Evidence of macrophage and lymphocyte, but not dendritic cell, infiltration in posterior uveal melanomas, whilst cultured uveal melanomas demonstrate pluripotency by expressing CD68 and CD163

Although variation in the level of macrophage infiltration has been reported in uveal melanoma, little is known about the expression of other leucocyte markers. An immuno- histochemistry study of the levels of expression of macrophage and other leucocyte markers, in a series of 10 primary choroidal melanoma biopsies, was undertaken. Biopsies were either fixed immediately in formalin and embedded in paraffin wax or established as short-term cultures. Using single- and double-labelling immunohistochemistry, cultured cells and paraffin sections were analysed for a range of melanoma (HMB45, Melan A, S100 and tyrosinase) and immune cell (CD68, CD163, CD45 and CD1a) markers. All samples expressed at least two known melanoma markers. Infiltrating macrophages were present in the majority of sections. When cultured specimens were studied by double-labelling immunofluorescence, uveal melanoma cells were seen to express macrophage markers or have cross-reactivity with related proteins. Expression of the leucocyte antigen CD45 was observed in three tumours but was not present in any cultured cells, whilst the expression of the dendritic cell marker CD1a was absent from all samples.