Immunostaining of the normal mouse BM. Mouse BM whole-mount specimens were fluorescently double labeled with various combinations of lineage-specific antibodies for T and B cells, myeloid cells, megakaryocytes/platelets, and erythrocytes. In addition extracellular matrix was also visualized by perlecan staining. Each inset shows a higher magnification of a 100-μm² area of the corresponding confocal image, these depict a heterogeneous mixture of the main lineage cells: (A) CD3e⁺ T cells (green) appear scattered and much less numerous than CD45R⁺ B cells (red). (B) In contrast, CD11b⁺myeloid cells (red) are more abundant than B cells (green). (C) Megakaryocytes (large cells) and small platelets, both CD41⁺ (green), appear scattered evenly in the intertrabecullar space. (D) TER119⁺erythroid cells (green) are numerous and tend to form clusters. (E) CD45R⁺ B cells (red) are abundant and appear in close proximity to the extracellular matrix network (perlecan, white). (F) Hematopoietic stem and progenitor cells identified as double-labeled Sca1⁺ and cKit⁺ are scarce. A complex network of extracellular matrix surrounds and supports the cellular compartments (white in panels D-E). Scale bars are in micrometers. All results are representative of at least 3 independent experiments. Related images appear in supplemental Videos 4 and 5.