INSITU VISUALIZATION OF HEMATOPOIETIC-CELL SUBSETS AND STROMAL ELEMENTS IN RAT AND MOUSE BONE-MARROW BY IMMUNOSTAINING OF FROZEN-SECTIONS

We have developed a method to section frozen long bones of rat and mouse and stained bone marrow (BM) by (double) immunofluorescence and immunoperoxidase. Here we report this method and reveal the location of early hemopoietic progenitors (Thy-1) and myeloid cells (Mac-1) in mouse BM, and early hemopoietic progenitors and lymphoid cells (Thy-1), erythroid cells (HIS49), and macrophages (ED2) in rat BM. In mouse BM our new findings include (a) the scattered localization of early hemopoietic progenitors (Thy-1low) all over the marrow, and (b) the presence of Thy-1+ stromal cells, mainly subendosteally. In rat BM an important finding is that of (a) a subendosteal region of 12-14 hemopoietic cell layers characterized by an abundance of Thy-1 and the virtual absence of erythroid cells, and (b) the scattering of Thy-1very bright cells which are candidates for the earliest hemopoietic progenitors in this species. The results illustrate that the technique is an excellent tool for studying the topology of BM as an organ of hemopoiesis.