SRGN and plasma cell myeloma: To determine if serglycin regulates the protein composition of exosomes, exosomes were isolated from equivalent volumes of conditioned medium from control (referred to as SRGN-exosomes) and SRGN-KD (referred to as SRGN-null exosomes) myeloma cells, layered on the top of a 40% iodixanol cushion, and centrifuged.