HPSE is expressed by BM environment cells and by a minor subpopulation of myeloma cells. (A) XG-2 and XG-7 cells were stained with control rabbit polyclonal antibodies (Abs) (i) or with a polyclonal anti-HPSE Ab at 4.5 μg/mL (ii-iii). Note the dotlike staining signal. (B) BM biopsies from patients with MM were stained with the polyclonal anti-HPSE Ab (4.5 μg/mL). (iv-vi) Environment cells in the BM of 1 patient representative of 20. PMN indicates polymorphonuclear cell; Meg, megakaryocyte. (vii-x) Heterogeneous HPSE expression among MMCs in the bone marrow of 4 representative patients (vii, patient 1; viii, patient 4; ix, patient 11; x, patient 20; see Table 2). The brown reaction product indicates the location of polyclonal Ab against HPSE. Original magnification, × 1000 (× 200 in vi).