Pericellular matrix synthesized by MM B cells includes HA: MM B cells express intracellular HA. PEA in combination with indirect HA staining was used to verify the existence of HA molecules in the pericellular matrix detected by PEA on Figure 2. MM CD19⁺ B cells were cultured for 48 hours and then were incubated with B-HABP. HA binding to B-HABP was visualized using streptavidin Alexa 594. (A) CD19⁺ B cell without HA staining. (B) The cell and pericellular matrix around MM CD19⁺ B cells, which excluded fixed erythrocytes, were stained with streptavidin Alexa 594, indicating the presence of HA in the pericellular matrix. (C) Merged image of PEA and HA staining. (D) The cells were treated with HAase, which degraded the HA pericellular matrix. (E) HAase treatment also diminished cell surface HA staining. (F) Staining cells with B-HABP also detected intracellular HA in permeabilized MM CD19⁺ B cells. The staining pattern suggests that intracellular HA is distributed along the cell cytoskeleton and perinuclear compartment of MM B cells. Additionally, for one MM patient, weak nuclear staining of HA was observed in CD19⁺ B cells (not shown). Scale bar = 10 μm. Magnification 40×, numerical aperture 1.3. Images were processed using LSM 510 software.