were present hut did not sta in for Factor XIIIa, S100, or CD I. Based on the morphologic and phenotypic overlap of the lesional cells in JXGs and plasmacytoid monocytes, it would appear that the plasmacytoid monocyte might de considered the putative nor mal counterpart of;he major cellular population of JXGs, a proposal that he lps explain the extra-cutaneous, visceral. and soft tissue location that ha ve been reported for occasional cases of JXG. We would also conclude that n either Factor XIIIa- nor S100+ results should preclude the diagnosis of JXG , and find that reactivity for CD4 and LCA may be used to distinguish JXG f rom DF when the latter is heavily lipidized or the former. is not.