Immunohistochemical profile of multicentric reticulohistiocytosis.

BACKGROUND: There is enough evidence to support the knowledge that multicentric reticulohistiocytosis (MR) is a histiocytic proliferative disorder; however, the type of histiocytes involved is not well established.

OBJECTIVE AND METHODS: To study the nature of cells present in MR lesions by studying the immunohistochemical profile of three new cases and reviewing 23 cases reported in the literature.

RESULTS: MR histiocytic cells are positive for vimentin, CD68, and CD45, negative for S-100 protein, CD34, and XIIIa factor, and weak reactors for thrombomodulin. Small activated histiocytes are MAC387 positive. Lymphocytes, mainly CD4+ cells, are found in MR infiltrates.

CONCLUSIONS: The MR immunophenotypic pattern does not suggest a type I or type II dendrocyte or a Langerhans cell origin. On the other hand, it points to a different cell derived from the monocyte-macrophage line. CD4+ cells may be responsible for activating the proliferation of histiocytic cells. Small histiocytic MAC387+ cells are likely to become the MR multinucleated giant cells.