Expression of the colony-stimulating factor 1 receptor in B lymphocytes

The FMS proto-oncogene encodes for the colony-stimulating factor 1 receptor (CSF-1R), whose expression within the haematopoietic system has previously been thought to be restricted to cells of the mononuclear phagocyte lineage. We have studied the expression of the CSF-1R in peripheral blood mononuclear cells by indirect immunofluorescence and flow cytometry. FMS expression was detected on both monocytes and B lymphocytes from all samples analysed, including 14 haematologically normal individuals and 31 patients (23 in remission following cytotoxic therapy for lymphoma, six with B-cell chronic lymphocytic leukaemia and two with chronic myelomonocytic leukaemia). The level of FMS expression on B lymphocytes was lower than the level of expression detected on monocytes isolated from the same sample. FMS mRNA expression in B lymphocytes has been confirmed by a reverse transcription-polymerase chain reaction (RT-PCR)-based technique and Northern blot analysis. Thus, FMS may play a role in the normal function of B lymphocytes and, because of its potential oncogenic activity, may contribute to the pathogenesis of malignancies of this cell type.