Connective tissue elements in rat bone marrow: immunofluorescent visualization of the hematopoietic microenvironment

Immunofluorescent staining of frozen sections of rat bone marrow for collagen types I and III revealed the presence of a distinctive, collagen-producing cell type. Morphologically, these cells closely resembled reticular cells. They were large, with branching cytoplasm and were closely related to an extensive intercellular matrix of collagenous material that surrounded the hematopoietic cells of the marrow. Biochemical studies demonstrated synthesis of collagen types I and III, in a ratio of 4:1, by fresh rat bone marrow cells.