Microscopic architecture of murine bone marrow: a histological and cytological perspective

Bone marrow, the primary lymphoid organ in mice, plays a pivotal role in haematopoiesis and immune function. In this study, we performed a comprehensive structural and cellular characterisation of murine bone marrow using histological sections and cytological smears from the tibia. Haematoxylin and eosin (HE) staining and field staining techniques were employed to elucidate the architecture and cellular composition of the marrow. The bone marrow was found to be highly cellular, with three distinct anatomical zones-endosteal, intermediate and central, though not sharply demarcated. The endosteal zone, adjacent to bony trabeculae, predominantly contained stromal and supporting cells, including fibroblasts and osteoblasts. Hematopoietic precursor cells were primarily located in the endosteal and intermediate zones, whereas mature blood cells were concentrated in the central zone. All major hematopoietic lineages were identified based on cell morphology, nuclear characteristics and staining patterns. The erythroid lineage displayed progressive maturation stages from proerythroblast to reticulocyte, characterised by changing cytoplasmic colour and nuclear morphology. The myeloid lineage included identifiable stages such as myeloblast, myelocyte, metamyelocyte and band forms, with mature granulocytes like neutrophils, eosinophils and basophils present. Monocytic lineage cells, including monocytes, were morphologically distinguishable by their kidney-shaped nuclei. Lymphoid cells were identified as small cells with dense nuclei and a peripheral crescent of cytoplasm. Megakaryocytes were prominent in histological sections, exhibiting multilobed nuclei and granular cytoplasm. Stromal elements such as adipocytes, fibroblasts, reticular and endothelial cells were observed in varying proportions.The myeloid to erythroid (M:E) ratio was calculated to be 2.62 0.11, indicating a predominance of myeloid elements in the marrow. This study provides a detailed anatomical and cytological map of murine bone marrow, serving as a reference for future haematological and immunological research.