What are Reed-Sternberg cells?

Reed-Sternberg (RS) cells are cells pathognomonic for Hodgkin's lymphoma. Although you do get variants, the classic RS cells are large, multinucleate cells, with the nuclei having prominent, esoinophilic nucleoli. The obvious, well-staining nucleoli can sometimes give the impression of an "owl's eye" (see below).

Although they are believed to be of B-cell origin (but with a 'crippled' imunoglobulin gene), they don't express the typical B-cell antigens. For what it's worth, they are usually CD15 and CD30 positive.

The RS cell is central to the diagnosis of the four 'classic' types of Hodgkin's lymphoma, but a fifth subtype has recently been described in which no RS cells are present.

Aaarrgh.