FcRH1 expression by peripheral blood mononuclear cells. Human blood mononuclear cells purified by Ficoll centrifugation were stained with biotinylated Fab fragments of 5A3 followed by streptavidin-APC and PE-conjugated antibodies to lineage specific markers: CD19⁺ B lineage cells, CD3⁺ T cells, CD14⁺ myeloid lineage cells, and CD56⁺ NK cells. Cells in the lymphocyte light-scatter gate were analyzed for CD19, CD3, and CD56, and cells in the myeloid gate are shown here for CD14 and FcRH1 staining. The same FcRH1 expression pattern was found for 10 donors of European, African, or Asian ancestry. Similar results were obtained with the 3B4 antibody.