Cell Contact and Direct Transfer Between Co‐Cultured Macrophages and Fibroblasts

Mouse peritoneal macrophages formed attachments with β‐glucuronidase deficient human fibroblasts within an hour after co‐cultures were initiated. Some of these attachments were transitory, while in others macrophages remained in firm contact with fibroblasts for many hours. Attachment of one macrophage did not prevent attachment of others, since many fibroblasts made firm contact with four or five other cells. Not all macrophages, however, attached themselves to fibroblasts. Macrophages injected with Lucifer yellow did not transfer the dye to fibroblasts with which they had made contact, nor was there any reverse transfer from injected fibroblasts to macrophages. Lucifer yellow was, however, transferred rapidly from injected fibroblasts to other adjacent fibroblasts with which they had formed gap junctions. Macrophages whose lysosomes had been pre‐loaded with FITC‐dextran did transfer this ligand to recipient fibroblasts, where it became localised in a perinuclear pattern with many bright punctate patches adjacent to donor macrophages. Transfer of FITC‐dextran was blocked when cells were separated by nucleopore membranes in an analogous manner to transfer of endogenous lysosomal β‐glucurondiase.